xpcom/base/StaticMutex.h@6474c204b198
xpcom/base/StaticMutex.h
Wed, 31 Dec 2014 06:09:35 +0100
- author
- Michael Schloh von Bennewitz <michael@schloh.com>
- date
- Wed, 31 Dec 2014 06:09:35 +0100
- changeset 0
- 6474c204b198
- permissions
- -rw-r--r--
Cloned upstream origin tor-browser at tor-browser-31.3.0esr-4.5-1-build1
revision ID fc1c9ff7c1b2defdbc039f12214767608f46423f for hacking purpose.
1 #ifndef mozilla_StaticMutex_h
2 #define mozilla_StaticMutex_h
4 #include "mozilla/Atomics.h"
5 #include "mozilla/Mutex.h"
7 namespace mozilla {
9 /**
10 * StaticMutex is a Mutex that can (and in fact, must) be used as a
11 * global/static variable.
12 *
13 * The main reason to use StaticMutex as opposed to
14 * StaticAutoPtr<OffTheBooksMutex> is that we instantiate the StaticMutex in a
15 * thread-safe manner the first time it's used.
16 *
17 * The same caveats that apply to StaticAutoPtr apply to StaticMutex. In
18 * particular, do not use StaticMutex as a stack variable or a class instance
19 * variable, because this class relies on the fact that global variablies are
20 * initialized to 0 in order to initialize mMutex. It is only safe to use
21 * StaticMutex as a global or static variable.
22 */
23 class StaticMutex
24 {
25 public:
26 // In debug builds, check that mMutex is initialized for us as we expect by
27 // the compiler. In non-debug builds, don't declare a constructor so that
28 // the compiler can see that the constructor is trivial.
29 #ifdef DEBUG
30 StaticMutex()
31 {
32 MOZ_ASSERT(!mMutex);
33 }
34 #endif
36 void Lock()
37 {
38 Mutex()->Lock();
39 }
41 void Unlock()
42 {
43 Mutex()->Unlock();
44 }
46 void AssertCurrentThreadOwns()
47 {
48 #ifdef DEBUG
49 Mutex()->AssertCurrentThreadOwns();
50 #endif
51 }
53 private:
54 OffTheBooksMutex* Mutex()
55 {
56 if (mMutex) {
57 return mMutex;
58 }
60 OffTheBooksMutex* mutex = new OffTheBooksMutex("StaticMutex");
61 if (!mMutex.compareExchange(nullptr, mutex)) {
62 delete mutex;
63 }
65 return mMutex;
66 }
68 Atomic<OffTheBooksMutex*> mMutex;
71 // Disallow copy constructor, but only in debug mode. We only define
72 // a default constructor in debug mode (see above); if we declared
73 // this constructor always, the compiler wouldn't generate a trivial
74 // default constructor for us in non-debug mode.
75 #ifdef DEBUG
76 StaticMutex(StaticMutex &other);
77 #endif
79 // Disallow these operators.
80 StaticMutex& operator=(StaticMutex* rhs);
81 static void* operator new(size_t) CPP_THROW_NEW;
82 static void operator delete(void*);
83 };
85 typedef BaseAutoLock<StaticMutex> StaticMutexAutoLock;
86 typedef BaseAutoUnlock<StaticMutex> StaticMutexAutoUnlock;
88 } // namespace mozilla
90 #endif
