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/*
* Copyright 2016 Google Inc. All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#ifndef BASE_THREADING_THREAD_LOCAL_OBJECT_H_
#define BASE_THREADING_THREAD_LOCAL_OBJECT_H_
#include <set>
#include "starboard/configuration.h"
#include "starboard/log.h"
#include "starboard/mutex.h"
#include "starboard/thread.h"
namespace base {
// Like base::ThreadLocalPointer<T> but destroys objects. This is important
// for using ThreadLocalObjects that aren't tied to a singleton, or for
// access by threads which will call join().
//
// FEATURE COMPARISON TABLE:
// | Thread Join | Container Destroyed
// ------------------------------------------------------------------
// ThreadLocalPointer<T> | LEAKS | LEAKS
// ThreadLocalObject<T> | Object Destroyed | Objects Destroyed
//
// EXAMPLE:
// ThreadLocalObject<std::map<std::string, int> > map_tls;
// Map* map = map_tls->GetOrCreate();
// (*map)["my string"] = 15;
// Thread t = new Thread(&map_tls);
// t->start();
// // t creates it's own thread local map.
// t->join(); // Make sure that thread joins before map_tls is destroyed!
//
// OBJECT DESTRUCTION:
// There are two ways for an object to be destroyed by the ThreadLocalObject.
// The first way is via a thread join. In this case only the object
// associated with the thread is deleted.
// The second way an object is destroyed is by the ThreadLocalObject
// container to be destroyed, in this case ALL thread local objects are
// destroyed.
//
// PERFORMANCE:
// ThreadLocalObject is fast for the Get() function if the object has
// has already been created, requiring one extra pointer dereference
// over ThreadLocalPointer<T>.
template <typename Type>
class ThreadLocalObject {
public:
ThreadLocalObject() : slot_() {
slot_ = SbThreadCreateLocalKey(DeleteEntry);
SB_DCHECK(kSbThreadLocalKeyInvalid != slot_);
constructing_thread_id_ = SbThreadGetId();
}
// Enables destruction by any other thread. Otherwise, the class instance
// will warn when a different thread than the constructing destroys this.
void EnableDestructionByAnyThread() {
constructing_thread_id_ = kSbThreadInvalidId;
}
// Thread Local Objects are destroyed after this call.
~ThreadLocalObject() {
CheckCurrentThreadAllowedToDestruct();
SB_DCHECK(entry_set_.size() < 2)
<< "Logic error: Some threads may still be accessing the objects that "
<< "are about to be destroyed. Only one object is expected and that "
<< "should be for the main thread. The caller should ensure that "
<< "other threads that access this object are externally "
<< "synchronized.";
// No locking is done because the entries should not be accessed by
// different threads while this object is shutting down. If access is
// occuring then the caller has a race condition, external to this class.
typedef typename Set::iterator Iter;
for (Iter it = entry_set_.begin(); it != entry_set_.end(); ++it) {
Entry* entry = *it;
SB_DCHECK(entry->owner_ == this);
delete entry->ptr_;
delete entry;
}
// Cleanup the thread local key.
SbThreadDestroyLocalKey(slot_);
}
// Warns if there is a misuse of this object.
void CheckCurrentThreadAllowedToDestruct() const {
if (kSbThreadInvalidId == constructing_thread_id_) {
return; // EnableDestructionByAnyThread() called.
}
const SbThreadId curr_thread_id = SbThreadGetId();
if (curr_thread_id == constructing_thread_id_) {
return; // Same thread that constructed this.
}
if (SB_DLOG_IS_ON(FATAL)) {
SB_DCHECK(false)
<< "ThreadLocalObject<T> was created in thread "
<< constructing_thread_id_ << "\nbut was destroyed by "
<< curr_thread_id << ". If this is intentional then call "
<< "EnableDestructionByAnyThread() to silence this "
<< "warning.";
}
}
// Either returns the created pointer for the current thread, or otherwise
// constructs the object using the default constructor and returns it.
Type* GetOrCreate() {
Type* object = GetIfExists();
if (!object) { // create object.
object = new Type();
Entry* entry = new Entry(this, object);
// Insert into the set of tls entries.
// Performance: Its assumed that creation of objects is much less
// frequent than getting an object.
{
starboard::ScopedLock lock(entry_set_mutex_);
entry_set_.insert(entry);
}
SbThreadSetLocalValue(slot_, entry);
}
return object;
}
// Returns the pointer if it exists in the current thread, otherwise NULL.
Type* GetIfExists() const {
Entry* entry = GetEntryIfExists();
if (!entry) { return NULL; }
return entry->ptr_;
}
// Releases ownership of the pointer FROM THE CURRENT THREAD.
// The caller has responsibility to make sure that the pointer is destroyed.
Type* Release() {
if (Entry* entry = GetEntryIfExists()) {
// The entry will no longer run it's destructor on thread join.
SbThreadSetLocalValue(slot_, NULL); // NULL out pointer for TLS.
Type* object = entry->ptr_;
RemoveEntry(entry);
return object;
} else {
return NULL;
}
}
private:
struct Entry {
Entry(ThreadLocalObject* own, Type* ptr) : owner_(own), ptr_(ptr) {
}
~Entry() {
ptr_ = NULL;
owner_ = NULL;
}
ThreadLocalObject* owner_;
Type* ptr_;
};
// Deletes the TLSEntry.
static void DeleteEntry(void* ptr) {
if (!ptr) {
SB_NOTREACHED();
return;
}
Entry* entry = reinterpret_cast<Entry*>(ptr);
ThreadLocalObject* tls = entry->owner_;
Type* object = entry->ptr_;
tls->RemoveEntry(entry);
delete object;
}
void RemoveEntry(Entry* entry) {
{
starboard::ScopedLock lock(entry_set_mutex_);
entry_set_.erase(entry);
}
delete entry;
}
Entry* GetEntryIfExists() const {
void* ptr = SbThreadGetLocalValue(slot_);
Entry* entry = static_cast<Entry*>(ptr);
return entry;
}
typedef std::set<Entry*> Set;
// Allows GetIfExists() to be const.
mutable SbThreadLocalKey slot_;
// entry_set_ contains all the outstanding entries for the thread local
// objects that have been created.
Set entry_set_;
mutable starboard::Mutex entry_set_mutex_;
// Used to warn when there is a mismatch between thread that constructed and
// thread that destroyed this object.
SbThreadId constructing_thread_id_;
SB_DISALLOW_COPY_AND_ASSIGN(ThreadLocalObject<Type>);
};
} // namespace base
#endif // BASE_THREADING_THREAD_LOCAL_H_