Lock (Jikes RVM API)

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

Field Summary

Fields
Modifier and Type	Field and Description
`private static int`	`CLEAR` Lock is not held and the queue is empty.
`private static int`	`CLEAR_QUEUED` Lock is not held but the queue is non-empty.
`private int`	`id`
`private static int`	`lockCount`
`private static int`	`LOCKED` Lock is held and the queue is empty.
`private static int`	`LOCKED_QUEUED` Lock is held and the queue is non-empty.
`private String`	`name`
`private ThreadQueue`	`queue`
`private static 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.
`private static int`	`SPIN_LIMIT`
`private int`	`state`
`private RVMThread`	`thread`
`private int`	`where`

Constructor Summary

Constructors
Constructor and Description

Lock()

Lock(String name)

Constructors
Constructor and Description
`Lock()`
`Lock(String name)`

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`void`	`acquire()` Try to acquire a lock and spin-wait until acquired.
`void`	`check(int w)` Perform sanity checks on the lock.
`void`	`release()` Release the lock by incrementing serving counter.
`void`	`setName(String str)` Set the name of this lock instance

Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- Field Detail
  - 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.
    
    See Also:
    
    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 final ThreadQueue queue
```
  - state
```
private int state
```
  - thread
```
private RVMThread thread
```
  - where
```
private int where
```
- Constructor Detail
  - Lock
```
public Lock(String name)
```
  - Lock
```
public Lock()
```
- Method Detail
  - 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

Class Lock

Field Summary

Constructor Summary

Method Summary

Methods inherited from class java.lang.Object

Field Detail

name

id

lockCount

SPIN_LIMIT

CLEAR

LOCKED

CLEAR_QUEUED

LOCKED_QUEUED

QUEUEING

queue

state

thread

where

Constructor Detail

Lock

Lock

Method Detail

setName

acquire

check

release