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Diffstat (limited to 'third_party/git/Documentation/technical/api-trace2.txt')
| -rw-r--r-- | third_party/git/Documentation/technical/api-trace2.txt | 282 |
1 files changed, 245 insertions, 37 deletions
diff --git a/third_party/git/Documentation/technical/api-trace2.txt b/third_party/git/Documentation/technical/api-trace2.txt index 4f07ceadcb3f..71eb081fed25 100644 --- a/third_party/git/Documentation/technical/api-trace2.txt +++ b/third_party/git/Documentation/technical/api-trace2.txt @@ -128,7 +128,7 @@ yields ------------ $ cat ~/log.event -{"event":"version","sid":"sid":"20190408T191610.507018Z-H9b68c35f-P000059a8","thread":"main","time":"2019-01-16T17:28:42.620713Z","file":"common-main.c","line":38,"evt":"2","exe":"2.20.1.155.g426c96fcdb"} +{"event":"version","sid":"sid":"20190408T191610.507018Z-H9b68c35f-P000059a8","thread":"main","time":"2019-01-16T17:28:42.620713Z","file":"common-main.c","line":38,"evt":"1","exe":"2.20.1.155.g426c96fcdb"} {"event":"start","sid":"20190408T191610.507018Z-H9b68c35f-P000059a8","thread":"main","time":"2019-01-16T17:28:42.621027Z","file":"common-main.c","line":39,"t_abs":0.001173,"argv":["git","version"]} {"event":"cmd_name","sid":"20190408T191610.507018Z-H9b68c35f-P000059a8","thread":"main","time":"2019-01-16T17:28:42.621122Z","file":"git.c","line":432,"name":"version","hierarchy":"version"} {"event":"exit","sid":"20190408T191610.507018Z-H9b68c35f-P000059a8","thread":"main","time":"2019-01-16T17:28:42.621236Z","file":"git.c","line":662,"t_abs":0.001227,"code":0} @@ -142,9 +142,10 @@ system or global config value to one of the following: include::../trace2-target-values.txt[] -When trace files are written to a target directory, they will be named according -to the last component of the SID (optionally followed by a counter to avoid -filename collisions). +If the target already exists and is a directory, the traces will be +written to files (one per process) underneath the given directory. They +will be named according to the last component of the SID (optionally +followed by a counter to avoid filename collisions). == Trace2 API @@ -178,7 +179,7 @@ describe the simplified forms. == Public API -All Trace2 API functions send a message to all of the active +All Trace2 API functions send a messsage to all of the active Trace2 Targets. This section describes the set of available messages. @@ -188,36 +189,261 @@ purposes. === Basic Command Messages These are concerned with the lifetime of the overall git process. -e.g: `void trace2_initialize_clock()`, `void trace2_initialize()`, -`int trace2_is_enabled()`, `void trace2_cmd_start(int argc, const char **argv)`. + +`void trace2_initialize_clock()`:: + + Initialize the Trace2 start clock and nothing else. This should + be called at the very top of main() to capture the process start + time and reduce startup order dependencies. + +`void trace2_initialize()`:: + + Determines if any Trace2 Targets should be enabled and + initializes the Trace2 facility. This includes setting up the + Trace2 thread local storage (TLS). ++ +This function 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. + +`int trace2_is_enabled()`:: + + Returns 1 if Trace2 is enabled (at least one target is + active). + +`void trace2_cmd_start(int argc, const char **argv)`:: + + Emits a "start" message containing the process command line + arguments. + +`int trace2_cmd_exit(int exit_code)`:: + + Emits an "exit" message containing the process exit-code and + elapsed time. ++ +Returns the exit-code. + +`void trace2_cmd_error(const char *fmt, va_list ap)`:: + + Emits an "error" message containing a formatted error message. + +`void trace2_cmd_path(const char *pathname)`:: + + Emits a "cmd_path" message with the full pathname of the + current process. === Command Detail Messages These are concerned with describing the specific Git command after the command line, config, and environment are inspected. -e.g: `void trace2_cmd_name(const char *name)`, -`void trace2_cmd_mode(const char *mode)`. + +`void trace2_cmd_name(const char *name)`:: + + Emits a "cmd_name" message with the canonical name of the + command, for example "status" or "checkout". + +`void trace2_cmd_mode(const char *mode)`:: + + Emits a "cmd_mode" message with a qualifier name to further + describe the current git command. ++ +This message is intended to be used with git commands having multiple +major modes. For