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