org.jikesrvm.mm.mmtk
Class Lock

java.lang.Object
  org.mmtk.vm.Lock
      org.jikesrvm.mm.mmtk.Lock

public class Lock
extends Lock

Adaptive mutex with a spinlock fast path. Designed for good performance on native threaded systems. This implementation has the following specific properties:

• It behaves like a spinlock on the fast path (one CAS to lock, one CAS to unlock, if there is no contention).
• It has the ability to spin for some predetermined number of cycles (see SPIN_LIMIT).
• Adapts to contention by eventually placing contending threads on a queue and parking them.
• Has a weak fairness guarantee: contenders follow queue discipline, except that new contenders may "beat" the thread at the head of the queue if they arrive just as the lock becomes available and the thread at the head of the queue just got scheduled.

Author:

Filip Pizlo

name

private String name

id

private final int id

lockCount

private static int lockCount

SPIN_LIMIT

private static final int SPIN_LIMIT

See Also:

Constant Field Values

CLEAR

private static final int CLEAR

Lock is not held and the queue is empty. When the lock is in this state, there may be a thread that just got dequeued and is about to enter into contention on the lock.

See Also:

Constant Field Values

LOCKED

private static final int LOCKED

Lock is held and the queue is empty.

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Constant Field Values

CLEAR_QUEUED

private static final int CLEAR_QUEUED

Lock is not held but the queue is non-empty. This state guarantees that there is a thread that got dequeued and is about to contend on the lock.

See Also:

Constant Field Values

LOCKED_QUEUED

private static final int LOCKED_QUEUED

Lock is held and the queue is non-empty.

See Also:

Constant Field Values

QUEUEING

private static final int QUEUEING

Some thread is currently engaged in an enqueue or dequeue operation, and will return the lock to whatever it was in previously once that operation is done. During this states any lock/unlock attempts will spin until the lock reverts to some other state.

See Also:

Constant Field Values

queue

private ThreadQueue queue

state

private int state

thread

private RVMThread thread

where

private int where

Lock

public Lock(String name)

Lock

public Lock()

setName

public void setName(String str)

Description copied from class: Lock

Set the name of this lock instance

Specified by:

setName in class Lock

Parameters:

str - The name of the lock (for error output).

acquire

public void acquire()

Description copied from class: Lock

Try to acquire a lock and spin-wait until acquired.

Specified by:

acquire in class Lock

check

public void check(int w)

Description copied from class: Lock

Perform sanity checks on the lock. For debugging.

Specified by:

check in class Lock

Parameters:

w - Identifies the code location in the debugging output.

release

public void release()

Description copied from class: Lock

Release the lock by incrementing serving counter.

Specified by:

release in class Lock