diff options
Diffstat (limited to 'trace2.h')
| -rw-r--r-- | trace2.h | 124 |
1 files changed, 102 insertions, 22 deletions
@@ -1,6 +1,40 @@ #ifndef TRACE2_H #define TRACE2_H +/** + * The Trace2 API can be used to print debug, performance, and telemetry + * information to stderr or a file. The Trace2 feature is inactive unless + * explicitly enabled by enabling one or more Trace2 Targets. + * + * The Trace2 API is intended to replace the existing (Trace1) + * printf-style tracing provided by the existing `GIT_TRACE` and + * `GIT_TRACE_PERFORMANCE` facilities. During initial implementation, + * Trace2 and Trace1 may operate in parallel. + * + * The Trace2 API defines a set of high-level messages with known fields, + * such as (`start`: `argv`) and (`exit`: {`exit-code`, `elapsed-time`}). + * + * Trace2 instrumentation throughout the Git code base sends Trace2 + * messages to the enabled Trace2 Targets. Targets transform these + * messages content into purpose-specific formats and write events to + * their data streams. In this manner, the Trace2 API can drive + * many different types of analysis. + * + * Targets are defined using a VTable allowing easy extension to other + * formats in the future. This might be used to define a binary format, + * for example. + * + * Trace2 is controlled using `trace2.*` config values in the system and + * global config files and `GIT_TRACE2*` environment variables. Trace2 does + * not read from repo local or worktree config files or respect `-c` + * command line config settings. + * + * For more info about: trace2 targets, conventions for public functions and + * macros, trace2 target formats and examples on trace2 API usage refer to + * Documentation/technical/api-trace2.txt + * + */ + struct child_process; struct repository; struct json_writer; @@ -39,7 +73,12 @@ void trace2_initialize_clock(void); /* * Initialize TRACE2 tracing facility if any of the builtin TRACE2 * targets are enabled in the system config or the environment. - * Emits a 'version' event. + * This includes setting up the Trace2 thread local storage (TLS). + * Emits a 'version' message containing the version of git + * and the Trace2 protocol. + * + * This function should be called from `main()` as early as possible in + * the life of the process after essential process initialization. * * Cleanup/Termination is handled automatically by a registered * atexit() routine. @@ -49,7 +88,7 @@ void trace2_initialize_fl(const char *file, int line); #define trace2_initialize() trace2_initialize_fl(__FILE__, __LINE__) /* - * Return true if trace2 is enabled. + * Return 1 if trace2 is enabled (at least one target is active). */ int trace2_is_enabled(void); @@ -114,7 +153,8 @@ void trace2_cmd_mode_fl(const char *file, int line, const char *mode); #define trace2_cmd_mode(sv) trace2_cmd_mode_fl(__FILE__, __LINE__, (sv)) /* - * Emit an 'alias' expansion event. + * Emits an "alias" message containing the alias used and the argument + * expansion. */ void trace2_cmd_alias_fl(const char *file, int line, const char *alias, const char **argv); @@ -123,7 +163,7 @@ void trace2_cmd_alias_fl(const char *file, int line, const char *alias, trace2_cmd_alias_fl(__FILE__, __LINE__, (alias), (argv)) /* - * Emit one or more 'def_param' events for "interesting" configuration + * Emit one or more 'def_param' events for "important" configuration * settings. * * Use the TR2_SYSENV_CFG_PARAM setting to register a comma-separated @@ -144,7 +184,7 @@ void trace2_cmd_list_config_fl(const char *file, int line); /* * Emit a "def_param" event for the given config key/value pair IF - * we consider the key to be "interesting". + * we consider the key to be "important". * * Use this for new/updated config settings created/updated after * trace2_cmd_list_config() is called. @@ -155,20 +195,34 @@ void trace2_cmd_set_config_fl(const char *file, int line, const char *key, #define trace2_cmd_set_config(k, v) \ trace2_cmd_set_config_fl(__FILE__, __LINE__, (k), (v)) -/* - * Emit a 'child_start' event prior to spawning a child process. +/** + * Emits a "child_start" message containing the "child-id", + * "child-argv", and "child-classification". * * Before calling optionally set "cmd->trace2_child_class" to a string * describing the type of the child process. For example, "editor" or * "pager". + * + * This function assigns a unique "child-id" to `cmd->trace2_child_id`. + * This field is used later during the "child_exit" message to associate + * it with the "child_start" message. + * + * This function should be called before spawning the child process. */ void trace2_child_start_fl(const char *file, int line, struct child_process *cmd); #define trace2_child_start(cmd) trace2_child_start_fl(__FILE__, __LINE__, (cmd)) -/* - * Emit a 'child_exit' event after the child process completes. +/** + * Emits a "child_exit" message containing the "child-id", + * the child's elapsed time and exit-code. + * + * The reported elapsed time includes the process creation overhead and + * time spend waiting for it to