trace2: refactor setting process starting time

Create trace2_initialize_clock() and call from main() to capture
process start time in isolation and before other sub-systems are
ready.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 17 insertions, 0 deletions

diff --git a/trace2.h b/trace2.h
index ae5020d0e6..8f89e70c44 100644
--- a/trace2.h
+++ b/trace2.h
@@ -20,6 +20,23 @@ struct json_writer;
  */
 
 /*
+ * Initialize the TRACE2 clock and do nothing else, in particular
+ * no mallocs, no system inspection, and no environment inspection.
+ *
+ * This should be called at the very top of main() to capture the
+ * process start time.  This is intended to reduce chicken-n-egg
+ * bootstrap pressure.
+ *
+ * It is safe to call this more than once.  This allows capturing
+ * absolute startup costs on Windows which uses a little trickery
+ * to do setup work before common-main.c:main() is called.
+ *
+ * The main trace2_initialize_fl() may be called a little later
+ * after more infrastructure is established.
+ */
+void trace2_initialize_clock(void);
+
+/*
  * Initialize TRACE2 tracing facility if any of the builtin TRACE2
  * targets are enabled in the environment.  Emits a 'version' event.
  *