gov.nist.javax.sip.stack.KeyedSemaphore Maven / Gradle / Ivy
/*
* Conditions Of Use
*
* This software was developed by employees of the National Institute of
* Standards and Technology (NIST), an agency of the Federal Government.
* Pursuant to title 15 Untied States Code Section 105, works of NIST
* employees are not subject to copyright protection in the United States
* and are considered to be in the public domain. As a result, a formal
* license is not needed to use the software.
*
* This software is provided by NIST as a service and is expressly
* provided "AS IS." NIST MAKES NO WARRANTY OF ANY KIND, EXPRESS, IMPLIED
* OR STATUTORY, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTY OF
* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, NON-INFRINGEMENT
* AND DATA ACCURACY. NIST does not warrant or make any representations
* regarding the use of the software or the results thereof, including but
* not limited to the correctness, accuracy, reliability or usefulness of
* the software.
*
* Permission to use this software is contingent upon your acceptance
* of the terms of this agreement
*
* .
*
*/
package android.gov.nist.javax.sip.stack;
import android.gov.nist.core.CommonLogger;
import android.gov.nist.core.StackLogger;
import java.io.IOException;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
public final class KeyedSemaphore {
private final ConcurrentHashMap map = new ConcurrentHashMap();
private static final StackLogger logger = CommonLogger.getLogger(KeyedSemaphore.class);
public void leaveIOCriticalSection(String key) {
Lock creationLock = map.get(key);
if (creationLock != null) {
creationLock.unlock();
if (logger.isLoggingEnabled(StackLogger.TRACE_DEBUG)) {
logger.logDebug("sem unlocked:" + creationLock);
}
}
}
/**
* It is assumed the current thread has locked the lock previously. Under
* this assumption is safer to unlock after removal, so any blocked thread
* on waiting removed block may proceed without timeout.
*
* Only remove if no other threads are already waiting on this lock, otherwise
* unexpected behaviour may arise by locking one lock object, and trying to release
* another instance of lock for the same key.
*
* @param key
*/
public void remove(String key) {
ReentrantLock myLock = map.get(key);
if (myLock != null &&
!myLock.hasQueuedThreads() && myLock.isHeldByCurrentThread()) {
map.remove(key);
logger.logDebug("sem removed:" + myLock);
//This lock is no longer reacheable
//remove all locks since this thread wont be able to unlock those anymore.
while (myLock.isHeldByCurrentThread() && myLock.getHoldCount() > 0) {
logger.logDebug("unlocking after remove:" + myLock);
myLock.unlock();
}
}//if there are other threads waiting on this semaphore let them reuse it
//so unwanted side effects are prevented
}
public void enterIOCriticalSection(String key) throws IOException {
// http://dmy999.com/article/34/correct-use-of-concurrenthashmap
Lock creationLock = map.get(key);
if (creationLock == null) {
ReentrantLock newCreationLock = new ReentrantLock(true);
creationLock = map.putIfAbsent(key, newCreationLock);
if (creationLock == null) {
creationLock = newCreationLock;
if (logger.isLoggingEnabled(StackLogger.TRACE_DEBUG)) {
logger.logDebug("new Semaphore added for key: " + key);
}
}
}
try {
boolean retval = creationLock.tryLock(10, TimeUnit.SECONDS);
if (!retval) {
throw new IOException("Could not acquire IO Semaphore'" + key
+ "' after 10 seconds -- giving up ");
}
} catch (InterruptedException e) {
throw new IOException("exception in acquiring sem");
}
}
public int getNumberOfSemaphores() {
return map.size();
}
}