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#if defined(LLVM_ENABLE_THREADS) && LLVM_ENABLE_THREADS != 0
74      void* data_; ///< We don't know what the data will be
75#endif
76
77    /// @}
78    /// @name Do Not Implement
79    /// @{
80    private:
81      MutexImpl(const MutexImpl &) = delete;
82      void operator=(const MutexImpl &) = delete;
83    /// @}
84    };
85
86
87    /// SmartMutex - A mutex with a compile time constant parameter that
88    /// indicates whether this mutex should become a no-op when we're not
89    /// running in multithreaded mode.
90    template<bool mt_only>
91    class SmartMutex {
92      MutexImpl impl;
93      unsigned acquired;
94      bool recursive;
95    public:
96      explicit SmartMutex(bool rec = true) :
97        impl(rec), acquired(0), recursive(rec) { }
98
99      bool lock() {
100        if (!mt_only || llvm_is_multithreaded()) {
101          return impl.acquire();
102        } else {
103          // Single-threaded debugging code.  This would be racy in
104          // multithreaded mode, but provides not sanity checks in single
105          // threaded mode.
106          assert((recursive || acquired == 0) && "Lock already acquired!!");
107          ++acquired;
108          return true;
109        }
110      }
111
112      bool unlock() {
113        if (!mt_only || llvm_is_multithreaded()) {
114          return impl.release();
115        } else {
116          // Single-threaded debugging code.  This would be racy in
117          // multithreaded mode, but provides not sanity checks in single
118          // threaded mode.
119          assert(((recursive && acquired) || (acquired == 1)) &&
120                 "Lock not acquired before release!");
121          --acquired;
122          return true;
123        }
124      }
125
126      bool try_lock() {
127        if (!mt_only || llvm_is_multithreaded())
128          return impl.tryacquire();
129        else return true;
130      }
131
132      private:
133        SmartMutex(const SmartMutex<mt_only> & original);
134        void operator=(const SmartMutex<mt_only> &);
135    };
136
137    /// Mutex - A standard, always enforced mutex.
138    typedef SmartMutex<false> Mutex;
139
140    template<bool mt_only>
141    class SmartScopedLock  {
142      SmartMutex<mt_only>& mtx;
143
144    public:
145      SmartScopedLock(SmartMutex<mt_only>& m) : mtx(m) {
146        mtx.lock();
147      }
148
149      ~SmartScopedLock() {
150        mtx.unlock();
151      }
152    };
153
154    typedef SmartScopedLock<false> ScopedLock;
155  }
156}
157
158#endif
159