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The C POSIX library is a specification of a C standard library for POSIX systems. It was developed at the same time as the ANSI C standard. Some effort was made to make POSIX compatible with standard C ; POSIX includes additional functions to those introduced in standard C.
SHMEM (from Cray Research's “shared memory” library [1]) is a family of parallel programming libraries, providing one-sided, RDMA, parallel-processing interfaces for low-latency distributed-memory supercomputers. The SHMEM acronym was subsequently reverse engineered to mean "Symmetric Hierarchical MEMory”. [2]
POSIX also provides the mmap API for mapping files into memory; a mapping can be shared, allowing the file's contents to be used as shared memory. Linux distributions based on the 2.6 kernel and later offer /dev/shm as shared memory in the form of a RAM disk , more specifically as a world-writable directory (a directory in which every user of ...
All POSIX systems, Windows, AmigaOS 2.0+ Shared memory: Multiple processes are given access to the same block of memory, which creates a shared buffer for the processes to communicate with each other. All POSIX systems, Windows Message passing: Allows multiple programs to communicate using message queues and/or non-OS managed channels.
The break value can be automatically rounded up to a size appropriate for the memory management architecture. [4] sbrk and brk were considered legacy even by 1997 standards (Single UNIX Specification v2 or POSIX.1-1998). [5] They were removed in POSIX.1-2001. [6]
The main difference between System V shared memory (shmem) and memory mapped I/O (mmap) is that System V shared memory is persistent: unless explicitly removed by a process, it is kept in memory and remains available until the system is shut down. mmap'd memory is not persistent between application executions (unless it is backed by a file).
The child borrows the memory management unit setup from the parent and memory pages are shared among the parent and child process with no copying done, and in particular with no copy-on-write semantics; [10] hence, if the child process makes a modification in any of the shared pages, no new page will be created and the modified pages are ...
The use of shared memory and an atomic test-and-set instruction provide the mutual exclusion. A process can test-and-set on a location in shared memory, and since the operation is atomic, only one process can set the flag at a time. Any process that is unsuccessful in setting the flag can either go on to do other tasks and try again later ...