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Diffstat (limited to 'java/src/Token.java')
| -rw-r--r-- | java/src/Token.java | 298 |
1 files changed, 0 insertions, 298 deletions
diff --git a/java/src/Token.java b/java/src/Token.java deleted file mode 100644 index a17be013ad5..00000000000 --- a/java/src/Token.java +++ /dev/null @@ -1,298 +0,0 @@ -/************************************************* - * - * = PACKAGE - * JACE.Concurrency - * - * = FILENAME - * Token.java - * - *@author Prashant Jain - * - *************************************************/ -package JACE.Concurrency; - -import java.util.*; -import JACE.ASX.*; - -class WaitObject extends TimedWait -{ - public boolean condition () - { - return this.condition_; - } - - public void condition (boolean c) - { - this.condition_ = c; - } - - private boolean condition_ = false; -} - -/** - * <hr> - * <h2>SYNOPSIS</h2> - *<blockquote> - * Class that acquires, renews, and releases a synchronization - * token that is serviced in strict FIFO ordering. - * - *</blockquote> - * - * <h2>DESCRIPTION</h2> - *<blockquote> - * This is a general-purpose synchronization mechanism that offers - * several benefits. For example, it implements "recursive mutex" - * semantics, where a thread that owns the token can reacquire it - * without deadlocking. In addition, threads that are blocked - * awaiting the token are serviced in strict FIFO order as other - * threads release the token. The solution makes use of the - * Specific Notification pattern presented by Tom Cargill in - * "Specific Notification for Java Thread Synchronization," PLoP96. - *</blockquote> - */ -public class Token -{ - /** - * Acquire the token. Note that this will block. The method uses - * synchronized blocks internally to avoid race conditions. - *@return 0 if acquires without calling <sleepHook> - * 1 if <sleepHook> is called. - * -1 if failure occurs - *@exception InterruptedException exception during wait - */ - public int acquire () throws InterruptedException - { - try - { - return this.acquire (new TimeValue ()); - } - catch (TimeoutException e) - { - // This really shouldn't happen since we are supposed to - // block. - return -1; - } - } - - /** - * Acquire the token. Wait for timeout amount of time. The method - * uses synchronized blocks internally to avoid race conditions. - *@param timeout Amount of time to wait for in trying to acquire the - * token. - *@return 0 if acquires without calling <sleepHook> - * 1 if <sleepHook> is called. - * -1 if failure occurs - *@exception TimeoutException exception if timeout occurs - *@exception InterruptedException exception during wait - */ - public int acquire (TimeValue timeout) throws InterruptedException, TimeoutException - { - int result = 0; - WaitObject snl = new WaitObject (); - boolean mustWait; - synchronized (snl) - { - synchronized (this) - { - mustWait = !this.snq_.isEmpty (); - if (mustWait && - Thread.currentThread ().toString ().compareTo (this.owner_) == 0) - { - // I am the one who has the token. So just increment - // the nesting level - this.nestingLevel_++; - return result; - } - // Add local lock to the queue - this.snq_.addElement (snl); - } - if (mustWait) - { - result = 1; - // Call sleep hook - sleepHook (); - snl.timedWait (timeout); // Do a blocking wait - } - // Set the owner of the token - this.owner_ = Thread.currentThread ().toString (); - } - return result; - } - - /** - * Try to acquire the token. Implements a non-blocking acquire. - *@return 0 if acquires without calling <sleepHook> - * 1 if <sleepHook> is called. - * -1 if failure occurs - */ - public synchronized int tryAcquire () - { - int result = 0; - if (!this.snq_.isEmpty ()) - { - // No one has the token, so acquire it - this.snq_.addElement (new WaitObject ()); - } - // Check if I am the one holding the token. - else if (Thread.currentThread ().toString ().compareTo (this.owner_) == 0) - { - this.nestingLevel_++; - } - // Someone else has the token. - else - { - // Will have to block to acquire the token, so call - // sleepHook and return - sleepHook (); - result = 1; - } - return result; - } - - /** - * Method that is called before a thread goes to sleep in an - * acquire(). This should be overridden by a subclass to define - * the appropriate behavior