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) :
impl(rec)97         impl(rec), acquired(0), recursive(rec) { }
98 
lock()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 
unlock()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 
try_lock()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:
SmartScopedLock(SmartMutex<mt_only> & m)145       SmartScopedLock(SmartMutex<mt_only>& m) : mtx(m) {
146         mtx.lock();
147       }
148 
~SmartScopedLock()149       ~SmartScopedLock() {
150         mtx.unlock();
151       }
152     };
153 
154     typedef SmartScopedLock<false> ScopedLock;
155   }
156 }
157 
158 #endif
159