LLVM  3.7.0
Mutex.h
Go to the documentation of this file.
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 
21 namespace 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.
139 
140  template<bool mt_only>
142  SmartMutex<mt_only>& mtx;
143 
144  public:
146  mtx.lock();
147  }
148 
150  mtx.unlock();
151  }
152  };
153 
155  }
156 }
157 
158 #endif
bool acquire()
Attempts to unconditionally acquire the lock.
Definition: Mutex.cpp:84
SmartMutex - A mutex with a compile time constant parameter that indicates whether this mutex should ...
Definition: Mutex.h:91
SmartMutex(bool rec=true)
Definition: Mutex.h:96
bool release()
Attempts to release the lock.
Definition: Mutex.cpp:94
SmartMutex< false > Mutex
Mutex - A standard, always enforced mutex.
Definition: Mutex.h:138
MutexImpl(bool recursive=true)
Initializes the lock but doesn't acquire it.
Definition: Mutex.cpp:44
bool llvm_is_multithreaded()
Returns true if LLVM is compiled with support for multi-threading, and false otherwise.
Definition: Threading.cpp:23
SmartScopedLock< false > ScopedLock
Definition: Mutex.h:154
Platform agnostic Mutex class.
Definition: Mutex.h:26
SmartScopedLock(SmartMutex< mt_only > &m)
Definition: Mutex.h:145
~MutexImpl()
Releases and removes the lock.
Definition: Mutex.cpp:75
bool tryacquire()
Attempts to acquire the lock without blocking.
Definition: Mutex.cpp:104