1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
3 /* This Source Code Form is subject to the terms of the Mozilla Public
4  * License, v. 2.0. If a copy of the MPL was not distributed with this
5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
6 
7 #ifndef threading_Mutex_h
8 #define threading_Mutex_h
9 
10 #include "mozilla/Assertions.h"
11 #include "mozilla/Attributes.h"
12 #include "mozilla/Move.h"
13 #include "mozilla/ThreadLocal.h"
14 #include "mozilla/Vector.h"
15 
16 #include <new>
17 #include <string.h>
18 
19 namespace js {
20 
21 class ConditionVariable;
22 
23 namespace detail {
24 
25 class MutexImpl
26 {
27 public:
28   struct PlatformData;
29 
30   MutexImpl();
31   ~MutexImpl();
32 
MutexImpl(MutexImpl && rhs)33   MutexImpl(MutexImpl&& rhs)
34     : platformData_(rhs.platformData_)
35   {
36     MOZ_ASSERT(this != &rhs, "self move disallowed!");
37     rhs.platformData_ = nullptr;
38   }
39 
40   MutexImpl& operator=(MutexImpl&& rhs) {
41     this->~MutexImpl();
42     new (this) MutexImpl(mozilla::Move(rhs));
43     return *this;
44   }
45 
46   bool operator==(const MutexImpl& rhs) {
47     return platformData_ == rhs.platformData_;
48   }
49 
50 protected:
51   void lock();
52   void unlock();
53 
54 private:
55   MutexImpl(const MutexImpl&) = delete;
56   void operator=(const MutexImpl&) = delete;
57 
58   friend class js::ConditionVariable;
platformData()59   PlatformData* platformData() {
60     MOZ_ASSERT(platformData_);
61     return platformData_;
62   };
63 
64   PlatformData* platformData_;
65 };
66 
67 } // namespace detail
68 
69 // A MutexId secifies the name and mutex order for a mutex.
70 //
71 // The mutex order defines the allowed order of mutex acqusition on a single
72 // thread. Mutexes must be acquired in strictly increasing order. Mutexes with
73 // the same order may not be held at the same time by that thread.
74 struct MutexId
75 {
76   const char* name;
77   uint32_t order;
78 };
79 
80 #ifndef DEBUG
81 
82 class Mutex : public detail::MutexImpl
83 {
84 public:
Init()85   static bool Init() { return true; }
ShutDown()86   static void ShutDown() {}
87 
Mutex(const MutexId & id)88   explicit Mutex(const MutexId& id) {}
89 
90   using MutexImpl::lock;
91   using MutexImpl::unlock;
92 };
93 
94 #else
95 
96 // In debug builds, js::Mutex is a wrapper over MutexImpl that checks correct
97 // locking order is observed.
98 //
99 // The class maintains a per-thread stack of currently-held mutexes to enable it
100 // to check this.
101 class Mutex : public detail::MutexImpl
102 {
103 public:
104   static bool Init();
105   static void ShutDown();
106 
Mutex(const MutexId & id)107   explicit Mutex(const MutexId& id)
108    : id_(id)
109   {
110     MOZ_ASSERT(id_.order != 0);
111   }
112 
113   void lock();
114   void unlock();
115 
116 private:
117   const MutexId id_;
118 
119   using MutexVector = mozilla::Vector<const Mutex*>;
120   static MOZ_THREAD_LOCAL(MutexVector*) HeldMutexStack;
121   static MutexVector& heldMutexStack();
122 };
123 
124 #endif
125 
126 } // namespace js
127 
128 #endif // threading_Mutex_h
129