Method and system for robust futexes

• US 7,783,649 B2
• Filed: 02/01/2007
• Issued: 08/24/2010
• 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, Gleixner, Thomas, Drepper, Ulrich
• Primary Examiner(s): Ali; Mohammad
• Assistant Examiner(s): Hocker; John P
• Application Number:
  US11/670,095
• Publication Number:
  US 20080189282A1
• Time in Patent Office: 1,300 Days
• Field of Search: 707 1- 10, 707/104.1, 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 futex primitives, the method comprising:

Providing a private data structure in user-space, the private data structure being private to a first computer process and comprising at least one futex, wherein each futex serves as a lock on a resource provided by a computer system;

Registering the private data structure by the first computer process;

Linking a pending entry data structure to the private data structure;

Setting a pending entry flag in the pending entry data structure, wherein the pending entry flag indicates that the first computer process is about to acquire a selected futex;

Acquiring the selected futex from a plurality of futexes;

Linking the selected futex to the private data structure after acquiring the selected futex;

Detecting a termination of the first computer process;

Searching the private data structure and the pending entry data structure for a status of the selected futex, wherein at least one other computer process is waiting for the selected futex;

Setting a first flag for the selected futex indicating that the first computer process terminated prior to releasing the selected futex if the status indicates that the selected futex is held by the first computer process or if the pending entry flag is set;

Releasing the selected futex if the first flag is set for the selected futex; and

Notifying the at least one other computer process, and if the first flag is set for the selected futex, the at least one other computer process resolves race conditions and verifies a consistency of data associated with the resource locked by the selected futex.

2. The method of claim 1, further comprising:

waking a computer process of the at least one other computer process;

checking the first flag by the awakened computer process; and

processing the selected futex based on the first flag.

3. The method of claim 1, further comprising unlinking the selected futex from the private data structure.

4. The method of claim 1, wherein the selected futex is a free futex selected from the plurality of futexes.

5. The method of claim 4, further comprising setting a status of the selected futex as locked.

6. The method of claim 1, further comprising executing a function call to determine the location of the private data structure.

7. 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.

8. The method of claim 7, further comprising:

determining that the selected futex is being released; and

unlinking the selected futex from the private data structure.

9. A system for managing futex primitives, the system comprising:

a private data structure configured to store futexes designated as being held by a first computer process,

wherein the private data structure is registered by the first computer process and is private to the first computer process, and each of the futexes serves as a lock on a resource provided by a computer system;

a pending entry data structure configured to store a flag and linked to the private data structure, wherein the private and pending entry data structures are in user space; and

a futex module configured to;

set a pending entry flag in the pending entry data structure in response to the first computer process acquiring a selected robust futex from a plurality of robust futexes,

wherein the pending entry flag indicates that the first computer process is about to acquire the selected robust futex,

link the selected robust futex to the private data structure after the first computer process acquires the selected robust futex,

detect a termination of the first computer process,

search the private data structure and the pending entry data structure for a status of the selected robust futex, wherein at least one other computer process is waiting for the selected futex,

set a first flag indicating that the first computer process terminated prior to releasing the selected robust futex, if the selected robust futex is found in the private data structure or if the pending entry flag is set,

release the selected robust futex if the first flag is set for the selected robust futex, and

notify the at least one other computer process, and if the first flag is set for the selected robust futex, the at least one other computer process resolves race conditions and verifies a consistency of data associated with the resource locked by the selected robust futex.

10. The system of claim 9, wherein the futex module is further configured to reset the pending entry flag in the pending entry data structure after linking the selected robust futex to the private data structure.

11. The system of claim 10, wherein the futex module is further configured to determine that the selected robust futex is being released and unlink the selected robust futex from the private data structure.

12. The system of claim 9, wherein the futex module is further configured to wake a computer process of the at least one other computer process.