141 lines
4.8 KiB
C++
141 lines
4.8 KiB
C++
// Filename: copyOnWritePointer.cxx
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// Created by: drose (09Apr07)
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//
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////////////////////////////////////////////////////////////////////
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//
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// PANDA 3D SOFTWARE
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// Copyright (c) 2001 - 2004, Disney Enterprises, Inc. All rights reserved
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//
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// All use of this software is subject to the terms of the Panda 3d
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// Software license. You should have received a copy of this license
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// along with this source code; you will also find a current copy of
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// the license at http://etc.cmu.edu/panda3d/docs/license/ .
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//
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// To contact the maintainers of this program write to
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// panda3d-general@lists.sourceforge.net .
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//
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////////////////////////////////////////////////////////////////////
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#include "copyOnWritePointer.h"
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#include "mutexHolder.h"
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#include "config_util.h"
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#include "config_pipeline.h"
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#ifdef COW_THREADED
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////////////////////////////////////////////////////////////////////
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// Function: CopyOnWritePointer::get_read_pointer
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// Access: Public
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// Description: Returns a pointer locked for read. Until this
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// pointer dereferences, calls to get_write_pointer()
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// will force a copy.
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//
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// This flavor of the method is written for the threaded
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// case.
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////////////////////////////////////////////////////////////////////
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CPT(CopyOnWriteObject) CopyOnWritePointer::
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get_read_pointer() const {
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if (_object == (CopyOnWriteObject *)NULL) {
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return NULL;
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}
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Thread *current_thread = Thread::get_current_thread();
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MutexHolder holder(_object->_lock_mutex);
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while (_object->_lock_status == CopyOnWriteObject::LS_locked_write) {
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if (_object->_locking_thread == current_thread) {
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return _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 " << _object->get_type()
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<< " " << _object << ", held by " << *_object->_locking_thread
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<< "\n";
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}
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_object->_lock_cvar.wait();
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}
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_object->_lock_status = CopyOnWriteObject::LS_locked_read;
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_object->_locking_thread = Thread::get_current_thread();
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return _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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// Function: CopyOnWritePointer::get_write_pointer
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// Access: Public
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// Description: Returns a pointer locked for write. If another
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// thread or threads already hold the pointer locked for
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// read, then this will force a copy.
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//
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// Until this pointer dereferences, calls to
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// get_read_pointer() or get_write_pointer() will block.
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//
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// This flavor of the method is written for the threaded
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// case.
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////////////////////////////////////////////////////////////////////
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PT(CopyOnWriteObject) CopyOnWritePointer::
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get_write_pointer() {
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if (_object == (CopyOnWriteObject *)NULL) {
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return NULL;
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}
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Thread *current_thread = Thread::get_current_thread();
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MutexHolder holder(_object->_lock_mutex);
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while (_object->_lock_status == CopyOnWriteObject::LS_locked_write &&
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_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 " << _object->get_type()
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<< " " << _object << ", held by " << *_object->_locking_thread
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<< "\n";
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}
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_object->_lock_cvar.wait();
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}
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if (_object->_lock_status == CopyOnWriteObject::LS_locked_read) {
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nassertr(_object->get_ref_count() > _object->get_cache_ref_count(), NULL);
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if (util_cat.is_debug()) {
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util_cat.debug()
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<< "Making copy of " << _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 = _object->make_cow_copy();
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cache_unref_delete(_object);
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_object = new_object;
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_object->cache_ref();
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} else if (_object->get_cache_ref_count() > 1) {
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// No one else has it specifically read-locked, but there are
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// other CopyOnWritePointers holding the same object, so we should
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// make our own 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 " << _object->get_type()
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<< " because it is shared by " << _object->get_ref_count()
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<< " pointers.\n";
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}
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PT(CopyOnWriteObject) new_object = _object->make_cow_copy();
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cache_unref_delete(_object);
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_object = new_object;
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_object->cache_ref();
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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
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// without making a copy.
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// We can't assert that there are no outstanding ordinary
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// references to it, though, since the creator of the object might
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// have saved himself a reference.
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}
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_object->_lock_status = CopyOnWriteObject::LS_locked_write;
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_object->_locking_thread = Thread::get_current_thread();
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return _object;
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}
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#endif // COW_THREADED
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