Mutex.h revision a9d1f2c559ef4b2549e29288fe6944e68913ba0f 
1//===- llvm/System/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/System/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
99        // Single-threaded debugging code.  This would be racy in multithreaded
100        // mode, but provides not sanity checks in single threaded mode.
101        assert((recursive || acquired == 0) && "Lock already acquired!!");
102        ++acquired;
103        return true;
104      }
105
106      bool release() {
107        if (!mt_only || llvm_is_multithreaded())
108          return MutexImpl::release();
109
110        // Single-threaded debugging code.  This would be racy in multithreaded
111        // mode, but provides not sanity checks in single threaded mode.
112        assert(((recursive && acquired) || (acquired == 1)) &&
113               "Lock not acquired before release!");
114        --acquired;
115        return true;
116      }
117
118      bool tryacquire() {
119        if (!mt_only || llvm_is_multithreaded())
120          return MutexImpl::tryacquire();
121        return true;
122      }
123
124      private:
125        SmartMutex(const SmartMutex<mt_only> & original);
126        void operator=(const SmartMutex<mt_only> &);
127    };
128
129    /// Mutex - A standard, always enforced mutex.
130    typedef SmartMutex<false> Mutex;
131
132    template<bool mt_only>
133    class SmartScopedLock  {
134      SmartMutex<mt_only>& mtx;
135
136    public:
137      SmartScopedLock(SmartMutex<mt_only>& m) : mtx(m) {
138        mtx.acquire();
139      }
140
141      ~SmartScopedLock() {
142        mtx.release();
143      }
144    };
145
146    typedef SmartScopedLock<false> ScopedLock;
147  }
148}
149
150#endif
151