[PATCH 1 of 3 v2] profiling: allow nested usage of maybeprofile

[Yuya Nishihara]

On Mon, 19 Sep 2016 16:13:56 -0700, Arun Kulshreshtha wrote:
> # HG changeset patch
> # User Arun Kulshreshtha <kulshrax at fb.com>
> # Date 1474324901 25200
> #      Mon Sep 19 15:41:41 2016 -0700
> # Node ID 679c90104cc1fc92099ede6bd359f6ab5b10640d
> # Parent  285a8c3e53f2183438f0cdbc238e4ab851d0d110
> profiling: allow nested usage of maybeprofile
> 
> Add a check to the maybeprofile context manager to ensure that profiling
> is only enabled once in nested invocations of this context manager.
> 
> Updated in v2 of this patch to reset itself once the root invocation
> has exited. While not currently used, this ensures that maybeprofile
> can be used in multiple (non-nested) places in a single run.
> 
> diff --git a/mercurial/profiling.py b/mercurial/profiling.py
> --- a/mercurial/profiling.py
> +++ b/mercurial/profiling.py
> @@ -157,8 +157,15 @@
>      just use a single code path for calling into code you may want to profile
>      and this function determines whether to start profiling.
>      """
> -    if ui.configbool('profiling', 'enabled'):
> +
> +    # Guard against nested invocations of this context manager.
> +    # Profiling should only be started in the outermost invocation.
> +    alreadyenabled = getattr(maybeprofile, 'enabled', False)
> +
> +    if ui.configbool('profiling', 'enabled') and not alreadyenabled:
> +        maybeprofile.enabled = True
>          with profile(ui):
>              yield
> +        maybeprofile.enabled = False

maybeprofile() can be called in threads. If we need to prevent nesting, we'll
have to save the flag in TLS.

Also, I think that should be managed by profile() or (ls|flame|stat)profile().