/3rd_party/llvm/include/llvm/Support/Mutex.h

  1//===- llvm/Support/Mutex.h - Mutex Operating System Concept -----*- C++ -*-===//
  2//
  3//                     The LLVM Compiler Infrastructure
  4//
  5// This file is distributed under the University of Illinois Open Source
  6// License. See LICENSE.TXT for details.
  7//
  8//===----------------------------------------------------------------------===//
  9//
 10// This file declares the llvm::sys::Mutex class.
 11//
 12//===----------------------------------------------------------------------===//
 13
 14#ifndef LLVM_SUPPORT_MUTEX_H
 15#define LLVM_SUPPORT_MUTEX_H
 16
 17#include "llvm/Support/Compiler.h"
 18#include "llvm/Support/Threading.h"
 19#include <cassert>
 20
 21namespace llvm
 22{
 23  namespace sys
 24  {
 25    /// @brief Platform agnostic Mutex class.
 26    class MutexImpl
 27    {
 28    /// @name Constructors
 29    /// @{
 30    public:
 31
 32      /// Initializes the lock but doesn't acquire it. if \p recursive is set
 33      /// to false, the lock will not be recursive which makes it cheaper but
 34      /// also more likely to deadlock (same thread can't acquire more than
 35      /// once).
 36      /// @brief Default Constructor.
 37      explicit MutexImpl(bool recursive = true);
 38
 39      /// Releases and removes the lock
 40      /// @brief Destructor
 41      ~MutexImpl();
 42
 43    /// @}
 44    /// @name Methods
 45    /// @{
 46    public:
 47
 48      /// Attempts to unconditionally acquire the lock. If the lock is held by
 49      /// another thread, this method will wait until it can acquire the lock.
 50      /// @returns false if any kind of error occurs, true otherwise.
 51      /// @brief Unconditionally acquire the lock.
 52      bool acquire();
 53
 54      /// Attempts to release the lock. If the lock is held by the current
 55      /// thread, the lock is released allowing other threads to acquire the
 56      /// lock.
 57      /// @returns false if any kind of error occurs, true otherwise.
 58      /// @brief Unconditionally release the lock.
 59      bool release();
 60
 61      /// Attempts to acquire the lock without blocking. If the lock is not
 62      /// available, this function returns false quickly (without blocking). If
 63      /// the lock is available, it is acquired.
 64      /// @returns false if any kind of error occurs or the lock is not
 65      /// available, true otherwise.
 66      /// @brief Try to acquire the lock.
 67      bool tryacquire();
 68
 69    //@}
 70    /// @name Platform Dependent Data
 71    /// @{
 72    private:
 73      void* data_; ///< We don't know what the data will be
 74
 75    /// @}
 76    /// @name Do Not Implement
 77    /// @{
 78    private:
 79      MutexImpl(const MutexImpl &) LLVM_DELETED_FUNCTION;
 80      void operator=(const MutexImpl &) LLVM_DELETED_FUNCTION;
 81    /// @}
 82    };
 83
 84
 85    /// SmartMutex - A mutex with a compile time constant parameter that
 86    /// indicates whether this mutex should become a no-op when we're not
 87    /// running in multithreaded mode.
 88    template<bool mt_only>
 89    class SmartMutex : public MutexImpl {
 90      unsigned acquired;
 91      bool recursive;
 92    public:
 93      explicit SmartMutex(bool rec = true) :
 94        MutexImpl(rec), acquired(0), recursive(rec) { }
 95
 96      bool acquire() {
 97        if (!mt_only || llvm_is_multithreaded()) {
 98          return MutexImpl::acquire();
 99        } else {
100          // Single-threaded debugging code.  This would be racy in
101          // multithreaded mode, but provides not sanity checks in single
102          // threaded mode.
103          assert((recursive || acquired == 0) && "Lock already acquired!!");
104          ++acquired;
105          return true;
106        }
107      }
108
109      bool release() {
110        if (!mt_only || llvm_is_multithreaded()) {
111          return MutexImpl::release();
112        } else {
113          // Single-threaded debugging code.  This would be racy in
114          // multithreaded mode, but provides not sanity checks in single
115          // threaded mode.
116          assert(((recursive && acquired) || (acquired == 1)) &&
117                 "Lock not acquired before release!");
118          --acquired;
119          return true;
120        }
121      }
122
123      bool tryacquire() {
124        if (!mt_only || llvm_is_multithreaded())
125          return MutexImpl::tryacquire();
126        else return true;
127      }
128
129      private:
130        SmartMutex(const SmartMutex<mt_only> & original);
131        void operator=(const SmartMutex<mt_only> &);
132    };
133
134    /// Mutex - A standard, always enforced mutex.
135    typedef SmartMutex<false> Mutex;
136
137    template<bool mt_only>
138    class SmartScopedLock  {
139      SmartMutex<mt_only>& mtx;
140
141    public:
142      SmartScopedLock(SmartMutex<mt_only>& m) : mtx(m) {
143        mtx.acquire();
144      }
145
146      ~SmartScopedLock() {
147        mtx.release();
148      }
149    };
150
151    typedef SmartScopedLock<false> ScopedLock;
152  }
153}
154
155#endif