Method and system for optimizing file table usage

• US 7,934,220 B2
• Filed: 03/17/2008
• Issued: 04/26/2011
• Est. Priority Date: 04/30/2003
• Status: Expired due to Fees

• Current Assignee: International Business Machines Corporation
• Original Assignee: International Business Machines Corporation
• Inventors: Xue, Xun, Pereyra, Hebert W., Kalmuk, David C., Lind, Jon A
• Primary Examiner(s): Nguyen; Van H
• Application Number:
  US12/049,991
• Publication Number:
  US 20080163243A1
• Time in Patent Office: 1,135 Days
• Field of Search: 719/310, 719/311, 719/312, 719/317, 709/202, 709/217, 709/219
• US Class Current: 719/317
• CPC Class Codes: G06F 9/544 Buffers; Shared memory; Pipes

Abstract

An operating system directed to using special properties of a common inter-process communications mechanism (IPC), namely UNIX domain socket-pairs or stream-pipes alternatively as a storage medium for file-descriptors of UNIX processes. When a file-descriptor is written into a socket-pair, and closed in the UNIX process, the file remains open, but occupies no space in the process'"'"' file-table. The file-descriptor may later be read out of the socket-pair to reestablish it in the file-table, and access it. This property is implemented in an IPC mechanism of UNIX operating system whereby a process such as a dispatcher may manage more connections and processes than its file-table size allow. This provides scalability improvements of the UNIX operating system.

Claims

1. A method for manipulating a file descriptor stored in a file table entry of a file table, the method comprising:

transferring, by a processing unit, the file descriptor stored in the file table entry of the file table from the file table entry to a shared socket pair to store the file descriptor in the shared socket pair, thereby preserving the file descriptor in the shared socket pair while permitting availability of the unloaded file table entry of the file table for other uses;

transferring, by the processing unit, the file descriptor stored in the shared socket pair from the shared socket pair to an available file table entry if access to the file descriptor stored in the shared socket pair is requested;

storing file descriptors which reference a first socket pair within a file table associated with a dispatcher process to reduce a number of file descriptors simultaneously stored within the file table associated with the dispatcher process, wherein the first socket pair stores a plurality of file descriptors associated with an agent process, and wherein each of the plurality of file descriptors references a corresponding closed file within a context of the agent process; and

transferring the file descriptors which reference the first socket pair to the agent process via an IPC mechanism.

2. The method of claim 1, further comprising:

receiving the file descriptors which reference the first socket pair from the agent process via the IPC mechanism, wherein the IPC mechanism comprises a second socket pair.

3. The method of claim 2, wherein the second socket pair comprises the shared socket pair.

4. The method of claim 3, further comprising:

obtaining the shared socket pair from a pool of shared socket pairs prior to a transfer of the file descriptors which reference the first socket pair to the agent process.

5. The method of claim 3, further comprising:

returning the shared socket pair to a pool of shared socket pairs following a receipt of the file descriptors which reference the first socket pair from the agent process.

6. The method of claim 1, further comprising:

partitioning the file table which maintains a plurality of file descriptors into a plurality of file table partitions of the file table, each of the plurality of file table partitions maintaining a subset of the plurality of file descriptors maintained in the file table;

reserving a file table partition within the plurality of file table partitions of the file table as a reserved file table partition to store a plurality of socket pair file descriptors, each of the plurality of socket pair file descriptors corresponding to one of a plurality of socket pairs, wherein each of the socket pairs is adapted to store an entire subset of file descriptors associated with a partition; and

storing file descriptors of a selected one of the plurality of file table partitions to one of the plurality of socket pairs using an associated one of the socket pair file descriptors, wherein storing the file descriptors of the selected one of the plurality of file table partitions to one of the plurality of socket pairs stores the associated socket pair file descriptors to the reserved file table partition.

7. The method of claim 6, further comprising:

storing to the selected one of the plurality of file table partitions the file descriptors from another socket pair in the plurality of socket pairs selected from the reserved file table partition, the another socket pair having stored file descriptors for a particular file table partition in the plurality of file table partitions.

8. The method of claim 7, further comprising:

choosing the another socket pair in response to a need to access a particular file descriptor stored by the another socket pair.

