1 // Render with Asciidoctor
3 = Babeltrace{nbsp}2 contributor's guide
4 Jérémie Galarneau, Philippe Proulx
10 :bt2: Babeltrace{nbsp}2
14 This is a partial contributor's guide for the
15 https://babeltrace.org[{bt2}] project. If you have any
16 questions that are not answered by this guide, please post them on
17 https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev[Babeltrace's
22 === Object reference counting and lifetime
24 This section covers the rationale behind the design of {bt2}'s
25 object lifetime management. This applies to the {bt2} library, as
26 well as to the CTF writer library (although the public reference
27 counting functions are not named the same way).
29 Starting from Babeltrace{nbsp}2.0, all publicly exposed objects inherit
30 a common base: `bt_object`. This base provides a number of facilities to
31 all objects, chief amongst which are lifetime management functions.
33 The lifetime of some public objects is managed by reference counting. In
34 this case, the API offers the `+bt_*_get_ref()+` and `+bt_*_put_ref()+`
35 functions which respectively increment and decrement an object's
38 As far as lifetime management in concerned, {bt2} makes a clear
39 distinction between regular objects, which have a single parent, and
40 root objects, which don't.
44 Let us consider a problematic case to illustrate the need for this
47 A user of the {bt2} library creates a trace class, which _has_ a
48 stream class (the class of a stream) and that stream class, in turn,
49 _has_ an event class (the class of an event).
51 Nothing prevents this user from releasing his reference on any one of
52 these objects in any order. However, all objects in the
53 __trace--stream class--event class__ hierarchy can be retrieved
56 For instance, the user could discard his reference on both the event
57 class and the stream class, only keeping a reference on the trace class.
58 From this trace class reference, stream classes can be enumerated,
59 providing the user with a new reference to the stream class he discarded
60 earlier. Event classes can also be enumerated from stream classes,
61 providing the user with references to the individual event classes.
63 Conversely, the user could also hold a reference to an event class and
64 retrieve its parent stream class. The trace class, in turn, can then be
65 retrieved from the stream class.
67 This example illustrates what could be interpreted as a circular
68 reference dependency existing between these objects. Of course, if the
69 objects in such a scenario were to hold references to each other (in
70 both directions), we would be in presence of a circular ownership
71 resulting in a leak of both objects as their reference counts would
74 Nonetheless, the API must offer the guarantee that holding a node to any
75 node of the graph keeps all other reachable nodes alive.
79 The scheme employed in {bt2} to break this cycle consists in the
80 "children" holding _reverse component references_ to their parents. That
81 is, in the context of the trace IR, that event classes hold a reference
82 to their parent stream class and stream classes hold a reference to
83 their parent trace class.
85 On the other hand, parents hold _claiming aggregation references_ to
86 their children. A claiming aggregation reference means that the object
87 being referenced should not be deleted as long as the reference still
88 exists. In this respect, it can be said that parents truly hold the
89 ownership of their children, since they control their lifetime.
90 Conversely, the reference counting mechanism is leveraged by children to
91 notify parents that no other child indirectly exposes the parent.
93 When a parented object's reference count reaches zero, it invokes
94 `+bt_*_put_ref()+` on its parent and does _not_ free itself. However,
95 from that point, the object depends on its parent to signal the moment
96 when it can be safely reclaimed.
98 The invocation of `+bt_*_put_ref()+` by the last children holding a
99 reference to its parent might trigger a cascade of `+bt_*_put_ref()+`
100 from child to parent. Eventually, a **root** object is reached. At that
101 point, if this orphaned object's reference count reaches zero, the
102 object invokes the destructor method defined by everyone of its children
103 as part of their base `struct bt_object`. The key point here is that the
104 cascade of destructor will necessarily originate from the root and
105 propagate in preorder to the children. These children will propagate the
106 destruction to their own children before reclaiming their own memory.
107 This ensures that a node's pointer to its parent is _always_ valid since
108 the parent has the responsibility of tearing-down their children before
109 cleaning themselves up.
111 Assuming a reference to an object is _acquired_ by calling
112 `+bt_*_get_ref()+` while its reference count is zero, the object
113 acquires, in turn, a reference on its parent using `+bt_*_get_ref()+`.
114 At that point, the child can be thought of as having converted its weak
115 reference to its parent into a regular reference. That is why this
116 reference is referred to as a _claiming_ aggregation reference.
120 This scheme imposes a number of strict rules defining the relation
123 * Objects may only have one parent.
124 * Objects, beside the root, are only retrievable from their direct
129 The initial situation is rather simple: **User{nbsp}A** is holding a
130 reference to a trace class, **TC1**. As per the rules previously
131 enounced, stream classes **SC1** and **SC2** don't hold a reference to
132 **TC1** since their own reference counts are zero. The same holds true
133 for **EC1**, **EC2** and **EC3** with respect to **SC1** and **SC2**.
135 image::doc/contributing-images/bt-ref01.png[]
137 In this second step, we can see that **User{nbsp}A** has acquired a
138 reference on **SC2** through the trace class, **TC1**.
140 The stream class's reference count transitions from zero to one,
141 triggering the acquisition of a strong reference on **TC1** from
144 Hence, at this point, the trace class's ownership is shared by
145 **User{nbsp}A** and **SC2**.
147 image::doc/contributing-images/bt-ref02.png[]
149 Next, **User{nbsp}A** acquires a reference on the **EC3** event class
150 through its parent stream class, **SC2**. Again, the transition of an
151 object's reference count from 0 to 1 triggers the acquisition of a
152 reference on its parent.
154 Note that SC2's reference count was incremented to 2. The trace class's
155 reference count remains unchanged.
157 image::doc/contributing-images/bt-ref03.png[]
159 **User{nbsp}A** decides to drop its reference on **SC2**. **SC2**'s
160 reference count returns back to 1, everything else remaining unchanged.
162 image::doc/contributing-images/bt-ref04.png[]
164 **User{nbsp}A** can then decide to drop its reference on the trace
165 class. This results in a reversal of the initial situation:
166 **User{nbsp}A** now owns an event, **EC3**, which is keeping everything
167 else alive and reachable.
169 image::doc/contributing-images/bt-ref05.png[]
171 If another object, **User{nbsp}B**, enters the picture and acquires a
172 reference on the **SC1** stream class, we see that **SC1**'s reference
173 count transitioned from 0 to 1, triggering the acquisition of a
174 reference on **TC1**.
176 image::doc/contributing-images/bt-ref06.png[]
178 **User{nbsp}B** hands off a reference to **EC1**, acquired through
179 **SC1**, to another object, **User{nbsp}C**. The acquisition of a
180 reference on **EC1**, which transitions from 0 to 1, triggers the
181 acquisition of a reference on its parent, **SC1**.
183 image::doc/contributing-images/bt-ref07.png[]
185 At some point, **User{nbsp}A** releases its reference on **EC3**. Since
186 **EC3**'s reference count transitions to zero, it releases its reference
187 on **SC2**. **SC2**'s reference count, in turn, reaches zero and it
188 releases its reference to **TC1**.
