edu.wpi.first.wpilibj.communication
Class Semaphore

java.lang.Object
  edu.wpi.first.wpilibj.communication.Semaphore

public class Semaphore
extends java.lang.Object

Emulates various VXWorks semaphores using Java native methods. Note: The options passed in currently are completely ignored.

Author:

wolf

Todo:

do something with the options?

Nested Class Summary

static class

Semaphore.Options Options to create a semaphore with.

Field Summary

static int

WAIT_FOREVER

Constructor Summary

Semaphore(Semaphore.Options options)
Create a new mutex semaphore.

Semaphore(Semaphore.Options options, boolean initialState)
Create a boolean semaphore with the given initial state.

Semaphore(Semaphore.Options options, int count)
Create a counting semaphore with the given number of permits.

Method Summary

void	close()
protected void	doWaitForever() Attempt to wait forever on the semaphore.
protected void	doWaitMillis(int timeout) Attempt to wait for a certain number of milliseconds on a semaphore.
void	flush() Unblock every task that is blocked by the semaphore.
void	free() Free all of the resources associated with this semaphore.
Pointer	getPointer()
void	give() Release the semaphore.
void	takeForever() Take the semaphore.
void	takeMillis(int timeout) Take the semaphore.
boolean	tryTake() Attempt to take the semaphore, but don't block.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

WAIT_FOREVER

public static final int WAIT_FOREVER

See Also:

Constant Field Values

Constructor Detail

Semaphore

public Semaphore(Semaphore.Options options)

Create a new mutex semaphore.

Parameters:

options - The options to create the semaphore with.

Semaphore

public Semaphore(Semaphore.Options options,
                 boolean initialState)

Create a boolean semaphore with the given initial state.

Parameters:

options - The options to create the semaphore with.

initialState - The initial state for the semaphore to have.

Semaphore

public Semaphore(Semaphore.Options options,
                 int count)

Create a counting semaphore with the given number of permits.

Parameters:

options - The options to create the semaphore with.

count - The initial count for the semaphore to hold.

Method Detail

flush

public void flush()
           throws SemaphoreException

Unblock every task that is blocked by the semaphore.

Throws:

SemaphoreException

give

public void give()
          throws SemaphoreException

Release the semaphore.

Throws:

SemaphoreException

tryTake

public boolean tryTake()
                throws SemaphoreException

Attempt to take the semaphore, but don't block.

Returns:

True if the semaphore was successfully taken, false otherwise

Throws:

SemaphoreException

doWaitForever

protected void doWaitForever()
                      throws SemaphoreException,
                             java.lang.InterruptedException

Attempt to wait forever on the semaphore. Called in a loop by takeMillis() to catch InterruptedExceptions.

Throws:

SemaphoreException

java.lang.InterruptedException

doWaitMillis

protected void doWaitMillis(int timeout)
                     throws SemaphoreException,
                            java.lang.InterruptedException

Attempt to wait for a certain number of milliseconds on a semaphore. Called in a loop by takeMillis() to catch InterruptedExceptions.

Parameters:

timeout - The number of milliseconds to wait, at most.

Throws:

SemaphoreException

java.lang.InterruptedException

getPointer

public final Pointer getPointer()

takeMillis

public final void takeMillis(int timeout)
                      throws SemaphoreException

Take the semaphore. Block for timeout milliseconds.

Parameters:

timeout - The number of milliseconds to block.

Throws:

SemaphoreException - if the lock can't be take in timeout seconds

takeForever

public final void takeForever()
                       throws SemaphoreException

Take the semaphore. Block forever until semaphore is available.

Throws:

SemaphoreException

close

public final void close()
                 throws SemaphoreException

Throws:

SemaphoreException

free

public final void free()
                throws SemaphoreException

Free all of the resources associated with this semaphore. Actually does nothing; this is for VxWorks semaphores.

Throws:

SemaphoreException