From 15cd8be93e617f0ebee4e21ffa659193d8eff5bc Mon Sep 17 00:00:00 2001
From: Michael Hitchens <hitchens@google.com>
Date: Mon, 2 May 2022 21:49:25 +0000
Subject: [PATCH] style: Update guidance on #include <mutex>

Can `#include <mutex>` in order to use `std::lock_guard`. However, the
other types in this header aren't guaranteed to work for a given
toolchain or OS. For types like std::mutex, pw_sync alternatives should
be preferred.

Bug: b/230744747
Change-Id: I782b02175e21a7729efd255a797ee8549541b03f
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/93221
Reviewed-by: Keir Mierle <keir@google.com>
Reviewed-by: Wyatt Hepler <hepler@google.com>
Commit-Queue: Keir Mierle <keir@google.com>
---
 docs/style_guide.rst | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/docs/style_guide.rst b/docs/style_guide.rst
index 0cb1aa9ac4..19a9996933 100644
--- a/docs/style_guide.rst
+++ b/docs/style_guide.rst
@@ -128,6 +128,7 @@ Permitted Headers
    * ``<atomic>`` -- not all MCUs natively support atomic operations
    * ``<bitset>`` -- conversions to or from strings are disallowed
    * ``<functional>`` -- do **not** use ``std::function``
+   * ``<mutex>`` -- can use ``std::lock_guard``, prefer :ref:`module-pw_sync`
    * ``<new>`` -- for placement new
    * ``<numeric>`` -- be wary of code size with multiple template instantiations
 
@@ -137,7 +138,7 @@ Permitted Headers
    * Dynamic containers (``<list>``, ``<map>``, ``<set>``, ``<vector>``, etc.)
    * Streams (``<iostream>``, ``<ostream>``, ``<fstream>``, etc.)
    * ``<exception>``
-   * ``<future>``, ``<mutex>``, ``<thread>``
+   * ``<future>``, ``<thread>``
    * ``<memory>``
    * ``<regex>``
    * ``<scoped_allocator>``