Method and system for robust futexes

• US 8,095,550 B2
• Filed: 08/23/2010
• Issued: 01/10/2012
• 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: Gleixner, Thomas, Drepper, Ulrich, Molnar, Ingo
• Primary Examiner(s): Ali, Mohammad
• Assistant Examiner(s): Hocker, John
• Application Number:
  US12/861,431
• Publication Number:
  US 20100318504A1
• Time in Patent Office: 505 Days
• Field of Search: 707/755, 707/756, 707/791
• US Class Current: 707/755
• 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:

selecting a free futex from a plurality of futexes in response to a request by the first computer process, wherein the first computer process acquires the futex;

registering a private data structure that is stored in user space,

wherein the private data structure tracks the futex that is held by a first computer process running in the user space,

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;

linking the futex held by the first computer process to the private data structure

detecting a termination of the first computer process that maintains the lock on the resource after termination;

searching the private data structure to identify the futex that is held by the first computer process that terminated; and

releasing the futex if the futex is identified as being held by the first computer process.

2. The method of claim 1, further comprising:

setting a flag for the futex; and

notifying a waiting computer process waiting for the futex, wherein the

waiting computer process determines that the flag is set and resolves race conditions associated with the resource locked by the futex.

3. The method of claim 1, further comprising:

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 free futex.

4. The method of claim 3, further comprising linking the pending entry data structure to the private data structure.

5. The method of claim 3, further comprising:

resetting the pending entry flag in the pending entry data structure after linking the futex held by the first computer process to the private data structure.

6. The method of claim 3, further comprising:

searching the pending data structure for the futex;

setting the flag if the futex is found in the private data structure or if the pending entry flag in the pending entry data structure is set; and

notifying a waiting computer process waiting for the futex, wherein the waiting computer process determines that the flag is set and resolves race conditions associated with the resource locked by the futex.

7. The method of claim 1, wherein registering a private data structure further comprises:

receiving a system call from the first computer process to register the private data structure with a kernel; and

executing a function call to the kernel to determine whether the private data structure has been registered.

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

9. The method of claim 2, wherein notifying a waiting computer process further comprises waking the waiting computer process.

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

a private data structure stored in user space, the private data structure being configured to track a futex that is held by a first computer process running in the user space,

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;

select a free futex from a plurality of futexes in response to a request by the first computer process, wherein the first computer process acquires the futex;

link the futex held by the first computer process to the private data structure

register the private data structure;

detect a termination of the first computer process that maintains the lock on the resource after termination;

search the private data structure to identify the futex that is held by the first computer process that terminated; and

release the futex if the futex is identified as being held by the first computer process.

11. The apparatus of claim 10, wherein the futex module is further configured to set a flag for the futex and notify a waiting computer process waiting for the futex, wherein the waiting computer process determines that the flag is set and resolves race conditions associated with the resource locked by the futex.

12. The apparatus of claim 10, 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 free 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 futex to the private data structure.

13. The apparatus of claim 12, wherein the futex module is further configured to:

search the pending entry data structure for the futex;

set a flag if the futex is found in the private data structure or if the pending entry flag in the pending entry data structure is set; and

notify a waiting computer process waiting for the futex, wherein the waiting computer process determines that the flag is set and resolves race conditions associated with the resource locked by the futex.

14. A system for managing primitives, comprising:

a memory configured to store a private data structure in user space, the private data structure being configured to track a futex that is held by a first computer process running in the user space, 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 processor coupled to the memory and configured to;

select a free futex from a plurality of futexes in response to a request by the first computer process, wherein the first computer process acquires the free futex;

register the private data structure;

link the futex held by the first computer process to the private data structure;

detect a termination of the first computer process that maintains the lock on the resource after termination;

search the private data structure in the memory to identify the futex that is held by the first computer process that terminated; and

release the futex if the futex is identified as being held by the first computer process.

15. The system of claim 14, wherein the processor is further configured to:

set a flag for the futex;

notify a waiting computer process waiting for the futex, wherein the waiting computer process determines that the flag is set and resolves race conditions associated with the resource locked by the selected futex.

16. The system of claim 14, 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 free 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 futex to the private data structure.

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

search the pending entry data structure for the futex; and

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