LLVM  9.0.0svn
Mutex.h
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1 //===- llvm/Support/Mutex.h - Mutex Operating System Concept -----*- C++ -*-===//
2 //
3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4 // See https://llvm.org/LICENSE.txt for license information.
5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6 //
7 //===----------------------------------------------------------------------===//
8 //
9 // This file declares the llvm::sys::Mutex class.
10 //
11 //===----------------------------------------------------------------------===//
12 
13 #ifndef LLVM_SUPPORT_MUTEX_H
14 #define LLVM_SUPPORT_MUTEX_H
15 
16 #include "llvm/Config/llvm-config.h"
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  /// 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  /// Default Constructor.
37  explicit MutexImpl(bool recursive = true);
38 
39  /// Releases and removes the lock
40  /// 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  /// 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  /// 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  /// 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 {
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:85
This class represents lattice values for constants.
Definition: AllocatorList.h:23
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:95
SmartMutex< false > Mutex
Mutex - A standard, always enforced mutex.
Definition: Mutex.h:138
MutexImpl(bool recursive=true)
Initializes the lock but doesn&#39;t acquire it.
Definition: Mutex.cpp:44
place backedge safepoints impl
bool llvm_is_multithreaded()
Returns true if LLVM is compiled with support for multi-threading, and false otherwise.
Definition: Threading.cpp:30
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 Destructor.
Definition: Mutex.cpp:76
assert(ImpDefSCC.getReg()==AMDGPU::SCC &&ImpDefSCC.isDef())
bool tryacquire()
Attempts to acquire the lock without blocking.
Definition: Mutex.cpp:105