From: Jeff Hostetler <jeffh...@microsoft.com>
Teach git to create a unique session id (SID) during structured
logging initialization and use that SID in all log events.
This SID is exported into a transient environment variable and
inherited by child processes. This allows git child processes
to be related back to the parent git process event if there are
intermediate /bin/sh processes between them.
Update t0001 to ignore the environment variable GIT_SLOG_PARENT_SID.
Signed-off-by: Jeff Hostetler <jeffh...@microsoft.com>
---
Documentation/git.txt | 6 ++++++
structured-logging.c | 52 +++++++++++++++++++++++++++++++++++++++++++++++++++
t/t0001-init.sh | 1 +
3 files changed, 59 insertions(+)
diff --git a/Documentation/git.txt b/Documentation/git.txt
index dba7f0c..a24f399 100644
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -766,6 +766,12 @@ standard output.
adequate and support for it is likely to be removed in the
foreseeable future (along with the variable).
+`GIT_SLOG_PARENT_SID`::
+ (Experimental) A transient environment variable set by top-level
+ Git commands and inherited by child Git commands. It contains
+ a session id that will be written the structured logging output
+ to help associate child and parent processes.
+
Discussion[[Discussion]]
------------------------
diff --git a/structured-logging.c b/structured-logging.c
index afa2224..289140f 100644
--- a/structured-logging.c
+++ b/structured-logging.c
@@ -31,9 +31,57 @@ static char *my__command_name;
static char *my__sub_command_name;
static struct argv_array my__argv = ARGV_ARRAY_INIT;
+static struct strbuf my__session_id = STRBUF_INIT;
static struct json_writer my__errors = JSON_WRITER_INIT;
/*
+ * Compute a new session id for the current process. Build string
+ * with the start time and PID of the current process and append
+ * the inherited session id from our parent process (if present).
+ * The parent session id may include its parent session id.
+ *
+ * sid := <start-time> '-' <pid> [ ':' <parent-sid> [ ... ] ]
+ */
+static void compute_our_sid(void)
+{
+ const char *parent_sid;
+
+ if (my__session_id.len)
+ return;
+
+ /*
+ * A "session id" (SID) is a cheap, unique-enough string to
+ * associate child process with the hierarchy of invoking git
+ * processes.
+ *
+ * This is stronger than a simple parent-pid because we may
+ * have an intermediate shell between a top-level Git command
+ * and a child Git command. It also isolates from issues
+ * about how the OS recycles PIDs.
+ *
+ * This could be a UUID/GUID, but that is overkill for our
+ * needs here and more expensive to compute.
+ *
+ * Consumers should consider this an unordered opaque string
+ * in case we decide to switch to a real UUID in the future.
+ */
+ strbuf_addf(&my__session_id, "%"PRIuMAX"-%"PRIdMAX,
+ (uintmax_t)my__start_time, (intmax_t)my__pid);
+
+ parent_sid = getenv("GIT_SLOG_PARENT_SID");
+ if (parent_sid && *parent_sid) {
+ strbuf_addch(&my__session_id, ':');
+ strbuf_addstr(&my__session_id, parent_sid);
+ }
+
+ /*
+ * Install our SID into the environment for our child processes
+ * to inherit.
+ */
+ setenv("GIT_SLOG_PARENT_SID", my__session_id.buf, 1);
+}
+
+/*
* Write a single event to the structured log file.
*/
static void emit_event(struct json_writer *jw, const char *event_name)
@@ -75,6 +123,7 @@ static void emit_start_event(void)
jw_object_string(&jw, "event", "cmd_start");
jw_object_intmax(&jw, "clock_us", (intmax_t)my__start_time);
jw_object_intmax(&jw, "pid", (intmax_t)my__pid);
+ jw_object_string(&jw, "sid", my__session_id.buf);
if (my__command_name && *my__command_name)
jw_object_string(&jw, "command", my__command_name);
@@ -112,6 +161,7 @@ static void emit_exit_event(void)
jw_object_string(&jw, "event", "cmd_exit");
jw_object_intmax(&jw, "clock_us", (intmax_t)atexit_time);
jw_object_intmax(&jw, "pid", (intmax_t)my__pid);
+ jw_object_string(&jw, "sid", my__session_id.buf);
if (my__command_name && *my__command_name)
jw_object_string(&jw, "command", my__command_name);
@@ -250,6 +300,7 @@ static void do_final_steps(int in_signal)
free(my__sub_command_name);
argv_array_clear(&my__argv);
jw_release(&my__errors);
+ strbuf_release(&my__session_id);
}
static void slog_atexit(void)
@@ -289,6 +340,7 @@ static void initialize(int argc, const char **argv)
{
my__start_time = getnanotime() / 1000;
my__pid = getpid();
+ compute_our_sid();
intern_argv(argc, argv);
diff --git a/t/t0001-init.sh b/t/t0001-init.sh
index c413bff..3dfc37a 100755
--- a/t/t0001-init.sh
+++ b/t/t0001-init.sh
@@ -92,6 +92,7 @@ test_expect_success 'No extra GIT_* on alias scripts' '
env |
sed -n \
-e "/^GIT_PREFIX=/d" \
+ -e "/^GIT_SLOG_PARENT_SID=/d" \
-e "/^GIT_TEXTDOMAINDIR=/d" \
-e "/^GIT_/s/=.*//p" |
sort
--
2.9.3
