EnvironmentDelegate.cpp

/*******************************************************************************
 * Copyright IBM Corp. and others 2017
 *
 * This program and the accompanying materials are made available under
 * the terms of the Eclipse Public License 2.0 which accompanies this
 * distribution and is available at https://www.eclipse.org/legal/epl-2.0/
 * or the Apache License, Version 2.0 which accompanies this distribution
 * and is available at https://www.apache.org/licenses/LICENSE-2.0.
 *
 * This Source Code may also be made available under the following Secondary
 * Licenses when the conditions for such availability set forth in the
 * Eclipse Public License, v. 2.0 are satisfied: GNU General Public License,
 * version 2 with the GNU Classpath Exception [1] and GNU General Public
 * License, version 2 with the OpenJDK Assembly Exception [2].
 *
 * [1] https://www.gnu.org/software/classpath/license.html
 * [2] https://openjdk.org/legal/assembly-exception.html
 *
 * SPDX-License-Identifier: EPL-2.0 OR Apache-2.0 OR GPL-2.0-only WITH Classpath-exception-2.0 OR GPL-2.0-only WITH OpenJDK-assembly-exception-1.0
 *******************************************************************************/

#include "ModronAssertions.h"
#include "omr.h"
#include "omrExampleVM.hpp"

#include "AtomicOperations.hpp"
#include "EnvironmentStandard.hpp"
#include "EnvironmentDelegate.hpp"
#include "GCExtensionsBase.hpp"
#include "SublistFragment.hpp"

OMR_VMThread *
MM_EnvironmentDelegate::attachVMThread(OMR_VM *omrVM, const char *threadName, uintptr_t reason)
{
	OMR_VMThread *omrVMThread = NULL;
	omr_error_t rc = OMR_ERROR_NONE;

	rc = OMR_Glue_BindCurrentThread(omrVM, threadName, &omrVMThread);
	if (OMR_ERROR_NONE != rc) {
		return NULL;
	}
	return omrVMThread;
}

void
MM_EnvironmentDelegate::detachVMThread(OMR_VM *omrVM, OMR_VMThread *omrVMThread, uintptr_t reason)
{
	if (NULL != omrVMThread) {
		OMR_Glue_UnbindCurrentThread(omrVMThread);
	}
}

void
MM_EnvironmentDelegate::acquireVMAccess()
{
	OMR_VM_Example *exampleVM = (OMR_VM_Example *)_env->getOmrVM()->_language_vm;
	omrthread_rwmutex_enter_read(exampleVM->_vmAccessMutex);
}

/**
 * Release shared VM acccess.
 */
void
MM_EnvironmentDelegate::releaseVMAccess()
{
	OMR_VM_Example *exampleVM = (OMR_VM_Example *)_env->getOmrVM()->_language_vm;
	omrthread_rwmutex_exit_read(exampleVM->_vmAccessMutex);
}

/**
 * Check whether another thread is requesting exclusive VM access. This method must be
 * called frequently by all threads that are holding shared VM access. If this method
 * returns true, the calling thread should release shared VM access as quickly as possible
 * and reacquire it if necessary.

 * @return true if another thread is waiting to acquire exclusive VM access
 */
bool
MM_EnvironmentDelegate::isExclusiveAccessRequestWaiting()
{
	OMR_VM_Example *exampleVM = (OMR_VM_Example *)_env->getOmrVM()->_language_vm;
	if ((0 < exampleVM->_vmExclusiveAccessCount) || omrthread_rwmutex_is_writelocked(exampleVM->_vmAccessMutex)) {
		return true;
	}
	if (NULL != _env->getExtensions()->gcExclusiveAccessThreadId) {
		return true;
	}
	return false;
}

/**
 * Acquire exclusive VM access. This method should only be called by the OMR runtime to
 * perform stop-the-world operations such as garbage collection. Calling thread will be
 * blocked until all other threads holding shared VM access have release VM access.
 */
void
MM_EnvironmentDelegate::acquireExclusiveVMAccess()
{
	if (0 == _env->getOmrVMThread()->exclusiveCount) {
		OMR_VM *omrVM = _env->getOmrVM();
		OMR_VM_Example *exampleVM = (OMR_VM_Example *)omrVM->_language_vm;

		/* tell the rest of the world that a thread is going for exclusive VM< access */
		MM_AtomicOperations::add(&exampleVM->_vmExclusiveAccessCount, 1);

		/* unconditionally acquire exclusive VM access by locking the VM thread list mutex */
		omrthread_rwmutex_enter_write(exampleVM->_vmAccessMutex);
		omrthread_monitor_enter(omrVM->_vmThreadListMutex);
	}
	_env->getOmrVMThread()->exclusiveCount += 1;
}

/**
 * Release exclusive VM acccess. If no other thread is waiting for exclusive VM access
 * this method will notify all threads waiting for shared VM access to continue and
 * acquire shared VM access.
 */
void
MM_EnvironmentDelegate::releaseExclusiveVMAccess()
{
	if (1 == _env->getOmrVMThread()->exclusiveCount) {
		OMR_VM_Example *exampleVM = (OMR_VM_Example *)_env->getOmrVM()->_language_vm;
		omrthread_monitor_exit(_env->getOmrVM()->_vmThreadListMutex);
		omrthread_rwmutex_exit_write(exampleVM->_vmAccessMutex);
		Assert_MM_true(0 < exampleVM->_vmExclusiveAccessCount);
		MM_AtomicOperations::subtract(&exampleVM->_vmExclusiveAccessCount, 1);
		_env->getOmrVMThread()->exclusiveCount -= 1;
	} else if (1 < _env->getOmrVMThread()->exclusiveCount) {
		_env->getOmrVMThread()->exclusiveCount -= 1;
	}
}

/**
 * Give up exclusive access in preparation for transferring it to a collaborating thread
 * (i.e. collaborator-to-main or main-to-collaborator). This may involve nothing more than
 * transferring OMR_VMThread::exclusiveCount from the owning thread to the another
 * thread that thereby assumes exclusive access. Implement if this kind of collaboration
 * is required.
 *
 * @return the exclusive count of the current thread before relinquishing
 * @see assumeExclusiveVMAccess(uintptr_t)
 */
uintptr_t
MM_EnvironmentDelegate::relinquishExclusiveVMAccess()
{
	uintptr_t relinquishedExclusiveCount = _env->getOmrVMThread()->exclusiveCount;
	_env->getOmrVMThread()->exclusiveCount = 0;
	return relinquishedExclusiveCount;
}

/**
 * Assume exclusive access from a collaborating thread (i.e. collaborator-to-main or main-to-collaborator).
 * Implement if this kind of collaboration is required.
 *
 * @param exclusiveCount the exclusive count to be restored
 * @see relinquishExclusiveVMAccess()
 */
void
MM_EnvironmentDelegate::assumeExclusiveVMAccess(uintptr_t exclusiveCount)
{
	_env->getOmrVMThread()->exclusiveCount = exclusiveCount;
}