sharedmemory

Shared memory is an inter-process communication mechanism that allows two or more processes to access a common region of memory. By sharing memory, processes can exchange data with minimal copying, enabling high-throughput, low-latency communication on the same host.

Typically, one process creates a memory object or segment and then maps it into its own address space; the same region is subsequently mapped into other processes. Access must be coordinated with synchronization primitives such as mutexes or semaphores to avoid data races. Depending on the implementation, the region may be anonymous (not associated with a filesystem object) or backed by a file or device.

Common implementations include POSIX shared memory (shm_open, mmap), System V shared memory (shmget, shmat), and Windows memory-mapped files (CreateFileMapping, MapViewOfFile). On Unix-like systems, anonymous mappings can also be used with shared memory semantics via mmap with MAP_SHARED. Some systems also provide named shared memory objects stored in a virtual filesystem like /dev/shm.

Shared memory offers high performance but introduces synchronization and lifetime management challenges. It is best suited for large data structures or streaming data between closely cooperating processes. Security considerations include proper permissions and explicit cleanup to avoid leaks. It is typically limited to processes on the same machine; distributed shared memory exists as a separate research and product area but is not a standard IPC primitive.

Related concepts include memory-mapped files and other IPC mechanisms such as pipes and sockets. Implementers should consider portability across platforms and the appropriate APIs for their target environment.