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       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 &) = delete;
80       void operator=(const MutexImpl &) = delete;
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 {
90       MutexImpl impl;
91       unsigned acquired;
92       bool recursive;
93     public:
94       explicit SmartMutex(bool rec = true) :
impl(rec)95         impl(rec), acquired(0), recursive(rec) { }
96 
lock()97       bool lock() {
98         if (!mt_only || llvm_is_multithreaded()) {
99           return impl.acquire();
100         } else {
101           // Single-threaded debugging code.  This would be racy in
102           // multithreaded mode, but provides not sanity checks in single
103           // threaded mode.
104           assert((recursive || acquired == 0) && "Lock already acquired!!");
105           ++acquired;
106           return true;
107         }
108       }
109 
unlock()110       bool unlock() {
111         if (!mt_only || llvm_is_multithreaded()) {
112           return impl.release();
113         } else {
114           // Single-threaded debugging code.  This would be racy in
115           // multithreaded mode, but provides not sanity checks in single
116           // threaded mode.
117           assert(((recursive && acquired) || (acquired == 1)) &&
118                  "Lock not acquired before release!");
119           --acquired;
120           return true;
121         }
122       }
123 
try_lock()124       bool try_lock() {
125         if (!mt_only || llvm_is_multithreaded())
126           return impl.tryacquire();
127         else return true;
128       }
129 
130       private:
131         SmartMutex(const SmartMutex<mt_only> & original);
132         void operator=(const SmartMutex<mt_only> &);
133     };
134 
135     /// Mutex - A standard, always enforced mutex.
136     typedef SmartMutex<false> Mutex;
137 
138     template<bool mt_only>
139     class SmartScopedLock  {
140       SmartMutex<mt_only>& mtx;
141 
142     public:
SmartScopedLock(SmartMutex<mt_only> & m)143       SmartScopedLock(SmartMutex<mt_only>& m) : mtx(m) {
144         mtx.lock();
145       }
146 
~SmartScopedLock()147       ~SmartScopedLock() {
148         mtx.unlock();
149       }
150     };
151 
152     typedef SmartScopedLock<false> ScopedLock;
153   }
154 }
155 
156 #endif
157