example, a "checkout" command can checkout a new +branch or it can checkout a single file, so the checkout code could +emit a cmd_mode message of "branch" or "file". + +`void trace2_cmd_alias(const char *alias, const char **argv_expansion)`:: + + Emits an "alias" message containing the alias used and the + argument expansion. + +`void trace2_def_param(const char *parameter, const char *value)`:: + + Emits a "def_param" message containing a key/value pair. ++ +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_cmd_list_config()`:: + + Emits a "def_param" messages for "important" configuration + settings. ++ +The environment variable `GIT_TRACE2_CONFIG_PARAMS` or the `trace2.configParams` +config value can be set to a +list of patterns of important configuration settings, for example: +`core.*,remote.*.url`. This function will iterate over all config +settings and emit a "def_param" message for each match. + +`void trace2_cmd_set_config(const char *key, const char *value)`:: + + Emits a "def_param" message for a new or updated key/value + pair IF `key` is considered important. ++ +This is used to hook into `git_config_set()` and catch any +configuration changes and update a value previously reported by +`trace2_cmd_list_config()`. + +`void trace2_def_repo(struct repository *repo)`:: + + Registers a repository with the Trace2 layer. Assigns a + unique "repo-id" to `repo->trace2_repo_id`. ++ +Emits a "worktree" messages containing the repo-id and the worktree +pathname. ++ +Region and data messages (described later) 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. === Child Process Messages These are concerned with the various spawned child processes, including shell scripts, git commands, editors, pagers, and hooks. -e.g: `void trace2_child_start(struct child_process *cmd)`. +`void trace2_child_start(struct child_process *cmd)`:: + + Emits a "child_start" message containing the "child-id", + "child-argv", and "child-classification". ++ +Before calling this, set `cmd->trace2_child_class` to a name +describing the type of child process, for example "editor". ++ +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_exit(struct child_proess *cmd, int child_exit_code)`:: + + 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. + +`int trace2_exec(const char *exe, const char **argv)`:: + + Emits a "exec" message containing the "exec-id" and the + argv of the new process. ++ +This function should be called before calling one of the `exec()` +variants, such as `execvp()`. ++ +This function returns a unique "exec-id". This value is used later +if the exec() fails and a "exec-result" message is necessary. + +`void trace2_exec_result(int exec_id, int error_code)`:: + + Emits a "exec_result" message containing the "exec-id" + and the error code. ++ +On Unix-based systems, `exec()` does not return if successful. +This message is used to indicate that the `exec()` failed and +that the current program is continuing. === Git Thread Messages These messages are concerned with Git thread usage. -e.g: `void trace2_thread_start(const char *thread_name)`. +`void trace2_thread_start(const char *thread_name)`:: + + Emits a "thread_start" message. ++ +The `thread_name` field should be a descriptive name, such as the +unique name of the thread-proc. A unique "thread-id" will be added +to the name to uniquely identify thread instances. ++ +Region and data messages (described later) may refer to this thread +name. ++ +This function must be called by the thread-proc of the new thread +(so that TLS data is properly initialized) and not by the caller +of `pthread_create()`. + +`void trace2_thread_exit()`:: + + Emits a "thread_exit" message containing the thread name + and the thread elapsed time. ++ +This function must be called by the thread-proc before it returns +(so that the coorect TLS data is used and cleaned up. It should +not be called by the caller of `pthread_join()`. === Region and Data Messages These are concerned with recording performance data -over regions or spans of code. e.g: -`void trace2_region_enter(const char *category, const char *label, const struct repository *repo)`. +over regions or spans of code. + +`void trace2_region_enter(const char *category, const char *label, const struct repository *repo)`:: + +`void trace2_region_enter_printf(const char *category, const char *label, const struct repository *repo, const char *fmt, ...)