190 **TC1**'s reference count is now 1 and no further action is taken.
192 image::doc/contributing-images/bt-ref08.png[]
194 **User{nbsp}B** releases its reference on **SC1**. **User{nbsp}C**
195 becomes the sole owner of the whole hierarchy through his ownership of
198 image::doc/contributing-images/bt-ref09.png[]
200 Finally, **User{nbsp}C** releases his ownership of **EC1**, triggering
201 the release of the whole hierarchy. Let's walk through the reclamation
204 Mirroring what happened when **User{nbsp}A** released its last reference
205 on **EC3**, the release of **EC1** by **User{nbsp}C** causes its
206 reference count to fall to zero.
208 This transition to zero causes **EC1** to release its reference on
209 **SC1**. **SC1**'s reference count reaching zero causes it to release
210 its reference on **TC1**.
212 image::doc/contributing-images/bt-ref10.png[]
214 Since the reference count of **TC1**, a root object, has reached zero,
215 it invokes the destructor method on its children. This method is
216 recursive and causes the stream classes to call the destructor method on
219 The event classes are reached and, having no children of their own, are
222 image::doc/contributing-images/bt-ref11.png[]
224 The stream classes having destroyed their children, are then reclaimed
227 image::doc/contributing-images/bt-ref12.png[]
229 Finally, the stream classes having been reclaimed, **TC1** is reclaimed.
231 image::doc/contributing-images/bt-ref13.png[]
236 Logging is a great instrument for a developer to be able to collect
237 information about a running software.
239 {bt2} is a complex software with many layers. When a {bt2}
240 graph fails to run, what caused the failure? It could be caused by any
241 component, any message iterator, and any deeply nested validation of a
242 CTF IR object (within the `ctf` plugin), for example. With the
243 appropriate logging statements manually placed in the source code, we
244 can find the cause of a bug faster.
246 While <<choose-a-log-level,care must be taken>> when placing _DEBUG_ to
247 _FATAL_ logging statements, you should liberally instrument your
248 {bt2} module with _TRACE_ logging statements to help future you
249 and other developers understand what's happening at run time.
253 The {bt2} logging API is internal: it is not exposed to the users
254 of the library; only to their developers. The only thing that a library
255 user can control is the current log level of the library itself with
256 `bt_logging_set_global_level()` and the initial library's log level with
257 the `LIBBABELTRACE2_INIT_LOG_LEVEL` environment variable.
259 This API is based on https://github.com/wonder-mice/zf_log[zf_log], a
260 lightweight, yet featureful, MIT-licensed core logging library for C and
261 {cpp}. The zf_log source files were modified to have the `BT_` and
262 `bt_` prefixes, and other small changes, like color support and using
263 the project's `BT_DEBUG_MODE` definition instead of the standard
266 The logging functions are implemented in the logging convenience
267 library (`src/logging` directory).
272 The logging API headers are:
274 `<babeltrace2/logging.h>`::
275 Public header which a library user can use to set and get
276 libbabeltrace2's current log level.
279 Internal, generic logging API which you can use in any {bt2}
280 module. This is the translation of `zf_log.h`.
282 This header offers the <<gen-logging-statements,generic logging
286 Specific internal header to use within the library.
288 This header defines `BT_LOG_OUTPUT_LEVEL` to a custom, library-wide
289 hidden symbol which is the library's current log level before including
292 This header offers the <<lib-logging-statements,library-specific logging
295 `"logging/comp-logging.h"`::
296 Specific internal header to use within a component class.
298 This header offers the <<comp-logging-statements,component-specific
299 logging statement macros>>.
304 The internal logging API offers the following log levels, in ascending
307 [options="header,autowidth",cols="4"]
310 |Log level short name
311 |Internal API enumerator
312 |Public API enumerator
317 |`BT_LOGGING_LEVEL_TRACE`
322 |`BT_LOGGING_LEVEL_DEBUG`
327 |`BT_LOGGING_LEVEL_INFO`
332 |`BT_LOGGING_LEVEL_WARNING`
337 |`BT_LOGGING_LEVEL_ERROR`
342 |`BT_LOGGING_LEVEL_FATAL`
347 |`BT_LOGGING_LEVEL_NONE`
350 The short name is accepted by the log level environment variables and by
351 the CLI's `--log-level` options.
353 See <<choose-a-log-level,how to decide which one to use>> below.
355 There are two important log level expressions:
357 [[build-time-log-level]]Build-time, minimal log level::
358 The minimal log level, or build-time log level, is set at build time
359 and determines the minimal log level of the logging statements which
360 can be executed. This applies to all the modules (CLI, library,
361 plugins, bindings, etc.).
363 All the logging statements with a level below this level are **not built
364 at all**. All the logging statements with a level equal to or greater
365 than this level _can_ be executed, depending on the
366 <<run-time-log-level,run-time log level>>.
368 You can set this level at configuration time with the
369 `BABELTRACE_MINIMAL_LOG_LEVEL` environment variable, for example:
373 $ BABELTRACE_MINIMAL_LOG_LEVEL=INFO ./configure
377 The default build-time log level is `DEBUG`. For optimal performance,
378 set it to `INFO`, which effectively disables all fast path logging in
379 all the {bt2} modules. You can't set it to `WARNING`, `ERROR`,
380 `FATAL`, or `NONE` because the impact on performance is minuscule
381 starting from the _INFO_ log level anyway and we want any {bt2}
382 build to always be able to print _INFO_-level logs.
384 The library's public API provides `bt_logging_get_minimal_level()` to
385 get the configured minimal log level.
387 [[run-time-log-level]]Run-time, dynamic log level::
388 The dynamic log level is set at run time and determines the current,
389 _active_ log level. All the logging statements with a level below
390 this level are not executed, **but they still evaluate the
391 condition**. All the logging statements with a level equal to or
392 greater than this level are executed, provided that their level is
393 also <<build-time-log-level,enabled at build time>>.
395 `zf_log` has a concept of a global run-time log level which uses the
396 `_bt_log_global_output_lvl` symbol. In practice, we never use this
397 symbol, and always make sure that `BT_LOG_OUTPUT_LEVEL` is defined to a
398 module-wise expression before including `"logging/log.h"`.
400 In the library, `"lib/logging.h"` defines its own
401 `BT_LOG_OUTPUT_LEVEL` to the library's log level symbol before it
402 includes `"logging/log.h"` itself.
404 In libbabeltrace2, the user can set the current run-time log level with
405 the `bt_logging_set_global_level()` function, for example:
410 bt_logging_set_global_level(BT_LOGGING_LEVEL_INFO);
414 The library's initial run-time log level is defined by the
415 `LIBBABELTRACE2_INIT_LOG_LEVEL` environment variable, or set to _NONE_
416 if this environment variable is undefined.
418 Other modules have their own way of setting their run-time log level.
420 For example, the CLI uses the `BABELTRACE_CLI_LOG_LEVEL` environment
421 variable, as well as its global `--log-level` option:
424 $ babeltrace2 --log-level=I ...
