Mutex.h revision 218885 
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_SYSTEM_MUTEX_H
15#define LLVM_SYSTEM_MUTEX_H
16
17#include "llvm/Support/Threading.h"
18#include <cassert>
19
20namespace llvm
21{
22  namespace sys
23  {
24    /// @brief Platform agnostic Mutex class.
25    class MutexImpl
26    {
27    /// @name Constructors
28    /// @{
29    public:
30
31      /// Initializes the lock but doesn't acquire it. if \p recursive is set
32      /// to false, the lock will not be recursive which makes it cheaper but
33      /// also more likely to deadlock (same thread can't acquire more than
34      /// once).
35      /// @brief Default Constructor.
36      explicit MutexImpl(bool recursive = true);
37
38      /// Releases and removes the lock
39      /// @brief Destructor
40      ~MutexImpl();
41
42    /// @}
43    /// @name Methods
44    /// @{
45    public:
46
47      /// Attempts to unconditionally acquire the lock. If the lock is held by
48      /// another thread, this method will wait until it can acquire the lock.
49      /// @returns false if any kind of error occurs, true otherwise.
50      /// @brief Unconditionally acquire the lock.
51      bool acquire();
52
53      /// Attempts to release the lock. If the lock is held by the current
54      /// thread, the lock is released allowing other threads to acquire the
55      /// lock.
56      /// @returns false if any kind of error occurs, true otherwise.
57      /// @brief Unconditionally release the lock.
58      bool release();
59
60      /// Attempts to acquire the lock without blocking. If the lock is not
61      /// available, this function returns false quickly (without blocking). If
62      /// the lock is available, it is acquired.
63      /// @returns false if any kind of error occurs or the lock is not
64      /// available, true otherwise.
65      /// @brief Try to acquire the lock.
66      bool tryacquire();
67
68    //@}
69    /// @name Platform Dependent Data
70    /// @{
71    private:
72      void* data_; ///< We don't know what the data will be
73
74    /// @}
75    /// @name Do Not Implement
76    /// @{
77    private:
78      MutexImpl(const MutexImpl & original);
79      void operator=(const MutexImpl &);
80    /// @}
81    };
82
83
84    /// SmartMutex - A mutex with a compile time constant parameter that
85    /// indicates whether this mutex should become a no-op when we're not
86    /// running in multithreaded mode.
87    template<bool mt_only>
88    class SmartMutex : public MutexImpl {
89      unsigned acquired;
90      bool recursive;
91    public:
92      explicit SmartMutex(bool rec = true) :
93        MutexImpl(rec), acquired(0), recursive(rec) { }
94
95      bool acquire() {
96        if (!mt_only || llvm_is_multithreaded()) {
97          return MutexImpl::acquire();
98        } else {
99          // Single-threaded debugging code.  This would be racy in
100          // multithreaded mode, but provides not sanity checks in single
101          // threaded mode.
102          assert((recursive || acquired == 0) && "Lock already acquired!!");
103          ++acquired;
104          return true;
105        }
106      }
107
108      bool release() {
109        if (!mt_only || llvm_is_multithreaded()) {
110          return MutexImpl::release();
111        } else {
112          // Single-threaded debugging code.  This would be racy in
113          // multithreaded mode, but provides not sanity checks in single
114          // threaded mode.
115          assert(((recursive && acquired) || (acquired == 1)) &&
116                 "Lock not acquired before release!");
117          --acquired;
118          return true;
119        }
120      }
121
122      bool tryacquire() {
123        if (!mt_only || llvm_is_multithreaded())
124          return MutexImpl::tryacquire();
125        else return true;
126      }
127
128      private:
129        SmartMutex(const SmartMutex<mt_only> & original);
130        void operator=(const SmartMutex<mt_only> &);
131    };
132
133    /// Mutex - A standard, always enforced mutex.
134    typedef SmartMutex<false> Mutex;
135
136    template<bool mt_only>
137    class SmartScopedLock  {
138      SmartMutex<mt_only>& mtx;
139
140    public:
141      SmartScopedLock(SmartMutex<mt_only>& m) : mtx(m) {
142        mtx.acquire();
143      }
144
145      ~SmartScopedLock() {
146        mtx.release();
147      }
148    };
149
150    typedef SmartScopedLock<false> ScopedLock;
151  }
152}
153
154#endif
155