Create a test-tool helper to create the server side of
a windows named pipe, wait for a client connection, and
copy data written to the pipe to stdout.

Create t0051 test to route GIT_TRACE output of a command
to a named pipe using the above test-tool helper.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>

Create a new unified tracing facility for git.  The eventual intent is to
replace the current trace_printf* and trace_performance* routines with a
unified set of git_trace2* routines.

In addition to the usual printf-style API, trace2 provides higer-level
event verbs with fixed-fields allowing structured data to be written.
This makes post-processing and analysis easier for external tools.

Trace2 defines 3 output targets.  These are set using the environment
variables "GIT_TR2", "GIT_TR2_PERF", and "GIT_TR2_EVENT".  These may be
set to "1" or to an absolute pathname (just like the current GIT_TRACE).

* GIT_TR2 is intended to be a replacement for GIT_TRACE and logs command
  summary data.

* GIT_TR2_PERF is intended as a replacement for GIT_TRACE_PERFORMANCE.
  It extends the output with columns for the command process, thread,
  repo, absolute and relative elapsed times.  It reports events for
  child process start/stop, thread start/stop, and per-thread function
  nesting.

* GIT_TR2_EVENT is a new structured format. It writes event data as a
  series of JSON records.

Calls to trace2 functions log to any of the 3 output targets enabled
without the need to call different trace_printf* or trace_performance*
routines.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>

Add trace2_region_enter() and trace2_region_leave() calls around the
various phases of a status scan.  This gives elapsed time for each
phase in the GIT_TR2_PERF and GIT_TR2_EVENT trace target.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>

Classify editor, pager, and sub-process child processes.

The former two can be used to identify interactive commands,
for example.  A later effort could classify other types of
commands, such as "gc", "hook", and etc.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>

Add trace2 events when reading and writing the index.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>

Add trace2 region and data events describing attempts to deserialize
status data using a status cache.

A category:status, label:deserialize region is pushed around the
deserialize code.

Deserialization results when reading from a file are:
    category:status, path   = <path>
    category:status, polled = <number_of_attempts>
    category:status, result = "ok" | "reject"

When reading from STDIN are:
    category:status, path   = "STDIN"
    category:status, result = "ok" | "reject"

Status will fallback and run a normal status scan when a "reject"
is reported (unless "--deserialize-wait=fail").  If "ok" is reported,
status was able to use the status cache and avoid scanning the workdir.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>