427 The components use their own log level (as returned by
428 `bt_component_get_logging_level()`). With the CLI, you can set a
429 specific component's log level with its own, position-dependent
430 `--log-level` option:
433 $ babeltrace2 /path/to/trace -c sink.ctf.fs --log-level=D
436 Code which is common to the whole project, for example `src/common`
437 and `src/compat`, use function parameters to get its run-time log
443 char *bt_common_get_home_plugin_path(int log_level);
446 Typically, when a logging-enabled module calls such a function, it
447 passes its own log level expression directly (`BT_LOG_OUTPUT_LEVEL`):
451 path = bt_common_get_home_plugin_path(BT_LOG_OUTPUT_LEVEL);
454 Otherwise, just pass `BT_LOG_NONE`:
457 path = bt_common_get_home_plugin_path(BT_LOG_NONE);
460 [[gen-logging-statements]]
461 ==== Generic logging statement macros
463 The {bt2} logging statement macros work just like `printf()`
464 (except the `+BT_LOG*_STR()+` ones) and contain their <<log-levels,log
465 level>> (short name) in their name.
467 Each of the following macros evaluate the
468 <<build-time-log-level,build-time log level>> definition and
469 <<run-time-log-level,run-time log level>> expression (as defined by
470 `BT_LOG_OUTPUT_LEVEL`) to log conditionally.
472 See <<logging-instrument-c-file-gen>> and
473 <<logging-instrument-h-file-gen>> to learn how to be able to use the
476 `+BT_LOGT("format string", ...)+`::
477 Generic trace logging statement.
479 `+BT_LOGD("format string", ...)+`::
480 Generic debug logging statement.
482 `+BT_LOGI("format string", ...)+`::
483 Generic info logging statement.
485 `+BT_LOGW("format string", ...)+`::
486 Generic warning logging statement.
488 `+BT_LOGE("format string", ...)+`::
489 Generic error logging statement.
491 `+BT_LOGF("format string", ...)+`::
492 Generic fatal logging statement.
494 `+BT_LOGT_STR("preformatted string")+`::
495 Generic preformatted string trace logging statement.
497 `+BT_LOGD_STR("preformatted string")+`::
498 Generic preformatted string debug logging statement.
500 `+BT_LOGI_STR("preformatted string")+`::
501 Generic preformatted string info logging statement.
503 `+BT_LOGW_STR("preformatted string")+`::
504 Generic preformatted string warning logging statement.
506 `+BT_LOGE_STR("preformatted string")+`::
507 Generic preformatted string error logging statement.
509 `+BT_LOGF_STR("preformatted string")+`::
510 Generic preformatted string fatal logging statement.
512 `+BT_LOGT_MEM(data_ptr, data_size, "format string", ...)+`::
513 Generic memory trace logging statement.
515 `+BT_LOGD_MEM(data_ptr, data_size, "format string", ...)+`::
516 Generic memory debug logging statement.
518 `+BT_LOGI_MEM(data_ptr, data_size, "format string", ...)+`::
519 Generic memory info logging statement.
521 `+BT_LOGW_MEM(data_ptr, data_size, "format string", ...)+`::
522 Generic memory warning logging statement.
524 `+BT_LOGE_MEM(data_ptr, data_size, "format string", ...)+`::
525 Generic memory error logging statement.
527 `+BT_LOGF_MEM(data_ptr, data_size, "format string", ...)+`::
528 Generic memory fatal logging statement.
530 `+BT_LOGT_ERRNO("initial message", "format string", ...)+`::
531 Generic `errno` string trace logging statement.
533 `+BT_LOGD_ERRNO("initial message", "format string", ...)+`::
534 Generic `errno` string debug logging statement.
536 `+BT_LOGI_ERRNO("initial message", "format string", ...)+`::
537 Generic `errno` string info logging statement.
539 `+BT_LOGW_ERRNO("initial message", "format string", ...)+`::
540 Generic `errno` string warning logging statement.
542 `+BT_LOGE_ERRNO("initial message", "format string", ...)+`::
543 Generic `errno` string error logging statement.
545 `+BT_LOGF_ERRNO("initial message", "format string", ...)+`::
546 Generic `errno` string fatal logging statement.
548 [[lib-logging-statements]]
549 ==== Library-specific logging statement macros
551 The {bt2} library contains an internal logging API based on the
552 generic logging framework. You can use it to log known {bt2}
553 objects without having to manually log each member.
555 See <<logging-instrument-c-file-lib>>
556 and <<logging-instrument-h-file-lib>> to
557 learn how to be able to use the following macros.
559 The library logging statement macros are named `+BT_LIB_LOG*()+` instead
562 `+BT_LIB_LOGT("format string", ...)+`::
563 Library trace logging statement.
565 `+BT_LIB_LOGD("format string", ...)+`::
566 Library debug logging statement.
568 `+BT_LIB_LOGI("format string", ...)+`::
569 Library info logging statement.
571 `+BT_LIB_LOGW("format string", ...)+`::
572 Library warning logging statement.
574 `+BT_LIB_LOGE("format string", ...)+`::
575 Library error logging statement.
577 `+BT_LIB_LOGF("format string", ...)+`::
578 Library fatal logging statement.
580 `+BT_LIB_LOGW_APPEND_CAUSE("format string", ...)+`::
581 Library warning logging statement, and unconditional error cause
584 `+BT_LIB_LOGE_APPEND_CAUSE("format string", ...)+`::
585 Library error logging statement, and unconditional error cause
588 `+BT_LIB_LOGF_APPEND_CAUSE("format string", ...)+`::
589 Library fatal logging statement, and unconditional error cause
592 The macros above accept the typical `printf()` conversion specifiers
593 with the following limitations:
595 * The `+*+` width specifier is not accepted.
596 * The `+*+` precision specifier is not accepted.
597 * The `j` and `t` length modifiers are not accepted.
598 * The `n` format specifier is not accepted.
599 * The format specifiers defined in `<inttypes.h>` are not accepted,
600 except for `PRId64`, `PRIu64`, `PRIx64`, `PRIX64`, `PRIo64`, and
603 The {bt2} library custom conversion specifier is accepted. Its
604 syntax is either `%!u` to format a UUID (`bt_uuid` type), or:
606 . Introductory `%!` sequence.
608 . **Optional**: `[` followed by a custom prefix for the printed fields
609 of this specifier, followed by `]`. The standard form is to end this
610 prefix with `-` so that, for example, with the prefix `tc-`, the
611 complete field name becomes `tc-addr`.
613 . **Optional**: `pass:[+]` to print extended object members. This
614 depends on the provided format specifier.
616 . Format specifier (see below).
618 The available format specifiers are:
620 [options="header,autowidth",cols="3"]
627 |Trace IR field class
628 |`+const struct bt_field_class *+`
632 |`+const struct bt_field *+`
636 |`+const struct bt_field_path *+`
639 |Trace IR event class
640 |`+const struct bt_event_class *+`
644 |`+const struct bt_event *+`
647 |Trace IR stream class.
