Method and system for using the event wait list anchor as a lock for events

• US 5,961,583 A
• Filed: 11/22/1996
• Issued: 10/05/1999
• Est. Priority Date: 11/22/1996
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Van Fleet, James William
• Primary Examiner(s): Banankhah, Majid A.
• Application Number:
  US08/755,274
• Time in Patent Office: 1,047 Days
• Field of Search: 395/670, 395/672, 395/673, 395/674, 709/100, 709/102, 709/103, 709/104
• US Class Current: 718/102
• CPC Class Codes: G06F 9/52 Program synchronisation; Mutual exclusion, e.g. by means of semaphores

Abstract

A method and apparatus for maintaining a list for threads which are awaiting their occurrence of event. First a thread is detected that desires to perform some type of action based upon the occurrence of an event. Thereafter, the value of an event list anchor is set to indicate that it is currently unavailable. Thereafter, the value of the event list anchor set equal to the identification of the second thread.

Claims

1. A method of managing threads in a data processing system, comprising:

detecting that a first thread desires to perform some type of action, based upon the occurrence of an event;

locking an event list by setting an event list anchor equal to a first value, wherein the event list anchor is a head of the event list, and wherein the first value indicates that the event list is currently locked; and

setting the event list anchor equal to an identification of the first thread, wherein said setting the event list anchor equal to the identification of the first thread causes the event list to be unlocked.

2. A method of managing threads according to claim 1, further comprising:

upon the occurrence of the event, locking the event list by setting the event list anchor equal to the first value;

making the first thread executable; and

setting the event list anchor equal to a second value, wherein the second value indicates that the event list is empty.

3. A method of managing threads according to claim 1, further comprising:

detecting that a second thread desires to perform some type of action based upon the occurrence of the event;

locking the event list by setting the event list anchor equal to the first value;

adding the second thread to the event list; and

setting the event list anchor equal to the identification of the first thread.

4. A method of managing threads according to claim 3, wherein said adding comprises setting a pointer associated with the first thread equal to an identification of the second thread.

5. A method of managing threads according to claim 3, further comprising:

detecting that a third thread desires to perform some type of action based upon the occurrence of the event;

detecting that the event list anchor is equal to the first value;

waiting until the event list anchor is not equal to the first value;

upon detecting that the event list anchor is not equal to the first value, performing the following;

locking the event list by setting the event list

anchor equal to the first value;

adding the third thread to the event list; and

setting the event list anchor equal to the

identification of the first thread.

6. A method of managing threads according to claim 3, further comprising:

upon the occurrence of the event, locking the event list by setting the event list anchor equal to the first value;

making each thread in the event list executable; and

setting the event list anchor equal to a second value, wherein the second value indicates that the event list is empty.

7. A method of managing threads according to claim 3, further comprising:

upon the occurrence of the event, locking the event list by setting the event list anchor equal to the first value;

determining a highest priority thread in the event list; and

making the highest priority thread executable.

8. A method of managing threads according to claim 7, further comprising:

if the highest priority thread in the event list is the first thread in the list, setting the event list anchor equal to the identification of the second thread.

9. A data processing system, comprising:

means for detecting that a first thread desires to perform some type of action, based upon the occurrence of an event;

means for locking an event list by setting an event list anchor equal to a first value, wherein the event list anchor is a head of the event list, and wherein the first value indicates that the event list is currently locked; and

means for unlocking the event list by setting the event list anchor equal to an identification of the first thread.

10. A data processing system according to claim 9, further comprising:

means for making the first thread executable; and

means for setting the event list anchor equal to a second value, wherein the second value indicates that the event list is empty.

11. A data processing system according to claim 9, further comprising:

means for detecting that a second thread desires to perform some type of action based upon the occurrence of the event;

means for locking the event list, upon detecting that the second thread desires to perform some type of action, by setting the event list anchor equal to the first value;

means for adding the second thread to the event list; and

means for setting the event list anchor equal to the identification of the first thread after the second thread has been added to the event list.

12. A data processing system according to claim 11, further comprising:

means for detecting that a third thread desires to perform some type of action based upon the occurrence of the event;

means for detecting that the event list anchor is equal to the first value;

means for waiting until the event list anchor is not equal to the first value;

means for locking the event list, upon detecting that the event list anchor is not equal to the first value, by setting the event list anchor equal to the first value;

means for adding the third thread to the event list; and

means for setting the event list anchor equal to the identification of the first thread after the third thread has been added to the event list.

13. A data processing system according to claim 11, further comprising:

means for locking the event list upon the occurrence of the event, by setting the event list anchor equal to the first value;

means for making each thread in the event list executable; and

means for setting the event list anchor equal to a second value, wherein the second value indicates that the event list is empty.

14. A data processing system according to claim 11, further comprising:

means for locking the event list upon the occurrence of the event, by setting the event list anchor equal to the first value; and

means for making a selected thread in the event list executable.

15. A computer program product on a computer usable medium, the computer usable medium having computer usable program means embodied therein, the computer usable program means comprising:

means for detecting that a first thread desires to perform some type of action, based upon the occurrence of an event;

means for locking an event list by setting an event list anchor equal to a first value, wherein the event list anchor is a head of the event list, and wherein the first value indicates that the event list is currently locked; and

means for unlocking the event list by setting the event list anchor equal to an identification of the first thread.

16. A computer program product according to claim 15, wherein the computer usable program means further comprises:

means for making the first thread executable; and

means for setting the event list anchor equal to a second value, wherein the second value indicates that the event list is empty.

17. A computer program product according to claim 15, wherein the computer usable program means further comprises:

means for detecting that a second thread desires to perform some type of action based upon the occurrence of the event;

means for locking the event list, upon detecting that the second thread desires to perform some type of action, by setting the event list anchor equal to the first value;

means for adding the second thread to the event list; and

means for setting the event list anchor equal to the identification of the first thread after the second thread has been added to the event list.

18. A computer program product according to claim 17, wherein the computer usable program means further comprises:

means for detecting that a third thread desires to perform some type of action based upon the occurrence of the event;

means for detecting that the event list anchor is equal to the first value;

means for waiting until the event list anchor is not equal to the first value;

means for locking the event list, upon detecting that the event list anchor is not equal to the first value, by setting the event list anchor equal to the first value;

means for adding the third thread to the event list; and

means for setting the event list anchor equal to the identification of the first thread after the third thread has been added to the event list.

19. A computer program product according to claim 17, wherein the computer usable program means further comprises:

means for locking the event list upon the occurrence of the event, by setting the event list anchor equal to the first value;

means for making each thread in the event list executable; and

means for setting the event list anchor equal to a second value, wherein the second value indicates that the event list is empty.

20. A computer program product according to claim 16, further comprising:

means for locking the event list upon the occurrence of the event, by setting the event list anchor equal to the first value; and

means for making a selected thread in the event list executable.