com.tangosol.util
Class ThreadGate

java.lang.Object
  com.tangosol.util.Base
      com.tangosol.util.ThreadGate

public class ThreadGate
extends Base

Use this class in cases that large numbers of threads can operate concurrently with an additional requirement that all threads be blocked for certain operations. The algorithm is based on a gate concept, allowing threads in (enter) and out (exit), but occasionally shutting the gate (close) such that other threads cannot enter and exit. However, since threads may "be inside", the gate cannot fully close until they leave (exit). Once all threads are out, the gate is closed, and can be re-opened (open) or permanently closed (destroy).

Each call to enter requires a corresponding call to exit, similar to the JVM implementation of the "synchronized" keyword that places a monitorenter op that the beginning of the synchronized portion and protects the synchronized portion with a try..finally construct that ensures the execution of a monitorexit op. For example, the following would ensure proper clean-up using a ThreadGate:

 gate.enter();
 try
     {
     ...
     }
 finally
     {
     gate.exit();
     }
 

Similarly, each call to close() should be matched with a call to open(), unless the gate is being destroyed:

 gate.close();
 try
     {
     ...
     }
 finally
     {
     gate.open();
     }
 

or:

 gate.close();
 gate.destroy();
 

The enter/exit calls can be nested; the same thread can invoke enter multiple times as long as exit is invoked a corresponding number of times. The close/open calls work in the same manner. Lastly, the thread that closes the gate may continue to enter/exit the gate even when it is closed since that thread has exclusive control of the gate.

Since:

Coherence 2.2

Author:

cp 2003.05.26; mf 2007.04.27

Nested Class Summary

static class

ThreadGate.ThreadLocalCounter Specialization of ThreadLocalObject that can be used for efficient thread local long counters.

Field Summary

static int	GATE_CLOSED GATE_CLOSED: A single thread is inside the gates; other threads cannot enter.
static int	GATE_CLOSING GATE_CLOSING: A thread is waiting to be the only thread inside the gates; other threads can only exit.
static int	GATE_DESTROYED GATE_DESTROYED: Life-cycle is complete; the object is no longer usable.
static int	GATE_OPEN GATE_OPEN: Threads may enter and exit the gates.

Constructor Summary

ThreadGate()
Default constructor.

Method Summary

boolean	close(long cMillis) Close the thread gate.
void	destroy() Destroy the thread gate.
protected long	doWait(long cMillis) Wait up to the specified number of milliseconds for notification.
boolean	enter(long cMillis) Enter the thread gate.
void	exit() Exit the gate.
int	getActiveCount() Return the number of unmatched completed enter calls.
int	getCloseCount() Return the number of unmatched completed close calls.
protected Thread	getClosingThread() Return the thread that is closing the gates.
int	getStatus() Return the current thread gate status.
protected long	getVersion() Return the total number of times the gate has been fully opened.
boolean	isActiveThread() Determine if the current thread has entered and not exited.
void	open() After the ThreadGate is closed by a call to close(), it can be re-opened by calling this method.
protected void	setCloseCount(int cClose) Specify the number of unmatched completed close calls.
protected void	setClosingThread(Thread thread) Specify the thread that is closing the gates.
protected void	setVersion(long cVersion) Specify the total number of times the gate has been fully opened.
String	toString() Provide a human-readable representation of this ThreadGate.
protected int	updateStatus(int nStatus) Update the current thread gate status, without changing the active count.

Field Detail

GATE_OPEN

public static final int GATE_OPEN

GATE_OPEN: Threads may enter and exit the gates.

See Also:

Constant Field Values

GATE_CLOSING

public static final int GATE_CLOSING

GATE_CLOSING: A thread is waiting to be the only thread inside the gates; other threads can only exit.

See Also:

Constant Field Values

GATE_CLOSED

public static final int GATE_CLOSED

GATE_CLOSED: A single thread is inside the gates; other threads cannot enter.

See Also:

Constant Field Values

GATE_DESTROYED

public static final int GATE_DESTROYED

GATE_DESTROYED: Life-cycle is complete; the object is no longer usable.

See Also:

Constant Field Values

Constructor Detail

ThreadGate

public ThreadGate()

Default constructor.

Method Detail

close

public boolean close(long cMillis)

Close the thread gate. A thread uses this method to obtain exclusive access to the resource represented by the thread gate. Each invocation of this method must ultimately have a corresponding invocation of the open method.

Parameters:

cMillis - maximum number of milliseconds to wait; pass -1 for forever or 0 for no wait

destroy

public void destroy()

Destroy the thread gate. This method can only be invoked if the gate is already closed.

enter

public boolean enter(long cMillis)

Enter the thread gate. A thread uses this method to obtain non-exclusive access to the resource represented by the thread gate. Each invocation of this method must ultimately have a corresponding invocation of the exit method.

Parameters:

cMillis - maximum number of milliseconds to wait; pass -1 for forever or 0 for no wait

exit

public void exit()

Exit the gate. A thread must invoke this method corresponding to each invocation of the enter method.

open

public void open()

After the ThreadGate is closed by a call to close(), it can be re-opened by calling this method. Only the thread that called close() can call open().

Throws:

IllegalStateException - if the gate is not closed or if open() is not called by the thread that called close()

doWait

protected long doWait(long cMillis)

Wait up to the specified number of milliseconds for notification. Caller must be synchronized.

getActiveCount

public int getActiveCount()

Return the number of unmatched completed enter calls.

isActiveThread

public boolean isActiveThread()

Determine if the current thread has entered and not exited. This is useful for detecting re-entrancy.

Returns:

true if the current thread has entered and not exited

Since:

Coherence 3.1

getVersion

protected long getVersion()

Return the total number of times the gate has been fully opened.

setVersion

protected void setVersion(long cVersion)

Specify the total number of times the gate has been fully opened.

The caller must have the gate closed.

getCloseCount

public int getCloseCount()

Return the number of unmatched completed close calls.

setCloseCount

protected void setCloseCount(int cClose)

Specify the number of unmatched completed close calls.

The caller must have the gate closed.

getClosingThread

protected Thread getClosingThread()

Return the thread that is closing the gates.

setClosingThread

protected void setClosingThread(Thread thread)

Specify the thread that is closing the gates.

The caller must be synchronized on the ThreadGate.

getStatus

public int getStatus()

Return the current thread gate status.

updateStatus

protected int updateStatus(int nStatus)

Update the current thread gate status, without changing the active count.

The caller must hold synchronization on the ThreadGate.

Parameters:

nStatus - the new status

Returns:

the old status

toString

public String toString()

Provide a human-readable representation of this ThreadGate.