648 |`+const struct bt_stream_class *+`
652 |`+const struct bt_stream *+`
656 |`+const struct bt_packet *+`
659 |Trace IR trace class
660 |`+const struct bt_trace_class *+`
664 |`+const struct bt_trace *+`
667 |Trace IR clock class
668 |`+const struct bt_clock_class *+`
671 |Trace IR clock snapshot
672 |`+const struct bt_clock_snapshot *+`
676 |`+const struct bt_value *+`
680 |`const struct bt_integer_range_set *`
684 |`+const struct bt_message *+`
687 |Message iterator class
688 |`struct bt_message_iterator_class *`
692 |`struct bt_message_iterator *`
696 |`struct bt_component_class *`
700 |`+const struct bt_component *+`
704 |`+const struct bt_port *+`
708 |`+const struct bt_connection *+`
712 |`+const struct bt_graph *+`
716 |`+struct bt_interrupter *+`
720 |`+const struct bt_plugin *+`
724 |`+const struct bt_error_cause *+`
728 |`+const struct bt_object_pool *+`
732 |`+const struct bt_object *+`
735 Conversion specifier examples:
742 The ``, `` string (comma and space) is printed between individual
743 fields, but **not after the last one**. Therefore, you must put this
744 separator in the format string between two conversion specifiers, for
749 BT_LIB_LOGW("Message: count=%u, %!E, %!+K", count, event_class, clock_class);
752 Example with a custom prefix:
756 BT_LIB_LOGI("Some message: %![ec-a-]e, %![ec-b-]+e", ec_a, ec_b);
759 It is safe to pass `NULL` as any {bt2} object parameter: the macros
760 only print its null address.
762 WARNING: Build-time `printf()` format checks are disabled for the
763 `+BT_LIB_LOG*()+` macros because there are custom conversion specifiers,
764 so make sure to test your logging statements.
766 [[comp-logging-statements]]
767 ==== Component-specific logging statement macros
769 There are available logging macros for components. They prepend a prefix
770 including the component's name to the logging message.
772 See <<logging-instrument-c-file-compcls>> and
773 <<logging-instrument-h-file-compcls>> to learn how to be able to use the
776 The component logging statement macros are named `+BT_COMP_LOG*()+`
777 instead of `+BT_LOG*()+`:
779 `+BT_COMP_LOGT("format string", ...)+`::
780 Component trace logging statement.
782 `+BT_COMP_LOGD("format string", ...)+`::
783 Component debug logging statement.
785 `+BT_COMP_LOGI("format string", ...)+`::
786 Component info logging statement.
788 `+BT_COMP_LOGW("format string", ...)+`::
789 Component warning logging statement.
791 `+BT_COMP_LOGE("format string", ...)+`::
792 Component error logging statement.
794 `+BT_COMP_LOGF("format string", ...)+`::
795 Component fatal logging statement.
797 `+BT_COMP_LOGT_STR("preformatted string")+`::
798 Component preformatted string trace logging statement.
800 `+BT_COMP_LOGD_STR("preformatted string")+`::
801 Component preformatted string debug logging statement.
803 `+BT_COMP_LOGI_STR("preformatted string")+`::
804 Component preformatted string info logging statement.
806 `+BT_COMP_LOGW_STR("preformatted string")+`::
807 Component preformatted string warning logging statement.
809 `+BT_COMP_LOGE_STR("preformatted string")+`::
810 Component preformatted string error logging statement.
812 `+BT_COMP_LOGF_STR("preformatted string")+`::
813 Component preformatted string fatal logging statement.
815 `+BT_COMP_LOGT_ERRNO("initial message", "format string", ...)+`::
816 Component `errno` string trace logging statement.
818 `+BT_COMP_LOGD_ERRNO("initial message", "format string", ...)+`::
819 Component `errno` string debug logging statement.
821 `+BT_COMP_LOGI_ERRNO("initial message", "format string", ...)+`::
822 Component `errno` string info logging statement.
824 `+BT_COMP_LOGW_ERRNO("initial message", "format string", ...)+`::
825 Component `errno` string warning logging statement.
827 `+BT_COMP_LOGE_ERRNO("initial message", "format string", ...)+`::
828 Component `errno` string error logging statement.
830 `+BT_COMP_LOGF_ERRNO("initial message", "format string", ...)+`::
831 Component `errno` string fatal logging statement.
833 `+BT_COMP_LOGT_MEM(data_ptr, data_size, "format string", ...)+`::
834 Component memory trace logging statement.
836 `+BT_COMP_LOGD_MEM(data_ptr, data_size, "format string", ...)+`::
837 Component memory debug logging statement.
839 `+BT_COMP_LOGI_MEM(data_ptr, data_size, "format string", ...)+`::
840 Component memory info logging statement.
842 `+BT_COMP_LOGW_MEM(data_ptr, data_size, "format string", ...)+`::
843 Component memory warning logging statement.
845 `+BT_COMP_LOGE_MEM(data_ptr, data_size, "format string", ...)+`::
846 Component memory error logging statement.
848 `+BT_COMP_LOGF_MEM(data_ptr, data_size, "format string", ...)+`::
849 Component memory fatal logging statement.
851 ==== Conditional logging
853 `+BT_LOG_IF(cond, statement)+`::
854 Execute `statement` only if `cond` is true.
861 BT_LOG_IF(i < count / 2, BT_LOGD("Log this: i=%d", i));
865 To check the <<build-time-log-level,build-time log level>>:
869 #if BT_LOG_ENABLED_DEBUG
874 This tests if the _DEBUG_ level was enabled at build time. This means
875 that the current, <<run-time-log-level,run-time log level>> _could_ be
876 _DEBUG_, but it could also be higher. The rule of thumb is to use only
877 logging statements at the same level in a `BT_LOG_ENABLED_*` conditional
880 The available definitions for build-time conditions are:
882 * `BT_LOG_ENABLED_TRACE`
883 * `BT_LOG_ENABLED_DEBUG`
884 * `BT_LOG_ENABLED_INFO`
885 * `BT_LOG_ENABLED_WARNING`
886 * `BT_LOG_ENABLED_ERROR`
887 * `BT_LOG_ENABLED_FATAL`
889 To check the current, <<run-time-log-level,run-time log level>>:
893 if (BT_LOG_ON_DEBUG) {
898 This tests if the _DEBUG_ log level is dynamically turned on
899 (implies that it's also enabled at build time). This check could have a
900 noticeable impact on performance.
902 The available definitions for run-time conditions are:
907 * `BT_LOG_ON_WARNING`
911 Those macros check the module-specific log level symbol (defined by
912 `BT_LOG_OUTPUT_LEVEL`).
