include/llvm/Support/Mutex.h

   1 //===- llvm/Support/Mutex.h - Mutex Operating System Concept -----*- C++ -*-===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8 //
   9 // This file declares the llvm::sys::Mutex class.
  10 //
  11 //===----------------------------------------------------------------------===//
  12
  13 #ifndef LLVM_SUPPORT_MUTEX_H
  14 #define LLVM_SUPPORT_MUTEX_H
  15
  16 #include "llvm/Support/Threading.h"
  17 #include <cassert>
  18 #include <mutex>
  19
  20 namespace llvm
  21 {
  22   namespace sys
  23   {
  24     /// SmartMutex - A mutex with a compile time constant parameter that
  25     /// indicates whether this mutex should become a no-op when we're not
  26     /// running in multithreaded mode.
  27     template<bool mt_only>
  28     class SmartMutex {
  29       std::recursive_mutex impl;
  30       unsigned acquired = 0;
  31
  32     public:
  33       bool lock() {
  34         if (!mt_only || llvm_is_multithreaded()) {
  35           impl.lock();
  36           return true;
  37         } else {
  38           // Single-threaded debugging code.  This would be racy in
  39           // multithreaded mode, but provides not sanity checks in single
  40           // threaded mode.
  41           ++acquired;
  42           return true;
  43         }
  44       }
  45
  46       bool unlock() {
  47         if (!mt_only || llvm_is_multithreaded()) {
  48           impl.unlock();
  49           return true;
  50         } else {
  51           // Single-threaded debugging code.  This would be racy in
  52           // multithreaded mode, but provides not sanity checks in single
  53           // threaded mode.
  54           assert(acquired && "Lock not acquired before release!");
  55           --acquired;
  56           return true;
  57         }
  58       }
  59
  60       bool try_lock() {
  61         if (!mt_only || llvm_is_multithreaded())
  62           return impl.try_lock();
  63         else return true;
  64       }
  65     };
  66
  67     /// Mutex - A standard, always enforced mutex.
  68     typedef SmartMutex<false> Mutex;
  69
  70     template <bool mt_only>
  71     using SmartScopedLock = std::lock_guard<SmartMutex<mt_only>>;
  72
  73     typedef SmartScopedLock<false> ScopedLock;
  74   }
  75 }
  76
  77 #endif