Method and apparatus for user level monitor implementation

• US 6,473,820 B1
• Filed: 12/02/1999
• Issued: 10/29/2002
• Est. Priority Date: 12/08/1998
• Status: Expired due to Term

• Current Assignee: Oracle America, Inc. (Oracle Corporation)
• Original Assignee: Sun Microsystems Incorporated (Oracle Corporation)
• Inventors: Zhang, Hong
• Primary Examiner(s): THAI, XUAN MARIAN
• Application Number:
  US09/454,234
• Time in Patent Office: 1,062 Days
• Field of Search: 710/200, 710/240, 710/52, 709/1, 709/100, 709/106, 709/107, 709/102, 712/220, 712/245
• US Class Current: 710/240
• CPC Class Codes: G06F 9/526 Mutual exclusion algorithms

Abstract

Methods and apparatus for implementing an atomic monitor wait operation are disclosed. According to one aspect of the present invention, a computer-implemented method for implementing an atomic monitor wait operation includes creating a semaphore specific to a first thread. The semaphore is then placed in a wait queue associated with an object whose object lock is owned by the first thread in order to, in one implementation, preserve queue order. The first thread then exits a monitor associated with the object by, in one embodiment, releasing the object lock. The first thread then suspends execution until the semaphore receives notification that the object lock is available.

Claims

1. A computer-implemented method for implementing an atomic monitor wait operation, comprising:

creating a semaphore specific to a first thread desiring to exit a monitor associated with a target object having an object lock;

placing the semaphore in a wait queue associated with the target object; and

releasing the object lock by the first thread thereby allowing a second thread to execute a synchronous operation on the target object.

2. A method as recited in claim 1, further including:

suspending execution by the first thread;

receiving a notify call by the semaphore when the object lock is available; and

reacquiring the object lock by the first thread.

3. A method as recited in claim 2, wherein the receiving further includes determining if a period of time allocated for a timeout condition has elapsed.

4. A method as recited in claim 3, wherein when it is determined that the timeout period has not elapsed then the first thread executes a synchronous operation on the target object.

5. A method as recited in claim 4, further including removing the semaphore from the wait queue.

6. A computer program product for implementing an atomic monitor wait operation, comprising:

computer code that creates a semaphore specific to a first thread desiring to exit a monitor associated with a target object have an object lock;

computer code that places the semaphore in a wait queue associated with the target object;

computer code that releases the object lock by the first thread thereby allowing a second thread to execute a synchronous operation on the target object; and

a computer readable medium that stores the computer codes.

7. A computer program product according to claim 6 wherein the computer readable medium is a data signal embodied in a carrier wave.

8. A computer program product according to claim 6 further including computer code that suspends execution by the first thread;

computer code that receives a notify call by the semaphore when the object lock is available; and

computer code that re-acquires the object lock by the first thread.

9. A computer system including a memory which includes a plurality of threads, each of the plurality of threads, the computer system comprising:

a processor coupled to the memory; and

an object including an object header and an associate wait queue, the object header being arranged to contain a monitor which includes information relating to the ownership of object,

a first thread selected from the plurality of threads that has locked the object; and

a semaphore created by and specific to the first thread;

the first thread places the semaphore into the wait queue prior to releasing an object lock in furtherance of an atomic monitor wait operation.

10. A computer system as recited in claim 9 further including a second thread selected from the plurality of threads, the second thread being arranged to acquire the object lock after it has been released by the first thread in order to execute synchronous operations on the object.

11. A computer system as recited in claim 10 wherein the first thread suspends execution;

receiving a notify call by the semaphore when the object lock is available; and

re-acquiring the object lock by the first thread.

12. A computer system as recited in claim 11, wherein when the first thread suspends execution such that when the object lock is made available, the second thread receives a notify call that was generated by the first thread.

13. A computer system as recited in claim 12, wherein when the second thread receives the notify call, a determination is made if a period of time allocated for a timeout condition has elapsed.

14. A computer system as recited in claim 13, wherein when it is determined that the timeout period has not elapsed then the first thread re-acquires the object lock.

15. A computer system as recited in claim 14, wherein the semaphore is then removed from the wait queue.

16. A computer system as recited in claim 15, wherein the first thread executes a synchronous operation on the target object.