914 Never, ever write code which would be executed only to compute the
915 fields of a logging statement outside a conditional logging scope,
920 int number = get_number_of_event_classes_with_property_x(...);
921 BT_LOGD("Bla bla: number=%d", number);
928 if (BT_LOG_ON_DEBUG) {
929 int number = get_number_of_event_classes_with_property_x(...);
930 BT_LOGD("Bla bla: number=%d", number);
938 BT_LOGD("Bla bla: number=%d", get_number_of_event_classes_with_property_x(...));
943 [[logging-instrument-c-file-gen]]
944 ==== Instrument a {c-cpp} source file (generic)
946 To instrument a {c-cpp} source file (`.c`/`.cpp`):
948 . At the top of the file, before the first `#include` line (if any),
949 define your file's <<choose-a-logging-tag,logging tag>> name:
954 #define BT_LOG_TAG "SUBSYS/MY-MODULE/MY-FILE"
958 . Below the line above, define the source file's log level expression,
959 `BT_LOG_OUTPUT_LEVEL`. This expression is evaluated for each
960 <<gen-logging-statements,logging statement>> to know the current
961 <<run-time-log-level,run-time log level>>.
967 /* Global log level variable */
968 #define BT_LOG_OUTPUT_LEVEL module_global_log_level
973 /* Local log level variable; must exist where you use BT_LOG*() */
974 #define BT_LOG_OUTPUT_LEVEL log_level
979 /* Object's log level; `obj` must exist where you use BT_LOG*() */
980 #define BT_LOG_OUTPUT_LEVEL (obj->log_level)
983 . Include `"logging/log.h"`:
987 #include "logging/log.h"
990 . In the file, instrument your code with the
991 <<gen-logging-statements,generic logging statement macros>>.
993 [[logging-instrument-h-file-gen]]
994 ==== Instrument a {c-cpp} header file (generic)
996 To instrument a {c-cpp} header file (`.h`/`.hpp`), if you have
997 `static inline` functions in it:
999 . Do not include `"logging/log.h"`!
1003 .. In the file, instrument your code with the
1004 <<gen-logging-statements,generic logging statement macros>>, making
1005 each of them conditional to the existence of the macro you're using:
1010 int some_function(int x)
1028 The {c-cpp} source files which include this header file determine if
1029 logging is enabled or not for them, and if so, what is their
1030 <<choose-a-logging-tag,logging tag>> and <<run-time-log-level,run-time
1031 log level>> expression.
1033 .. Require that logging be enabled:
1037 /* Protection: this file uses BT_LOG*() macros directly */
1038 #ifndef BT_LOG_SUPPORTED
1039 # error Please include "logging/log.h" before including this file.
1043 Then, in the file, instrument your code with the
1044 <<gen-logging-statements,generic logging statement macros>>.
1046 [[logging-instrument-c-file-lib]]
1047 ==== Instrument a library {c-cpp} source file
1049 To instrument a library {c-cpp} source file (`.c`/`.cpp`):
1051 . At the top of the file, before the first `#include` line (if any),
1052 define your file's <<choose-a-logging-tag,logging tag>> name (this
1053 tag must start with `LIB/`):
1058 #define BT_LOG_TAG "LIB/THE-FILE"
1062 . Include `"lib/logging.h"`:
1066 #include "lib/logging.h"
1069 . In the file, instrument your code with the
1070 <<lib-logging-statements,library logging statement macros>> or with
1071 the <<gen-logging-statements,generic logging statement macros>>.
1073 [[logging-instrument-h-file-lib]]
1074 ==== Instrument a library {c-cpp} header file
1076 To instrument a library {c-cpp} header file (`.h`/`.hpp`), if you have
1077 `static inline` functions in it:
1079 . Do not include `"lib/logging.h"`!
1081 . Require that library logging be enabled:
1085 /* Protection: this file uses BT_LIB_LOG*() macros directly */
1086 #ifndef BT_LIB_LOG_SUPPORTED
1087 # error Please include "lib/logging.h" before including this file.
1091 . In the file, instrument your code with the
1092 <<lib-logging-statements,library logging statement macros>> or with
1093 the <<gen-logging-statements,generic logging statement macros>>.
1095 [[logging-instrument-c-file-compcls]]
1096 ==== Instrument a component class {c-cpp} source file
1098 To instrument a component class {c-cpp} source file (`.c`/`.cpp`):
1100 . At the top of the file, before the first `#include` line (if any),
1101 define your file's <<choose-a-logging-tag,logging tag>> name (this tag
1102 must start with `PLUGIN/` followed by the component class identifier):
1107 #define BT_LOG_TAG "PLUGIN/SRC.MY-PLUGIN.MY-SRC"
1111 . Below the line above, define the source file's log level expression,
1112 `BT_LOG_OUTPUT_LEVEL`. This expression is evaluated for each
1113 <<comp-logging-statements,logging statement>> to know the current
1114 <<run-time-log-level,run-time log level>>.
1116 For a component class file, it is usually a member of a local component
1117 private structure variable:
1121 #define BT_LOG_OUTPUT_LEVEL (my_comp->log_level)
1124 . Below the line above, define `BT_COMP_LOG_SELF_COMP` to an expression
1125 which, evaluated in the context of the
1126 <<comp-logging-statements,logging statements>>, evaluates to the self
1127 component address (`+bt_self_component *+`) of the component.
1129 This is usually a member of a local component private structure
1134 #define BT_COMP_LOG_SELF_COMP (my_comp->self_comp)
1137 . Include `"logging/comp-logging.h"`:
1141 #include "logging/comp-logging.h"
1144 . In the component initialization method, make sure to set the
1145 component private structure's log level member to the initial
1146 component's log level:
1151 bt_logging_level log_level;
1156 bt_self_component_status my_comp_init(
1157 bt_self_component_source *self_comp_src,
1158 bt_value *params, void *init_method_data)
1160 struct my_comp *my_comp = g_new0(struct my_comp, 1);
1161 bt_self_component *self_comp =
1162 bt_self_component_source_as_self_component(self_comp_src);
1163 const bt_component *comp = bt_self_component_as_component(self_comp);
1166 my_comp->log_level = bt_component_get_logging_level(comp);
1172 . In the file, instrument your code with the
1173 <<comp-logging-statements,component logging statement macros>>.
1175 [[logging-instrument-h-file-compcls]]
1176 ==== Instrument a component class {c-cpp} header file
1178 To instrument a component class {c-cpp} header file (`.h`/`.hpp`), if
1179 you have `static inline` functions in it:
1181 . Do not include `"logging/comp-logging.h"`!
1183 . Require that component logging be enabled:
1187 /* Protection: this file uses BT_COMP_LOG*() macros directly */
1188 #ifndef BT_COMP_LOG_SUPPORTED
1189 # error Please include "logging/comp-logging.h" before including this file.
1193 . In the file, instrument your code with the
1194 <<comp-logging-statements,component logging statement macros>>.
1196 [[choose-a-logging-tag]]
1197 ==== Choose a logging tag
1199 Each logging-enabled {c-cpp} source file must define `BT_LOG_TAG` to a
1200 logging tag. A logging tag is a namespace to identify the logging
1201 messages of this specific source file.
1203 In general, a logging tag name _must_ be only uppercase letters, digits,
1204 and the `-`, `.`, and `/` characters.
