METHOD AND SYSTEM FOR ROBUST FUTEXES

• US 20100318504A1
• Filed: 08/23/2010
• Published: 12/16/2010
• Est. Priority Date: 02/01/2007
• Status: Active Grant

• Current Assignee: Red Hat, Inc. (International Business Machines Corporation)
• Original Assignee: Red Hat, Inc. (International Business Machines Corporation)
• Inventors: Molnar, Ingo, Drepper, Ulrich, Gleixner, Thomas
• Granted Patent: US 8,095,550 B2
• Time in Patent Office: Days
• US Class Current: 707/704
• CPC Class Codes: G06F 16/2343 Locking methods, e.g. distributed locking or locking implementation details
• CPC Class Codes: G06F 9/526 Mutual exclusion algorithms

Abstract

An embodiment relates to a method of managing primitives. The method includes providing a data structure available in user-space where the data structure comprises at least one futex. The method also includes detecting a termination of the process and searching the data structure for status of the at least one futex. The method further includes releasing the at least one futex in response to status of the at least one futex being held and setting a flag for at least one futex. The method further includes notifying at least one process waiting for the released at least one futex.

Claims

1. A method of managing primitives, the method comprising:

providing a private data structure in user space, the private data structure being configured to link to a futex designated as being held by a first computer process, wherein the private data structure is private to the first computer process and wherein the futex serves as a lock on a resource provided by a computer system;

detecting a termination of the first computer process;

searching the private data structure for a status of the futex;

releasing the futex if the status indicates that the futex is held by the first computer process; and

setting a first flag for the futex indicating that the first computer process terminated prior to releasing the futex.

2. The method of claim 1, further comprising:

notifying a waiting computer process waiting for the selected futex;

determining by the waiting computer process that the first flag is set; and

verifying a consistency of data associated with the resource locked by the selected futex.

3. The method of claim 1, further comprising:

selecting a free futex from a plurality of futexes in response to a request by the first computer process, the selected futex being acquired by the first computer process;

linking the selected futex to the private data structure; and

setting a status of the selected futex as locked.

4. The method of claim 3, wherein acquiring the selected futex further comprises:

providing a pending entry data structure; and

setting a pending entry flag in the pending entry data structure indicating that the first computer process is about to acquire the selected futex.

5. The method of claim 4, further comprising linking the pending entry data structure to the private data structure.

6. The method of claim 4, further comprising:

resetting the pending entry flag in the pending entry data structure after linking the selected futex to the private data structure.

7. The method of claim 4, wherein setting a first flag for the selected futex further comprises:

searching the pending data structure for the selected futex; and

setting the first flag if the selected futex is found in the private data structure or if the pending entry flag in the pending entry data structure is set.

8. The method of claim 1, further comprising:

registering by the first computer process the private data structure with a kernel; and

executing a function call to the kernel to determine the location of the private data structure.

9. The method of claim 1, wherein releasing the selected futex further comprises unlinking the futex from the private data structure.

10. The method of claim 1, wherein notifying a waiting computer process further comprises waking the waiting computer process.

11. An apparatus for managing primitives in a computer system, the apparatus comprising:

a private data structure in user space, the private data structure being configured to link to a futex designated as being held by a first computer process, wherein the private data structure is private to the first computer process and wherein the futex serves as a lock on a resource provided by a computer system; and

a futex module configured to—

detect a termination of the first computer process;

search the private data structure for a status of the futex;

release the futex if the status indicates that the futex is held by the first computer process; and

set a first flag for the futex indicating that the first computer process terminated prior to releasing the futex.

12. The apparatus of claim 11, wherein the futex module is further configured to notify a waiting computer process waiting for the futex, and wherein the waiting computer process determines that the first flag is set and verifies a consistency of data associated with the resource locked by the futex.

13. The apparatus of claim 11, wherein the futex module is further configured to:

select a free futex from a plurality of futexes in response to a request by the first computer process, the selected futex being acquired by the first computer process;

link the selected futex to the private data structure; and

set a status of the selected futex as locked.

14. The apparatus of claim 13, wherein the futex module is further configured to:

provide a pending entry data structure;

set a pending entry flag in the pending entry data structure indicating that the first computer process is about to acquire the selected futex;

link the pending entry data structure to the private data structure; and

reset the pending entry flag in the pending entry data structure after linking the selected futex to the private data structure.

15. The apparatus of claim 14, wherein the futex module is further configured to:

search the pending entry data structure for the selected futex; and

set the first flag if the selected futex is found in the private data structure or if the pending entry flag in the pending entry data structure is set.

16. A system for managing primitives, comprising:

a memory configured to store a private data structure in user space, the private data structure linking to a futex designated as being held by a first computer process, wherein the private data structure is private to the first computer process and wherein the futex serves as a lock on a resource provided by a computer system;

a processor coupled to the memory and configured to—

detect a termination of the first computer process;

search the private data structure in the memory for a status of the futex;

release the futex if the status indicates that the futex is held by the first computer process; and

set a first flag for the futex indicating that the first computer process terminated prior to releasing the futex.

17. The system of claim 16, wherein the processor is further configured to:

notify a waiting computer process waiting for the futex;

determine that the first flag is set in response to a request by the waiting computer process; and

verify a consistency of data associated with the resource locked by the selected futex.

18. The system of claim 16, wherein the processor is further configured to:

select a free futex from a plurality of futexes in response to a request by the first computer process, the selected futex being acquired by the first computer process;

link the selected futex to the private data structure; and

set a status of the selected futex as locked.

19. The system of claim 18, wherein the processor is further configured to:

provide a pending entry data structure;

set a pending entry flag in the pending entry data structure indicating that the first computer process is about to acquire the selected futex;

link the pending entry data structure to the private data structure; and

reset the pending entry flag in the pending entry data structure after linking the selected futex to the private data structure.

20. The system of claim 19, wherein the processor is further configured to:

search the pending entry data structure for the selected futex; and

set the first flag if the selected futex is found in the private data structure or if the pending entry flag in the pending entry data structure is set.