`:: + +`void trace2_region_enter_printf_va(const char *category, const char *label, const struct repository *repo, const char *fmt, va_list ap)`:: + + Emits a thread-relative "region_enter" message with optional + printf string. ++ +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_leave(const char *category, const char *label, const struct repository *repo)`:: + +`void trace2_region_leave_printf(const char *category, const char *label, const struct repository *repo, const char *fmt, ...)`:: + +`void trace2_region_leave_printf_va(const char *category, const char *label, const struct repository *repo, const char *fmt, va_list ap)`:: + + Emits a thread-relative "region_leave" message with optional + printf string. ++ +This function pops the region nesting stack on the current thread +and reports the elapsed time of the stack frame. ++ +The `category`, `label`, and `repo` fields are the same as above. +The `category` and `label` do not need to match the correpsonding +"region_enter" message, but it makes the data stream easier to +understand. + +`void trace2_data_string(const char *category, const struct repository *repo, const char *key, const char * value)`:: + +`void trace2_data_intmax(const char *category, const struct repository *repo, const char *key, intmax value)`:: + +`void trace2_data_json(const char *category, const struct repository *repo, const char *key, const struct json_writer *jw)`:: -Refer to trace2.h for details about all trace2 functions. + Emits a region- and thread-relative "data" or "data_json" message. ++ +This is a key/value pair message containing information about the +current thread, region stack, and repository. This could be used +to print the number of files in a directory during a multi-threaded +recursive tree walk. + +`void trace2_printf(const char *fmt, ...)`:: + +`void trace2_printf_va(const char *fmt, va_list ap)`:: + + Emits a region- and thread-relative "printf" message. == Trace2 Target Formats @@ -379,35 +605,17 @@ only present on the "start" and "atexit" events. ==== Event-Specific Key/Value Pairs `"version"`:: - This event gives the version of the executable and the EVENT format. It - should always be the first event in a trace session. The EVENT format - version will be incremented if new event types are added, if existing - fields are removed, or if there are significant changes in - interpretation of existing events or fields. Smaller changes, such as - adding a new field to an existing event, will not require an increment - to the EVENT format version. + This event gives the version of the executable and the EVENT format. + ------------ { "event":"version", ... - "evt":"2", # EVENT format version + "evt":"1", # EVENT format version "exe":"2.20.1.155.g426c96fcdb" # git version } ------------ -`"discard"`:: - This event is written to the git-trace2-discard sentinel file if there - are too many files in the target trace directory (see the - trace2.maxFiles config option). -+ ------------- -{ - "event":"discard", - ... -} ------------- - `"start"`:: This event contains the complete argv received by main(). + @@ -591,7 +799,7 @@ with "?". Note that the session-id of the child process is not available to the current/spawning process, so the child's PID is reported here as a hint for post-processing. (But it is only a hint because the child -process may be a shell script which doesn't have a session-id.) +proces may be a shell script which doesn't have a session-id.) + Note that the `t_rel` field contains the observed run time in seconds for the child process (starting before the fork/exec/spawn and @@ -951,7 +1159,7 @@ d0 | main | atexit | | 0.028809 | | + Regions may be nested. This causes messages to be indented in the PERF target, for example. -Elapsed times are relative to the start of the corresponding nesting +Elapsed times are relative to the start of the correpsonding nesting level as expected. For example, if we add region message to: + ---------------- @@ -1146,7 +1354,7 @@ d0 | main | atexit | | 0.030027 | | In this example, the preload region took 0.009122 seconds. The 7 threads took between 0.006069 and 0.008947 seconds to work on their portion of the index. Thread "th01" worked on 508 items at offset 0. Thread "th02" -worked on 508 items at offset 2032. Thread "th04" worked on 508 items +worked on 508 items at offset 2032. Thread "th04" worked on 508 itemts at offset 508. + This example also shows that thread names are assigned in a racy manner |