1206 Use `/` to show the subsystem to source file hierarchy.
1208 For the {bt2} library, start with `LIB/`.
1210 For the CTF writer library, start with `CTF-WRITER/`.
1212 For component classes, use:
1215 `PLUGIN/__CCTYPE__.__PNAME__.__CCNAME__[/__FILE__]`
1220 Component class's type (`SRC`, `FLT`, or `SINK`).
1226 Component class's name.
1229 Additional information to specify the source file name or module.
1231 For plugins (files common to many component classes), use:
1234 `PLUGIN/__PNAME__[/__FILE__]`
1242 Additional information to specify the source file name or module.
1244 [[choose-a-log-level]]
1245 ==== Choose a log level
1247 Choosing the appropriate level for your logging statement is very
1250 [options="header,autowidth",cols="1,2,3a,4"]
1252 |Log level |Description |Use cases |Expected impact on performance
1256 The program, library, or plugin cannot continue to work in this
1257 condition: it must be terminated immediately.
1259 A _FATAL_-level logging statement should always be followed by
1262 * Unexpected return values from system calls.
1263 * Logic error in internal code, for example an unexpected value in a
1265 * Failed assertion (within `BT_ASSERT()`).
1266 * Unsatisfied library precondition (within `BT_ASSERT_PRE()` or
1267 `BT_ASSERT_PRE_DEV()`).
1268 * Unsatisfied library postcondition (within `BT_ASSERT_POST()` or
1269 `BT_ASSERT_POST_DEV()`).
1270 |Almost none: always enabled.
1274 An important error which is somewhat not fatal, that is, the program,
1275 library, or plugin can continue to work after this, but you judge that
1276 it should be reported to the user.
1278 Usually, the program cannot recover from such an error, but it can at
1281 * Memory allocation errors.
1282 * Wrong component initialization parameters.
1283 * Corrupted, unrecoverable trace data.
1284 * Failed to perform an operation which should work considering the
1285 implementation and the satisfied preconditions. For example, the
1286 failure to create an empty object (no parameters): most probably
1287 failed internally because of an allocation error.
1288 * Almost any error in terminal elements: CLI and plugins.
1289 |Almost none: always enabled.
1293 An error which still allows the execution to continue, but you judge
1294 that it should be reported to the user.
1296 _WARNING_-level logging statements are for any error or weird action
1297 that is directly or indirectly caused by the user, often through some
1298 bad input data. For example, not having enough memory is considered
1299 beyond the user's control, so we always log memory errors with an
1300 _ERROR_ level (not _FATAL_ because we usually don't abort in this
1303 * Missing data within something that is expected to have it, but there's
1305 * Invalid file, but recoverable/fixable.
1306 |Almost none: always enabled.
1310 Any useful information which a non-developer user would possibly
1313 Anything logged with this level must _not_ happen repetitively on the
1314 fast path, that is, nothing related to each message, for example. This
1315 level is used for sporadic and one-shot events.
1317 * CLI or component configuration report.
1318 * Successful plugin, component, or message iterator initialization.
1319 * In the library: anything related to plugins, graphs, component
1320 classes, components, message iterators, connections, and ports which
1321 is not on the fast path.
1322 * Successful connection to or disconnection from another system.
1323 * An _optional_ subsystem cannot be loaded.
1324 * An _optional_ field/datum cannot be found.
1326 Very little: always enabled.
1330 Something that only {bt2} developers would be interested into,
1331 which can occur on the fast path, but not more often than once per
1334 The _DEBUG_ level is the default <<build-time-log-level,build-time log
1335 level>> as, since it's not _too_ verbose, the performance is similar to
1338 * Object construction and destruction.
1339 * Object recycling (except fields).
1340 * Object copying (except fields and values).
1341 * Object freezing (whatever the type, as freezing only occurs in
1343 * Object interruption.
1344 * Calling user methods and logging the result.
1345 * Setting object properties (except fields and values).
1347 Noticeable, but not as much as the _TRACE_ level: could be executed
1348 in production if you're going to need a thorough log for support
1349 tickets without having to rebuild the project.
1353 Low-level debugging context information (anything that does not fit the
1354 other log levels). More appropriate for tracing in general.
1356 * Reference count change.
1357 * Fast path, low level state machine's state change.
1358 * Get or set an object's property.
1359 * Object comparison's intermediate results.
1360 |Huge: not executed in production.
1365 Make sure not to use a _WARNING_ (or higher) log level when the
1366 condition leading to the logging statement can occur under normal
1369 For example, a public function to get some object or
1370 property from an object by name or key that fails to find the value is
1371 not a warning scenario: the user could legitimately use this function to
1372 check if the name/key exists in the object. In this case, use the
1373 _TRACE_ level (or do not log at all).
1377 ==== Write an appropriate message
1379 Follow those rules when you write a logging statement's message:
1381 * Use an English sentence which starts with a capital letter.
1383 * Start the sentence with the appropriate verb tense depending on the
1384 context. For example:
1387 ** Beginning of operation (present continuous): _Creating ..._,
1388 _Copying ..._, _Serializing ..._, _Freezing ..._, _Destroying ..._
1389 ** End of operation (simple past): _Created ..._, _Successfully created ..._,
1390 _Failed to create ..._, _Set ..._ (simple past of _to set_ which is
1394 For warning and error messages, you can start the message with _Cannot_
1395 or _Failed to_ followed by a verb if it's appropriate.
1397 * Do not include the log level in the message itself. For example,
1398 do not start the message with _Error while_ or _Warning:_.
1400 * Do not put newlines, tabs, or other special characters in the message,
1401 unless you want to log a string with such characters. Note that
1402 multiline logging messages can be hard to parse, analyze, and filter,
1403 however, so prefer multiple logging statements over a single statement
1406 * **If there are fields that your logging statement must record**,
1407 follow the message with `:` followed by a space, then with the list of
1408 fields (more about this below). If there are no fields, end the
1409 sentence with a period.
1411 The statement's fields _must_ be a comma-separated list of
1412 `__name__=__value__` tokens. Keep `__name__` as simple as possible; use
1413 kebab case if possible. If `__value__` is a non-alphanumeric string, put
1414 it between double quotes (`"%s"` specifier). Always use the `PRId64` and
1415 `PRIu64` specifiers to log an `int64_t` or an `uint64_t` value. Use `%d`
1416 to log a boolean value.
1420 "Cannot read stream data for indexing: path=\"%s\", name=\"%s\", "
1421 "stream-id=%" PRIu64 ", stream-fd=%d, "
1422 "index=%" PRIu64 ", status=%s, is-mapped=%d"
1424 By following a standard format for the statement fields, it is easier to
1425 use tools like https://www.elastic.co/products/logstash[Logstash] or
1426 even https://www.splunk.com/[Splunk] to split fields and analyze logs.
