Mega Code Archive
0401 The Lock Methods
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void lock( )
Waits until the invoking lock can be acquired.
void lockInterruptibly( ) throws InterruptedException
Waits until the invoking lock can be acquired, unless interrupted.
Condition newCondition( )
Returns a Condition object that is associated with the invoking lock.
boolean tryLock( )
Attempts to acquire the lock. This method will not wait if the lock is unavailable. Instead, it returns true if the lock has been acquired and false if the lock is currently in use by another thread.
boolean tryLock(long wait, TimeUnit tu) throws InterruptedException
Attempts to acquire the lock. If the lock is unavailable, this method will wait no longer than the period specified by wait, which is in tu units. It returns true if the lock has been acquired and false if the lock cannot be acquired within the specified period.
void unlock( )
Releases the lock.
/*
License for Java 1.5 'Tiger': A Developer's Notebook
(O'Reilly) example package
Java 1.5 'Tiger': A Developer's Notebook (O'Reilly)
by Brett McLaughlin and David Flanagan.
ISBN: 0-596-00738-8
You can use the examples and the source code any way you want, but
please include a reference to where it comes from if you use it in
your own products or services. Also note that this software is
provided by the author "as is", with no expressed or implied warranties.
In no event shall the author be liable for any direct or indirect
damages arising in any way out of the use of this software.
*/
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;
class LinkList<E> {
// The value of this node
E value;
// The rest of the list
LinkList<E> rest;
// A lock for this node
Lock lock;
// Signals when the value of this node changes
Condition valueChanged;
// Signals when the node this is connected to changes
Condition linkChanged;
public LinkList(E value) {
this.value = value;
rest = null;
lock = new ReentrantLock();
valueChanged = lock.newCondition();
linkChanged = lock.newCondition();
}
public void setValue(E value) {
lock.lock();
try {
this.value = value;
// Let waiting threads that the value has changed
valueChanged.signalAll();
} finally {
lock.unlock();
}
}
public void executeOnValue(E desiredValue, Runnable task)
throws InterruptedException {
lock.lock();
try {
// Checks the value against the desired value
while (!value.equals(desiredValue)) {
// This will wait until the value changes
valueChanged.await();
}
// When we get here, the value is correct -- Run the task
task.run();
} finally {
lock.unlock();
}
}
public void append(E value) {
// Start the pointer at this node
LinkList<E> node = this;
node.lock.lock();
while (node.rest != null) {
LinkList<E> next = node.rest;
// Here's the hand-over-hand locking
try {
// Lock the next node
next.lock.lock();
} finally {
// unlock the current node
node.lock.unlock();
}
// Traverse
node = next;
}
// We're at the final node, so append and then unlock
try {
node.rest = new LinkList<E>(value);
// Let any waiting threads know that this node's link has changed
node.linkChanged.signalAll();
} finally {
node.lock.unlock();
}
}
public void printUntilInterrupted(String prefix) {
// Start the pointer at this node
LinkList<E> node = this;
node.lock.lock();
while (true) {
LinkList<E> next;
try {
System.out.println(prefix + ": " + node.value);
// Wait for the next node if not available
while (node.rest == null) {
node.linkChanged.await();
}
// Get the next node
next = node.rest;
// Lock it - more hand-to-hand locking
next.lock.lock();
} catch (InterruptedException e) {
// reset the interrupt status
Thread.currentThread().interrupt();
return;
} finally {
node.lock.unlock();
}
// Traverse
node = next;
}
}
}
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