Data processing system with memory access
A data processing system with memory access comprising an operating system for supporting processes, such that the process are associated with one or more resources and the operating system being arranged to police the accessing by processes of resources so as to inhibit a process from accessing resources with which it is not associated. Part of this system is an interface for interfacing between each process and the operating system and a memory for storing state information for at least one process. The interface may be arranged to analyze instructions from the processes to the operating system, and upon detecting an instruction to re-initialize a process cause state information corresponding to that pre-existing state information to be stored in the memory as state information for the re-initialized process and to be associated with the resource.
1. A data processing system arranged to control access by a plurality of processes to a region of shared memory, the data processing system being arranged to:
prevent more than one of the plurality of processes from concurrently accessing the region of shared memory by locking the region of shared memory;
establish a data structure for holding items of a first type each of the items configured to store a process identifier configured to identify a particular process that has attempted and failed to access the region of shared memory operation to be performed by the particular process on the region of shared memory;
store a first process identifier for the first process that has attempted and failed to access the region of shared memory, and a first operation intended to be performed by the first process on the region of shared memory, wherein the first process identifier and the first operation are stored in an item of the first type within the data structure; and
on a second process other than the first process finishing accessing the region of shared memory, read the item and perform the first operation on behalf of the first process with a process other than the first process.
2. A data processing system as claimed in claim 1 , wherein the said operation is one of: an operation for storing data in the region of shared memory; and an operation for transmitting data from the region of shared memory.
3. A data processing system as claimed in claim 1 , wherein the data structure is further arranged to hold items of a second type each comprising an indication of another of the plurality of processes, which is attempting to access the region of shared memory, and an operation of waking the particular process; the data processing system being further arranged to, on a process finishing accessing the region of shared memory, wake the indicated process.
4. A data processing system as claimed in claim 3 , wherein the items of the second type held in the data structure are accessible only by an operating system arranged to control the data processing system.
5. A data processing system as claimed in claim 1 , wherein the data structure is stored in the region of shared memory.
6. A data processing system as claimed in claim 5 , wherein the data structure can be read by the operating system and at least some of the plurality of processes.
7. A data processing system as claimed in claim 1 , wherein the data structure is accessible by the operating system and at least some of the plurality of processes.
8. A data processing system as claimed in claim 7 , wherein the content of the data structure can be modified by the operating system and at least some of the plurality of processes.
9. A data processing system as claimed in claim 1 , wherein the data processing system is arranged to: on a process finishing accessing the region of shared memory, if the item is of the first type, perform the operation stored in that item on the region of shared memory with an operating system of the data processing system.
10. A data processing system as claimed in claim 9 , wherein the operating system is provided with application specific code for enabling the operating system to perform at least the operation.
11. A data processing system as claimed in claim 1 , wherein the data processing system is arranged to: on a process finishing accessing the region of shared memory, if the item is of the first type, perform the operation stored in that item on the region of shared memory with another of the plurality of processes.
12. A data processing system as claimed in claim 1 , wherein the data structure is a lockless data structure.
13. A data processing system arranged to control access by a plurality of processes to a region of shared memory, the data processing system being arranged to:
prevent more than one process from concurrently accessing the region of shared memory;
establish a data structure for holding items of a first type each comprising an identifier of a particular process that is attempting to access the region of shared memory, and an operation intended to be performed by the particular process on the region of shared memory;
on a process being denied access to the region of shared memory, store an item comprising an identifier of the process and an operation intended to be performed by the process in the data structure; and
on becoming permitted to access the region of shared memory, read an item in the data structure and perform the operation stored in that item with other than the process identified in that item.
14. A method for controlling access by a plurality of processes to a region of shared memory data in a data processing system, the method comprising:
preventing more than one process from concurrently accessing the region of shared memory;
establishing a data structure for holding items of a first type each comprising an identifier of a particular process that is attempting to access the region of shared memory, and an operation intended to be performed by the particular process on the region of shared memory;
storing the identifier of a first process that is attempting to access the region of shared memory, and an operation intended to be performed by the first process on the region of shared memory in the data structure; and
on a second process finishing accessing the region of shared memory, reading an item in the data structure and performing on behalf of a process identified in that item the operation stored in that item by other than the process identified in that item.
15. A method for controlling access by a plurality of processes to a region of shared memory in a data processing system, the method comprising:
preventing more than one process from concurrently accessing the region of shared memory;
establishing a data structure for holding items of a first type each comprising an identifier of a particular process attempting to access the region of shared memory, and an operation intended to be performed by the particular process on the region of shared memory;
storing an identifier of a first process attempting to access the region of shared memory, and an operation intended to be performed by the first process on the region of shared memory; and
on a second process becoming permitted to access the region of shared memory, reading an item in the data structure and performing on behalf of a process identified in that item the operation stored in that item by other than the process identified in that item.
16. A data processing system arranged to control access by a plurality of threads to a region of shared memory, the data processing system being arranged to:
prevent more than one thread from concurrently accessing the region of shared memory by means of a lock;
establish a data structure for holding items of a first type each comprising an identifier of a particular thread which is attempting to access the region of shared memory, and an operation intended to be performed by the particular thread on the region of shared memory; and
on a first thread finishing its use of the region of shared memory and on determining that the next item in the data structure indicates a second thread belonging to the same application as the first thread, passing the lock to the second thread indicated in that item without unlocking the lock.