141 lines
4.6 KiB
C++
141 lines
4.6 KiB
C++
/**
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* PANDA 3D SOFTWARE
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* Copyright (c) Carnegie Mellon University. All rights reserved.
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*
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* All use of this software is subject to the terms of the revised BSD
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* license. You should have received a copy of this license along
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* with this source code in a file named "LICENSE."
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*
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* @file copyOnWritePointer.cxx
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* @author drose
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* @date 2007-04-09
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*/
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#include "copyOnWritePointer.h"
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#include "config_putil.h"
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#include "config_pipeline.h"
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#ifdef COW_THREADED
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/**
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* Returns a pointer locked for read. Until this pointer dereferences, calls
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* to get_write_pointer() will force a copy.
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*
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* This flavor of the method is written for the threaded case.
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*/
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CPT(CopyOnWriteObject) CopyOnWritePointer::
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get_read_pointer(Thread *current_thread) const {
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if (_cow_object == nullptr) {
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return nullptr;
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}
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MutexHolder holder(_cow_object->_lock_mutex);
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while (_cow_object->_lock_status == CopyOnWriteObject::LS_locked_write) {
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if (_cow_object->_locking_thread == current_thread) {
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return _cow_object;
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}
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if (util_cat.is_debug()) {
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util_cat.debug()
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<< *current_thread << " waiting on " << _cow_object->get_type()
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<< " " << _cow_object << ", held by " << *_cow_object->_locking_thread
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<< "\n";
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}
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_cow_object->_lock_cvar.wait();
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}
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_cow_object->_lock_status = CopyOnWriteObject::LS_locked_read;
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_cow_object->_locking_thread = current_thread;
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return _cow_object;
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}
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#endif // COW_THREADED
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#ifdef COW_THREADED
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/**
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* Returns a pointer locked for write. If another thread or threads already
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* hold the pointer locked for read, then this will force a copy.
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*
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* Until this pointer dereferences, calls to get_read_pointer() or
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* get_write_pointer() will block.
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*
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* This flavor of the method is written for the threaded case.
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*/
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PT(CopyOnWriteObject) CopyOnWritePointer::
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get_write_pointer() {
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if (_cow_object == nullptr) {
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return nullptr;
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}
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Thread *current_thread = Thread::get_current_thread();
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_cow_object->_lock_mutex.lock();
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while (_cow_object->_lock_status == CopyOnWriteObject::LS_locked_write &&
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_cow_object->_locking_thread != current_thread) {
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if (util_cat.is_debug()) {
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util_cat.debug()
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<< *current_thread << " waiting on " << _cow_object->get_type()
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<< " " << _cow_object << ", held by " << *_cow_object->_locking_thread
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<< "\n";
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}
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_cow_object->_lock_cvar.wait();
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}
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if (_cow_object->_lock_status == CopyOnWriteObject::LS_locked_read) {
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nassertr(_cow_object->get_ref_count() > _cow_object->get_cache_ref_count(), nullptr);
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if (util_cat.is_debug()) {
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util_cat.debug()
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<< "Making copy of " << _cow_object->get_type()
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<< " because it is locked in read mode.\n";
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}
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PT(CopyOnWriteObject) new_object = _cow_object->make_cow_copy();
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_cow_object->CachedTypedWritableReferenceCount::cache_unref();
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_cow_object->_lock_mutex.unlock();
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MutexHolder holder(new_object->_lock_mutex);
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_cow_object = new_object;
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_cow_object->CachedTypedWritableReferenceCount::cache_ref();
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_cow_object->_lock_status = CopyOnWriteObject::LS_locked_write;
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_cow_object->_locking_thread = current_thread;
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return new_object;
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} else if (_cow_object->get_cache_ref_count() > 1) {
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// No one else has it specifically read-locked, but there are other
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// CopyOnWritePointers holding the same object, so we should make our own
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// writable copy anyway.
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if (util_cat.is_debug()) {
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util_cat.debug()
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<< "Making copy of " << _cow_object->get_type()
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<< " because it is shared by " << _cow_object->get_ref_count()
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<< " pointers.\n";
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}
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PT(CopyOnWriteObject) new_object = _cow_object->make_cow_copy();
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_cow_object->CachedTypedWritableReferenceCount::cache_unref();
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_cow_object->_lock_mutex.unlock();
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MutexHolder holder(new_object->_lock_mutex);
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_cow_object = new_object;
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_cow_object->CachedTypedWritableReferenceCount::cache_ref();
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_cow_object->_lock_status = CopyOnWriteObject::LS_locked_write;
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_cow_object->_locking_thread = current_thread;
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return new_object;
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} else {
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// No other thread has the pointer locked, and we're the only
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// CopyOnWritePointer with this object. We can safely write to it without
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// making a copy.
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// We can't assert that there are no outstanding ordinary references to
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// it, though, since the creator of the object might have saved himself a
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// reference.
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_cow_object->_lock_status = CopyOnWriteObject::LS_locked_write;
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_cow_object->_locking_thread = current_thread;
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_cow_object->_lock_mutex.unlock();
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}
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return _cow_object;
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}
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#endif // COW_THREADED
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