Event-based synchronization

• US 7,117,496 B1
• Filed: 05/09/2001
• Issued: 10/03/2006
• Est. Priority Date: 05/09/2001
• Status: Active Grant

• Current Assignee: Teradata US, Inc. (Teradata Corporation)
• Original Assignee: NCR Corporation
• Inventors: Mahata, Debashis, Sharma, Srikant S., Ramesh, Bhashyam
• Primary Examiner(s): Thomson, William
• Assistant Examiner(s): CAO, DIEM K
• Application Number:
  US09/851,592
• Time in Patent Office: 1,973 Days
• Field of Search: 718100-108, 719310-316, 719318-320, 719/328
• US Class Current: 718/102
• CPC Class Codes: G06F 9/52 Program synchronisation; Mutual exclusion, e.g. by means of semaphores
• CPC Class Codes: G06F 9/522 Barrier synchronisation
• CPC Class Codes: G06F 9/542 Event management; Broadcasting; Multicasting; Notifications

Abstract

A synchronization method and apparatus defines event objects to enable synchronization of execution entities (e.g., threads). In one arrangement, the synchronization method and apparatus is used in conjunction with a Unix operating system. By defining event objects on which threads or other execution entities can wait upon, multiple threads can wait on one event, or alternatively, one thread can wait on multiple events. Furthermore, using the event-based synchronization method and apparatus, it is possible to specify behavior, particularly when one thread or other execution entity waits on multiple events. For example, the behavior specified can be that a condition is satisfied if any of the events occur, if all of the events occur, or some other logical combination of events occur.

Claims

1. A system comprising:

a Unix operating system;

a plurality of execution entities, the plurality of execution entities including a first execution entity;

an event control module adapted to create event objects representing respective events each having a state, the first execution entity to wait on plural events;

a data structure associated with the first execution entity, the data structure containing information of the plural events that the first execution entity is waiting on, the data structure further containing an indicator settable to one of plural values to specify respective plural logical relationships between the plural events; and

a controller adapted to awaken the first execution entity by signaling the first execution entity in response to one or more event state changes of the states of the plural events according to the logical relationship specified by the indicator,

wherein each event object contains an indication of the state of the event, wherein the indication has a first state to indicate that the corresponding event has been signaled and a second state to indicate that the corresponding event has not been signaled,

wherein each event object has a type indication to indicate whether the event object state indication is to be automatically reset to the second state from the first state once the event has been signaled or to be manually reset to the second state from the first state by an explicit action,

wherein if a particular one of the event objects is to be automatically reset, then only one of plural execution entities waiting on the particular event object will be awakened in response to the corresponding event being signaled, and

wherein if the particular event object is to be manually reset, then all execution entities waiting on the particular event object will be awakened in response to the corresponding event being signaled.

2. The system of claim 1, wherein the event control module is adapted to define a queue for a first one of the event objects, the queue having plural entries corresponding to plural execution entities waiting on the event represented by the first event object.

3. The system of claim 2, wherein the event control module is adapted to further create second objects, wherein each entry of the queue comprises a link to a corresponding second object, each execution entity to sleep on an associated second object to wait on the event represented by the first event object.

4. The system of claim 3, wherein each second object is defined by a condition variable.

5. The system of claim 4, wherein the controller signals each thread by signaling the condition variable.

6. The system of claim 3, wherein each second object is defined by a condition variable and a mutex.

7. The system of claim 1, further comprising queues associated with corresponding event objects representing events the first execution entity is waiting on, each queue containing an entry corresponding to the first execution entity.

8. The system of claim 7, wherein the event control module is adapted to define a barrier object, the first execution entity to sleep on the barrier object to wait on the plural events, the queue of each event object containing a link to the barrier object.

9. The system of claim 8, wherein the barrier object is defined at least by a condition variable.

10. The system of claim 8, wherein the barrier object is defined at least by a condition variable and a mutex.

11. The system of claim 1, wherein the event control module comprises a library.

12. The system of claim 1, wherein the execution entities comprise threads.

13. The system of claim 12, further comprising plural processes, each process associated with one or more threads,

the event control module to create a local event to synchronize threads within a process and to create a global event to synchronize threads of different processes.

14. The system of claim 13, wherein the global event comprises a named event.

15. The system of claim 1, further comprising a plurality of nodes, each node comprising one or more of the plurality of execution entities.

16. The system of claim 1, wherein the indicator is settable to a first value to specify a logical AND relationship between the plural events, and in response to the first value of the indicator, the controller to awaken the first execution entity in response to all of the plural events waited on by the first execution entity being signaled.

17. The system of claim 16, wherein the indicator is settable to a second value to specify a logical OR relationship between the plural events, and in response to the second value of the indicator, the controller to awaken the first execution entity in response to any of the plural events waited on by the first execution entity being signaled.

18. An article comprising at least one storage medium containing instructions for providing event-based synchronization in a system in which execution entities are running, the instructions when executed causing the system to:

generate event objects in a Unix operating system environment representing events used for synchronizing execution entities in the system, each event object having a state to indicate if the corresponding event has been signaled;

provide a queue containing entries associated with a first event object, each entry associated with a corresponding execution entity, the plural entries of the queue enabling plural execution entities to wait on the first event object; and

selectively set a type variable to one of a first value and a second value, the first value indicating that the first event object is of an auto-reset type, and the second value indicating that the first event object is of a manual reset type;

in response to the state of the first event object indicating the corresponding event has been signaled,

automatically clear the state of the first event object to an un-signaled state and awaken only one of the plural execution entities waiting on the first event object in response to the type variable being set to the first value, and

not clear the state of the first event object until manually cleared and awaken all threads waiting on the first event object in response to the type variable being set to the second value.

19. The article of claim 18, wherein the instructions when executed cause the system to further create barrier objects, each execution entity waiting on a corresponding barrier object to wait on an event.

20. The article of claim 19, wherein the instructions when executed cause the system to create barrier objects by defining each barrier object based on a condition variable according to the Unix operating system.

21. The article of claim 19, wherein the instructions when executed cause the system to create barrier objects by defining each barrier object based on a condition variable and mutex according to the Unix operating system.

22. The article of claim 19, wherein the queue of the first event object contains entries pointing to the barrier objects of the plural execution entities waiting on the first event object.

23. The article of claim 22, wherein the instructions when executed cause the system to provide a routine associated with each event object, the routine of the first event object to traverse the queue of the first event object and to signal the barrier objects pointed to by the entries in the queue of the first event object.

24. The article of claim 18, wherein a first one of the execution entities waits on plural events represented by respective event objects, the instructions when executed causing the system to:

provide a data structure containing information of the plural events waited upon by the first execution entity, the data structure further containing an indicator settable to one of plural values to specify respective plural logical relationships between the plural events waited on by the first execution entity; and

awaken the first execution entity in response to states of the plural events waited upon by the first execution entity according to the logical relationship specified by the indicator.

25. The article of claim 24, wherein the instructions when executed cause the system to set the indicator to a value to indicate a logical AND relationship, wherein awakening the first execution entity is in response to all of the plural events waited upon by the first execution entity being signaled.