From: Christopher Dykes <cdykes@fb.com>
Date: Mon, 17 Apr 2017 22:40:29 +0000 (-0700)
Subject: Don't invoke undefined behavior when getting the pthread_t out of std::thread::id
X-Git-Tag: v2017.04.24.00~15
X-Git-Url: http://plrg.eecs.uci.edu/git/?a=commitdiff_plain;h=43c0c2c5bf5288e64e15edba105d864986c76add;p=folly.git

Don't invoke undefined behavior when getting the pthread_t out of std::thread::id

Summary: This assumes I understand strict-aliasing rules correctly.

Reviewed By: yfeldblum

Differential Revision: D4900118

fbshipit-source-id: edba535d3ba799ac665d3f859dc4154b2c1b22cb
---

diff --git a/folly/ThreadName.h b/folly/ThreadName.h
index ad773033..0a292a53 100644
--- a/folly/ThreadName.h
+++ b/folly/ThreadName.h
@@ -85,7 +85,8 @@ inline bool setThreadName(std::thread::id id, StringPiece name) {
   // In most implementations, std::thread::id is a thin wrapper around
   // std::thread::native_handle_type, which means we can do unsafe things to
   // extract it.
-  pthread_t ptid = *reinterpret_cast<pthread_t*>(&id);
+  pthread_t ptid;
+  std::memcpy(&ptid, &id, sizeof(pthread_t));
   return setThreadName(ptid, name);
 }