[RFC PATCH v1 0/3] Fix undefined behavior in the C++ mutex implementation

[Alviro Iskandar Setiawan <alviro.iskandar@gnuweeb.org>]

Hi,

The current C++ mutex implementation is undefined behavior, specifically
in the cond_wait() function because std::unique_lock<std::mutex> is
constructed with std::defer_lock while the same thread has acquired the
lock. Also, right after that defer_lock, std::condition_variable calls
wait() with a unique lock, not in a locked state.

In such a situation, the correct construction is using std::adopt_lock.
However, using std::adopt_lock leads to another issue. The issue is the
lock will be released upon return in the cond_wait(). To solve the
problem, introduce a new helper function, __cond_wait() which will
release the lock with std::adopt_lock and then call it from cond_wait().
The cond_wait() then acquires the lock again before it returns. The
result is that we correctly fulfill the __must_hold() semantic while
conforming to the C++ mutex implementation.

Signed-off-by: Alviro Iskandar Setiawan <alviro.iskandar@gnuweeb.org>
---
Alviro Iskandar Setiawan (3):
  MAINTAINERS: Add myself as the thread maintainer
  core/thread: Fix undefined behavior in the C++ mutex implementation
  configure: Introduce `--cpp-thread` option

 MAINTAINERS         |  7 +++++++
 configure           |  8 ++++++++
 core/thread.cc      | 17 +++++++++++++----
 include/gw/thread.h |  2 +-
 4 files changed, 29 insertions(+), 5 deletions(-)


base-commit: 2ca56f61c307813ad7069cf08c350f2ff61fc615
-- 
Alviro Iskandar Setiawan