1428 Prefer the following suffixes in field names:
1430 [options="header,autowidth"]
1432 |Field name suffix |Description |Format specifier
1434 |`-addr` |Memory address |`%p`
1435 |`-fd` |File descriptor |`%d`
1436 |`-fp` |File stream (`+FILE *+`) |`%p`
1437 |`-id` |Object's ID |`%" PRIu64 "`
1438 |`-index` |Index |`%" PRIu64 "`
1439 |`-name` |Object's name |`\"%s\"`
1444 The log is printed to the standard error stream. A log line contains the
1445 time, the process and thread IDs, the <<log-levels,log level>>, the
1446 <<choose-a-logging-tag,logging tag>>, the source's function name, file
1447 name and line number, and the <<message,message>>.
1449 When {bt2} supports terminal color codes (depends on the
1450 `BABELTRACE_TERM_COLOR` environment variable's value and what the
1451 standard output and error streams are plugged into), _INFO_-level lines
1452 are blue, _WARNING_-level lines are yellow, and _ERROR_-level and
1453 _FATAL_-level lines are red.
1458 05-11 00:58:03.691 23402 23402 D VALUES bt_value_destroy@values.c:498 Destroying value: addr=0xb9c3eb0
1461 You can easily filter the log with `grep` or `ag`. For example, to keep
1462 only the _DEBUG_-level logging messages that the `FIELD-CLASS` module
1466 $ babeltrace2 --log-level=D /path/to/trace |& ag 'D FIELD-CLASS'
1471 To use Valgrind on an application (for example, the CLI or a test) which
1472 loads libbabeltrace2, use:
1475 $ G_SLICE=always-malloc G_DEBUG=gc-friendly PYTHONMALLOC=malloc \
1476 LIBBABELTRACE2_NO_DLCLOSE=1 valgrind --leak-check=full app
1479 `G_SLICE=always-malloc` and `G_DEBUG=gc-friendly` is for GLib and
1480 `PYTHONMALLOC=malloc` is for the Python interpreter, if it is used by
1481 the Python plugin provider (Valgrind will probably show a lot of errors
1482 which originate from the Python interpreter anyway).
1484 `LIBBABELTRACE2_NO_DLCLOSE=1` makes libbabeltrace2 not close the shared
1485 libraries (plugins) which it loads. You need this to see the appropriate
1486 backtrace when Valgrind shows errors.
1493 Running `make check` in the build directory (regardless of whether the build is
1494 in-tree or out-of-tree) automatically sets up the appropriate environment for
1495 tests to run in, so nothing more is needed.
1497 If building in-tree, you can run single tests from the tree directly:
1500 $ ./tests/plugins/sink.text.pretty/test_enum
1503 If building out-of-tree, you can get the appropriate environment by sourcing
1504 the `tests/utils/env.sh` file residing in the build directory against which you
1508 $ source /path/to/my/build/tests/utils/env.sh
1509 $ ./tests/plugins/sink.text.pretty/test_enum
1514 You can use the `tests/utils/run_python_bt2` script to run any command
1515 within an environment making the build's `bt2` Python package available.
1517 `run_python_bt2` uses <<test-env,`utils.sh`>> which needs to know the
1518 build directory, so make sure you set the `BT_TESTS_BUILDDIR`
1519 environment variable correctly _if you build out of tree_, for example:
1522 $ export BT_TESTS_BUILDDIR=/path/to/build/babeltrace/tests
1525 You can run any command which needs the `bt2` Python package through
1526 `run_python_bt2`, for example:
1529 $ ./tests/utils/run_python_bt2 ipython3
1534 All test scripts output the test results following the
1535 https://testanything.org/[Test Anything Protocol] (TAP) format.
1537 The TAP format has two mechanisms to print additional information about
1540 * Print a line starting with `#` to the standard output.
1542 This is usually done with the `diag()` C function or the `diag` shell
1545 * Print to the standard error.
1549 The `bt2` Python package tests are located in
1550 `tests/bindings/python/bt2`.
1552 ==== Python test runner
1554 `tests/utils/python/testrunner.py` is {bt2}'s Python test runner
1555 which loads Python files containing unit tests, finds all the test
1556 cases, and runs the tests, producing a TAP report.
1558 You can see the test runner command's help with:
1561 $ python3 ./tests/utils/python/testrunner.py --help
1564 By default, the test runner reports failing tests (TAP's `not{nbsp}ok`
1565 line), but continues to run other tests. You can use the `--failfast`
1566 option to make the test runner fail as soon as a test fails.
1570 To run all the `bt2` Python package tests:
1575 $ ./tests/utils/run_python_bt2 ./tests/bindings/python/bt2/test_python_bt2
1581 $ ./tests/utils/run_python_bt2 python3 ./tests/utils/python/testrunner.py \
1582 ./tests/bindings/python/bt2/ -p '*.py'
1585 To run **all the tests** in a test module (for example,
1591 $ ./tests/utils/run_python_bt2 python3 ./tests/utils/python/testrunner.py \
1592 ./tests/bindings/python/bt2 -t test_value
1595 To run a **specific test case** (for example, `RealValueTestCase` within
1601 $ ./tests/utils/run_python_bt2 python3 ./tests/utils/python/testrunner.py \
1602 ./tests/bindings/python/bt2/ -t test_value.RealValueTestCase
1605 To run a **specific test** (for example,
1606 `RealValueTestCase.test_assign_pos_int` within `test_value.py`):
1611 $ ./tests/utils/run_python_bt2 python3 ./tests/utils/python/testrunner.py \
1612 ./tests/bindings/python/bt2/ -t test_value.RealValueTestCase.test_assign_pos_int
1617 Some parts of {bt2} are written in {cpp}.
1619 This section shows what's important to know about {cpp} to contribute
1624 {bt2} only has {cpp} sources for _internal_ code.
1626 In other words, libbabeltrace2 _must_ expose a pure C99 API to preserve
1627 ABI compatibility over time.
1630 === Standard and dependencies
1632 The {bt2} project is configured to use the {cpp11} standard.
1634 {cpp11} makes it possible to build {bt2} with a broad range of
1635 compilers, from GCC{nbsp}4.8 and Clang{nbsp}3.3.
1637 === Automake/Libtool requirements
1639 To add a {cpp} source file to a part of the project, use the `.cpp`
1640 extension and add it to the list of source files in `Makefile.am` as
1643 If a program or a shared library has a direct {cpp} source file, then
1644 Libtool uses the {cpp} linker to create the result, dynamically
1645 linking important runtime libraries such as libstdc++ and libgcc_s.
1647 Because a Libtool _convenience library_ is just an archive (`.a`), it's
1648 _not_ dynamically linked to runtime libraries, even if one of its direct
1649 sources is a {cpp} file. This means that for each program or shared
1650 library named `my_target` in `Makefile.am` which is linked to a
1651 convenience library having {cpp} sources (recursively), you _must_ do
1654 * Have at least one direct {cpp} source file in the
1655 `+*_my_target_SOURCES+` list.
1660 nodist_EXTRA_my_target_SOURCES = dummy.cpp
1664 https://www.gnu.org/software/automake/manual/automake.html#Libtool-Convenience-Libraries[Libtool
1665 Convenience Libraries] to learn more.
1667 For a given program or library, you _cannot_ have a C{nbsp}file and a
1668 {cpp}{nbsp}file having the same name, for example `list.c` and
1673 ==== Whitespaces, indentation, and line breaks
1675 All the project's {cpp} files follow the
1676 https://clang.llvm.org/docs/ClangFormat.html[clang-format]
1677 https://clang.llvm.org/docs/ClangFormatStyleOptions.html[style] of the
1678 `.clang-format` file for whitespaces, indentation, and line breaks.