9. The method of claim 6, further comprising:

choosing the selected one of the plurality of file table partitions in response to a recent access to the selected one of the plurality of file table partitions.

10. A data processing system for manipulating a file descriptor stored in a file table entry of a file table, comprising:

a bus system;

a storage device connected to the bus system, wherein the storage device includes a set of instructions; and

a processing unit connected to the bus system, wherein the processing unit executes the set of instructions to;

transfer the file descriptor stored in the file table entry of the file table from the file table entry to a shared socket pair to store the file descriptor in the shared socket pair, thereby preserving the file descriptor in the shared socket pair while permitting availability of the unloaded file table entry of the file table for other uses;

transfer the file descriptor stored in the shared socket pair from the shared socket pair to an available file table entry if access to the file descriptor stored in the shared socket pair is requested;

store file descriptors which reference a first socket pair within a file table associated with a dispatcher process to reduce a number of file descriptors simultaneously stored within the file table associated with the dispatcher process, wherein the first socket pair stores a plurality of file descriptors associated with an agent process, and wherein each of the plurality of file descriptors references a corresponding closed file within a context of the agent process; and

transfer the file descriptors which reference the first socket pair to the agent process via an IPC mechanism.

11. A computer program product stored on a non-transitory computer readable medium having computer executable code embodied thereon for manipulating a file descriptor stored in a file table entry of a file table, the computer program product comprising:

code for transferring the file descriptor stored in the file table entry of the file table from the file table entry to a shared socket pair to store the file descriptor in the shared socket pair, thereby preserving the file descriptor in the shared socket pair while permitting availability of the unloaded file table entry of the file table for other uses;

code for transferring the file descriptor stored in the shared socket pair from the shared socket pair to an available file table entry if access to the file descriptor stored in the shared socket pair is requested;

code for storing file descriptors which reference a first socket pair within a file table associated with a dispatcher process to reduce a number of file descriptors simultaneously stored within the file table associated with the dispatcher process, wherein the first socket pair stores a plurality of file descriptors associated with an agent process, and wherein each of the plurality of file descriptors references a corresponding closed file within a context of the agent process; and

code for transferring the file descriptors which reference the first socket pair to the agent process via an IPC mechanism.

12. The computer program product of claim 11, further comprising:

code for receiving the file descriptors which reference the first socket pair from the agent process via the IPC mechanism, wherein the IPC mechanism comprises a second socket pair.

13. The computer program product of claim 12, wherein the second socket pair comprises the shared socket pair.

14. The computer program product of claim 13, further comprising:

code for obtaining the shared socket pair from a pool of shared socket pairs prior to a transfer of the file descriptors which reference the first socket pair to the agent process.

15. The computer program product of claim 13, further comprising:

code for returning the shared socket pair to a pool of shared socket pairs following a receipt of the file descriptors which reference the first socket pair from the agent process.

16. The computer program product of claim 11, further comprising:

code for partitioning the file table which maintains a plurality of file descriptors into a plurality of file table partitions of the file table, each of the plurality of file table partitions maintaining a subset of the plurality of file descriptors maintained in the file table;

code for reserving a file table partition within the plurality of file table partitions of the file table as a reserved file table partition to store a plurality of socket pair file descriptors, each of the plurality of socket pair file descriptors corresponding to one of a plurality of socket pairs, wherein each of the socket pairs is adapted to store an entire subset of file descriptors associated with a partition; and

code for storing file descriptors of a selected one of the plurality of file table partitions to one of the plurality of socket pairs using an associated one of the socket pair file descriptors, wherein storing the file descriptors of the selected one of the plurality of file table partitions to one of the plurality of socket pairs stores the associated socket pair file descriptors to the reserved file table partition.

17. The computer program product of claim 16, further comprising:

code for storing to the selected one of the plurality of file table partitions the file descriptors from another socket pair in the plurality of socket pairs selected from the reserved file table partition, the another socket pair having stored file descriptors for a particular file table partition in the plurality of file table partitions.

18. The computer program product of claim 17, further comprising:

code for choosing the another socket pair in response to a need to access a particular file descriptor stored by the another socket pair.