exit, so it may be slightly longer than + * the time reported by the child itself. + * + * This function should be called after reaping the child process. */ void trace2_child_exit_fl(const char *file, int line, struct child_process *cmd, int child_exit_code); @@ -176,21 +230,22 @@ void trace2_child_exit_fl(const char *file, int line, struct child_process *cmd, #define trace2_child_exit(cmd, code) \ trace2_child_exit_fl(__FILE__, __LINE__, (cmd), (code)) -/* +/** * Emit an 'exec' event prior to calling one of exec(), execv(), * execvp(), and etc. On Unix-derived systems, this will be the * last event emitted for the current process, unless the exec * fails. On Windows, exec() behaves like 'child_start' and a * waitpid(), so additional events may be emitted. * - * Returns the "exec_id". + * Returns a unique "exec-id". This value is used later + * if the exec() fails and a "exec-result" message is necessary. */ int trace2_exec_fl(const char *file, int line, const char *exe, const char **argv); #define trace2_exec(exe, argv) trace2_exec_fl(__FILE__, __LINE__, (exe), (argv)) -/* +/** * Emit an 'exec_result' when possible. On Unix-derived systems, * this should be called after exec() returns (which only happens * when there is an error starting the new process). On Windows, @@ -226,11 +281,12 @@ void trace2_thread_exit_fl(const char *file, int line); #define trace2_thread_exit() trace2_thread_exit_fl(__FILE__, __LINE__) /* - * Emit a 'param' event. + * Emits a "def_param" message containing a key/value pair. * - * Write a "<param> = <value>" pair describing some aspect of the - * run such as an important configuration setting or command line - * option that significantly changes command behavior. + * This message is intended to report some global aspect of the current + * command, such as a configuration setting or command line switch that + * significantly affects program performance or behavior, such as + * `core.abbrev`, `status.showUntrackedFiles`, or `--no-ahead-behind`. */ void trace2_def_param_fl(const char *file, int line, const char *param, const char *value); @@ -243,18 +299,35 @@ void trace2_def_param_fl(const char *file, int line, const char *param, * a trace2-repo-id to be used in subsequent activity events. * * Emits a 'worktree' event for this repo instance. + * + * Region and data messages may refer to this repo-id. + * + * The main/top-level repository will have repo-id value 1 (aka "r1"). + * + * The repo-id field is in anticipation of future in-proc submodule + * repositories. */ void trace2_def_repo_fl(const char *file, int line, struct repository *repo); #define trace2_def_repo(repo) trace2_def_repo_fl(__FILE__, __LINE__, repo) -/* +/** * Emit a 'region_enter' event for <category>.<label> with optional * repo-id and printf message. * - * Enter a new nesting level on the current thread and remember the - * current time. This controls the indenting of all subsequent events - * on this thread. + * This function pushes a new region nesting stack level on the current + * thread and starts a clock for the new stack frame. + * + * The `category` field is an arbitrary category name used to classify + * regions by feature area, such as "status" or "index". At this time + * it is only just printed along with the rest of the message. It may + * be used in the future to filter messages. + * + * The `label` field is an arbitrary label used to describe the activity + * being started, such as "read_recursive" or "do_read_index". + * + * The `repo` field, if set, will be used to get the "repo-id", so that + * recursive oerations can be attributed to the correct repository. */ void trace2_region_enter_fl(const char *file, int line, const char *category, const char *label, const struct repository *repo, ...); @@ -289,12 +362,17 @@ void trace2_region_enter_printf(const char *category, const char *label, /* clang-format on */ #endif -/* +/** * Emit a 'region_leave' event for <category>.<label> with optional * repo-id and printf message. * * Leave current nesting level and report the elapsed time spent * in this nesting level. + * + * The `category`, `label`, and `repo` fields are the same as + * trace2_region_enter_fl. The `category` and `label` do not + * need to match the corresponding "region_enter" message, + * but it makes the data stream easier to understand. */ void trace2_region_leave_fl(const char *file, int line, const char *category, const char *label, const struct repository *repo, ...); @@ -329,10 +407,12 @@ void trace2_region_leave_printf(const char *category, const char *label, /* clang-format on */ #endif -/* +/** * Emit a key-value pair 'data' event of the form <category>.<key> = <value>. * This event implicitly contains information about thread, nesting region, * and optional repo-id. + * This could be used to print the number of files in a directory during + * a multi-threaded recursive tree walk. * * On event-based TRACE2 targets, this generates a 'data' event suitable * for post-processing. On printf-based TRACE2 targets, this is converted |