1680 You _must_ format modified and new {cpp} files with clang-format before
1681 you create a contribution patch.
1683 You need clang-format{nbsp}13 to use the project's `.clang-format` file.
1685 To automatically format all the project's {cpp} files, run:
1688 $ ./tools/format-cpp
1691 Use the `FORMATTER` environment variable to override the default
1692 formatter (`clang-format{nbsp}-i`):
1695 $ FORMATTER='clang-format-10 -i' ./tools/format-cpp
1700 * Use camel case with a lowercase first letter for:
1701 ** Variable names: `size`, `objSize`.
1702 ** Function/method names: `size()`, `formatAndPrint()`.
1704 * Use camel case with an uppercase first letter for:
1705 ** Types: `Pistachio`, `NutManager`.
1706 ** Template parameters: `PlanetT`, `TotalSize`.
1708 * Use snake case with uppercase letters for:
1709 ** Definition/macro names: `MARK_AS_UNUSED()`, `SOME_FEATURE_EXISTS`.
1710 ** Enumerators: `Type::SIGNED_INT`, `Scope::FUNCTION`.
1712 * Use only lowercase letters and digits for namespaces: `mylib`, `bt2`.
1714 * Use the suffix `T` for type template parameters:
1718 template <typename NameT, typename ItemT>
1721 * Name a template parameter pack `Args`.
1725 template <typename NameT, typename... Args>
1728 * Use an underscore prefix for private and protected methods and member
1729 type names: `_tryConnect()`, `_NodeType`.
1731 * Use the prefix `_m` for private and protected member variable names:
1732 `_mLogger`, `_mSize`, `_mFieldClass`.
1734 * Name setters and getters like the property name, without `set` and
1737 * Use the `is` or `has` prefix, if possible, to name the functions which
1740 === Coding convention
1742 In general, the project's contributors make an effort to follow,
1746 https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md[{cpp} Core Guidelines].
1749 "`https://www.oreilly.com/library/view/effective-modern-c/9781491908419/[Effective Modern {cpp}]`".
1751 Here are a few important reminders:
1753 * Namespace your code.
1755 * Create one header/source file pair per class when possible.
1757 For a class named `MyClass`, name the corresponding files `my-class.hpp`
1760 * When defining a class, put constructors as the first methods, whatever
1761 their access (public/protected/private), then the destructor, and then
1764 * Declare variables as close to where they are used as possible.
1766 * Use `auto` when possible.
1768 * Use `const` as much as possible, even for pointer
1769 (`+const char* const+`) and numeric values (`const unsigned int`)
1770 which never need to change.
1772 * Implement simple setters, getters, and one-liners in header files and
1773 everything else that's not a template in source files.
1775 * Make methods `const noexcept` or `const` as much as possible.
1777 * Make constructors `explicit` unless you really need an implicit
1778 constructor (which is rare).
1780 * Use `std::unique_ptr` to manage memory when possible.
1782 However, use references (`+*my_unique_ptr+`) and raw pointers
1783 (`+my_unique_ptr.get()+`) when not transferring ownership.
1785 * Use `nullptr`, not `NULL` nor 0.
1787 * Return by value (rvalue) instead of by output parameter (non-const
1788 lvalue reference), even complex objects, unless you can prove that the
1789 performance is improved when returning by parameter.
1791 * For a function parameter or a return value of which the type needs to
1792 be a reference or pointer, use:
1794 If the value is mandatory:::
1796 If the value is optional:::
1799 * Don't use `+std::move()+` when you already have an rvalue, which
1801 ** Don't write `+return std::move(...);+` as this can interfere with
1803 ** Don't use `+std::move()+` with a function call
1804 (`+std::move(func())+`).
1806 * For each possible move/copy constructor or assignment operator, do one
1808 ** Write a custom one.
1809 ** Mark it as defaulted (`default`)
1810 ** Mark it as deleted (`delete`).
1812 * Use scoped enumerations (`+enum class+`).
1814 * Mark classes known to be final with the `final` keyword.
1816 * Use type aliases (`using`), not type definitions (`typedef`).
1818 * Use anonymous namespaces for local functions instead of `static`.
1820 * Don't pollute the global namespace:
1821 ** Don't use `using namespace xyz` anywhere.
1822 ** Use only namespace aliases in source files (`.cpp`), trying to
1823 use them in the smallest possible scope (function, or even smaller).
1825 * Return a structure with named members instead of a generic container
1826 such as `std::pair` or `std::tuple`.
1828 * When a class inherits a base class with virtual methods, use the
1829 `override` keyword to mark overridden virtual methods, and do not use
1830 the `virtual` keyword again.
1832 * Define overloaded operators only if their meaning is obvious,
1833 unsurprising, and consistent with the corresponding built-in
1836 For example, use `+|+` as a bitwise- or logical-or, not as a shell-style
1839 * Use RAII wrappers when managing system resources or interacting with
1842 In other words, don't rely on ``goto``s and error labels to clean up as
1843 you would do in{nbsp}C.
1847 * Throw an exception when there's an unexpected, exceptional condition,
1848 https://isocpp.org/wiki/faq/exceptions#ctors-can-throw[including from
1849 a constructor], instead of returning a status code.
1851 * Accept a by-value parameter and move it (when it's moveable) when you
1852 intend to copy it anyway.
1854 You can do this with most STL containers.
1860 void Obj::doSomething(std::string str)
1862 _mName = std::move(str);
1869 This example shows a {cpp} header which follows the {bt2} {cpp} coding
1875 * SPDX-License-Identifier: MIT
1877 * Copyright 2020 Harry Burnett <hburnett@reese.choco>
1880 #ifndef BABELTRACE_BABY_HPP
1881 #define BABELTRACE_BABY_HPP
1884 #include <unordered_set>
1892 * A baby is a little human.
1894 class Baby : public Human
1897 using Toys = std::unordered_set<Toy>;
1907 explicit Baby(const Toys& toys);
1908 Baby(const Baby&) = delete;
1909 Baby(Baby&&) = delete;
1910 Baby& operator=(const Baby&) = delete;
1911 Baby& operator=(Baby&&) = delete;
1914 explicit Baby(Gender initialGender = Gender::UNKNOWN);
1918 * Eats `weight` grams of food.
1920 void eat(unsigned long weight);
1923 * Sleeps for `duration` seconds.
1925 void sleep(double duration);
1928 * Sets this baby's name to `name`.
1930 void name(std::string name)
1932 _mName = std::move(name);
1938 const std::string& name() const noexcept
1944 void _addTeeth(unsigned long index);
1945 void _grow(double size) override;
1948 std::string _mName {"Paul"};
1954 #endif // BABELTRACE_BABY_HPP