[flang-commits] [PATCH] D126291: [flang][Driver] Update link job on windows

[Markus Mützel via Phabricator via flang-commits]

mmuetzel added a comment.

In D126291#3556725 <https://reviews.llvm.org/D126291#3556725>, @mstorsjo wrote:

> This looks mostly reasonable, but I'd recommend using a windows critical section instead of a mutex - a critical section doesn't invoke the kernel when there's no contention of the lock. For that, you'd use `CRITICAL_SECTION`, `InitializeCriticalSection(&cs);`, `EnterCriticalSection(&cs);`, `LeaveCriticalSection(&cs);`, `DeleteCriticalSection(&cs);`.

Thanks for the feedback.
Updated patch:

  From 511c2f7695fe667486b5c07fb024f4badec6b23a Mon Sep 17 00:00:00 2001
  From: =?UTF-8?q?Markus=20M=C3=BCtzel?= <markus.muetzel at gmx.de>
  Date: Fri, 3 Jun 2022 21:59:02 +0200
  Subject: [PATCH] lock without <mutex> on Windows
  
  ---
   flang/runtime/lock.h | 24 ++++++++++--------------
   1 file changed, 10 insertions(+), 14 deletions(-)
  
  diff --git a/flang/runtime/lock.h b/flang/runtime/lock.h
  index 0abc1158c2c1..c3572c72d17d 100644
  --- a/flang/runtime/lock.h
  +++ b/flang/runtime/lock.h
  @@ -15,23 +15,17 @@
   
   // Avoid <mutex> if possible to avoid introduction of C++ runtime
   // library dependence.
  -#ifndef _WIN32
  -#define USE_PTHREADS 1
  +#ifdef _WIN32
  +#include <windows.h>
   #else
  -#undef USE_PTHREADS
  -#endif
  -
  -#if USE_PTHREADS
   #include <pthread.h>
  -#else
  -#include <mutex>
   #endif
   
   namespace Fortran::runtime {
   
   class Lock {
   public:
  -#if USE_PTHREADS
  +#ifndef _WIN32
     Lock() { pthread_mutex_init(&mutex_, nullptr); }
     ~Lock() { pthread_mutex_destroy(&mutex_); }
     void Take() {
  @@ -41,9 +35,11 @@ public:
     bool Try() { return pthread_mutex_trylock(&mutex_) == 0; }
     void Drop() { pthread_mutex_unlock(&mutex_); }
   #else
  -  void Take() { mutex_.lock(); }
  -  bool Try() { return mutex_.try_lock(); }
  -  void Drop() { mutex_.unlock(); }
  +  Lock() { InitializeCriticalSection(&cs_); }
  +  ~Lock() { DeleteCriticalSection(&cs_); }
  +  void Take() { EnterCriticalSection(&cs_); }
  +  bool Try() { return TryEnterCriticalSection(&cs_); }
  +  void Drop() { LeaveCriticalSection(&cs_); }
   #endif
   
     void CheckLocked(const Terminator &terminator) {
  @@ -54,10 +50,10 @@ public:
     }
   
   private:
  -#if USE_PTHREADS
  +#ifndef _WIN32
     pthread_mutex_t mutex_{};
   #else
  -  std::mutex mutex_;
  +  CRITICAL_SECTION cs_;
   #endif
   };
   
  -- 
  2.35.3.windows.1

Also works for me with the simple Hello World on MinGW (MSYS2 CLANG64).


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