before acquire() goes to sleep. - * By default, this is a no-op. - */ - public void sleepHook () - { - } - - /** - * An optimized method that efficiently reacquires the token if no - * other threads are waiting. This is useful for situations where - * you don't want to degrade the quality of service if there are - * other threads waiting to get the token. - *@param requeuePosition Position in the queue where to insert the - * lock. If requeuePosition == -1 and there are other threads - * waiting to obtain the token we are queued at the end of the list - * of waiters. If requeuePosition > -1 then it indicates how many - * entries to skip over before inserting our thread into the list of - * waiters (e.g.,requeuePosition == 0 means "insert at front of the - * queue"). - *@exception InterruptedException exception during wait - */ - public void renew (int requeuePosition) throws InterruptedException - { - try - { - this.renew (requeuePosition, new TimeValue ()); - } - catch (TimeoutException e) - { - // This really shouldn't happen since we are supposed to - // block. - } - } - - /** - * An optimized method that efficiently reacquires the token if no - * other threads are waiting. This is useful for situations where - * you don't want to degrade the quality of service if there are - * other threads waiting to get the token. - *@param requeuePosition Position in the queue where to insert the - * lock. If requeuePosition == -1 and there are other threads - * waiting to obtain the token we are queued at the end of the list - * of waiters. If requeuePosition > -1 then it indicates how many - * entries to skip over before inserting our thread into the list of - * waiters (e.g.,requeuePosition == 0 means "insert at front of the - * queue"). - *@param timeout Amount of time to wait for in trying to acquire the - * token. - *@exception TimeoutException exception if timeout occurs - *@exception InterruptedException exception during wait - */ - public void renew (int requeuePosition, TimeValue timeout) - throws InterruptedException, TimeoutException - { - WaitObject snl = null; - int saveNestingLevel = 0; - - synchronized (this) - { - // Check if there is a thread waiting to acquire the token. If - // not or if requeuePosition == 0, then we don't do anything - // and we simply keep the token. - if (this.snq_.size () > 1 && requeuePosition != 0) - { - // Save the nesting level - saveNestingLevel = this.nestingLevel_; - this.nestingLevel_ = 0; - - // Reinsert ourselves at requeuePosition in the queue - snl = (WaitObject) this.snq_.firstElement (); - this.snq_.removeElementAt (0); - - if (requeuePosition < 0) - this.snq_.addElement (snl); // Insert at end - else - this.snq_.insertElementAt (snl, requeuePosition); - - synchronized (this.snq_.firstElement ()) - { - // Notify the first waiting thread in the queue - WaitObject obj = (WaitObject) this.snq_.firstElement (); - // Set its condition to be true so that it falls out - // of the for loop - obj.condition (true); - // Now signal the thread - obj.signal (); - } - } - } - - // Check if we reinserted the lock in the queue and therefore need - // to do a wait - if (snl != null) - { - synchronized (snl) - { - // Set the condition to be false so that we can begin the - // wait - snl.condition (false); - // Do a blocking wait - snl.timedWait (timeout); - } - // Restore the nesting level and current owner of the lock - this.nestingLevel_ = saveNestingLevel; - this.owner_ = Thread.currentThread ().toString (); - } - } - - /** - * Release the token. - */ - public synchronized void release () - { - // Check if nestingLevel > 0 and if so, decrement it - if (this.nestingLevel_ > 0) - this.nestingLevel_--; - else - { - this.snq_.removeElementAt (0); - if (!this.snq_.isEmpty ()) - { - synchronized (this.snq_.firstElement ()) - { - // Notify the first waiting thread in the queue - WaitObject obj = (WaitObject) this.snq_.firstElement (); - // Set its condition to be true so that it falls out - // of the for loop - obj.condition (true); - // Now signal the thread - obj.signal (); - } - } - } - } - - private Vector snq_ = new Vector (); - // Vector of lock objects - - private int nestingLevel_ = 0; - // Current Nesting Level - - private String owner_ = null; - // Current owner of the token. -} |