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/*
* Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be found
* in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#ifndef WEBRTC_SYSTEM_WRAPPERS_INCLUDE_STATIC_INSTANCE_H_
#define WEBRTC_SYSTEM_WRAPPERS_INCLUDE_STATIC_INSTANCE_H_
#include <assert.h>
#include "webrtc/system_wrappers/include/critical_section_wrapper.h"
#ifdef _WIN32
#include "webrtc/system_wrappers/include/fix_interlocked_exchange_pointer_win.h"
#endif
namespace webrtc {
enum CountOperation {
kRelease,
kAddRef,
kAddRefNoCreate
};
enum CreateOperation {
kInstanceExists,
kCreate,
kDestroy
};
template <class T>
// Construct On First Use idiom. Avoids
// "static initialization order fiasco".
static T* GetStaticInstance(CountOperation count_operation) {
// TODO (hellner): use atomic wrapper instead.
static volatile long instance_count = 0;
static T* volatile instance = NULL;
CreateOperation state = kInstanceExists;
#ifndef _WIN32
// This memory is staticly allocated once. The application does not try to
// free this memory. This approach is taken to avoid issues with
// destruction order for statically allocated memory. The memory will be
// reclaimed by the OS and memory leak tools will not recognize memory
// reachable from statics leaked so no noise is added by doing this.
static CriticalSectionWrapper* crit_sect(
CriticalSectionWrapper::CreateCriticalSection());
CriticalSectionScoped lock(crit_sect);
if (count_operation ==
kAddRefNoCreate && instance_count == 0) {
return NULL;
}
if (count_operation ==
kAddRef ||
count_operation == kAddRefNoCreate) {
instance_count++;
if (instance_count == 1) {
state = kCreate;
}
} else {
instance_count--;
if (instance_count == 0) {
state = kDestroy;
}
}
if (state == kCreate) {
instance = T::CreateInstance();
} else if (state == kDestroy) {
T* old_instance = instance;
instance = NULL;
// The state will not change past this point. Release the critical
// section while deleting the object in case it would be blocking on
// access back to this object. (This is the case for the tracing class
// since the thread owned by the tracing class also traces).
// TODO(hellner): this is a bit out of place but here goes, de-couple
// thread implementation with trace implementation.
crit_sect->Leave();
if (old_instance) {
delete old_instance;
}
// Re-acquire the lock since the scoped critical section will release
// it.
crit_sect->Enter();
return NULL;
}
#else // _WIN32
if (count_operation ==
kAddRefNoCreate && instance_count == 0) {
return NULL;
}
if (count_operation == kAddRefNoCreate) {
if (1 == InterlockedIncrement(&instance_count)) {
// The instance has been destroyed by some other thread. Rollback.
InterlockedDecrement(&instance_count);
assert(false);
return NULL;
}
// Sanity to catch corrupt state.
if (instance == NULL) {
assert(false);
InterlockedDecrement(&instance_count);
return NULL;
}
} else if (count_operation == kAddRef) {
if (instance_count == 0) {
state = kCreate;
} else {
if (1 == InterlockedIncrement(&instance_count)) {
// InterlockedDecrement because reference count should not be
// updated just yet (that's done when the instance is created).
InterlockedDecrement(&instance_count);
state = kCreate;
}
}
} else {
int new_value = InterlockedDecrement(&instance_count);
if (new_value == 0) {
state = kDestroy;
}
}
if (state == kCreate) {
// Create instance and let whichever thread finishes first assign its
// local copy to the global instance. All other threads reclaim their
// local copy.
T* new_instance = T::CreateInstance();
if (1 == InterlockedIncrement(&instance_count)) {
InterlockedExchangePointer(reinterpret_cast<void * volatile*>(&instance),
new_instance);
} else {
InterlockedDecrement(&instance_count);
if (new_instance) {
delete static_cast<T*>(new_instance);
}
}
} else if (state == kDestroy) {
T* old_value = static_cast<T*>(InterlockedExchangePointer(
reinterpret_cast<void * volatile*>(&instance), NULL));
if (old_value) {
delete static_cast<T*>(old_value);
}
return NULL;
}
#endif // #ifndef _WIN32
return instance;
}
} // namspace webrtc
#endif // WEBRTC_SYSTEM_WRAPPERS_INCLUDE_STATIC_INSTANCE_H_
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