Shared memory

On the other hand, it is less scalable, as for example the communicating processes must be running on the same machine (of other IPC methods, only Internet domain sockets—not Unix domain sockets—can use a computer network), and care must be taken to avoid issues if processes sharing memory are running on separate CPUs and the underlying architecture is not cache coherent.

IPC by shared memory is used for example to transfer images between the application and the X server on Unix systems, or inside the IStream object returned by CoMarshalInterThreadInterfaceInStream in the COM libraries under Windows.

Dynamic libraries are generally held in memory once and mapped to multiple processes, and only pages that had to be customized for the individual process (because a symbol resolved differently there) are duplicated, usually with a mechanism known as copy-on-write that transparently copies the page when a write is attempted, and then lets the write succeed on the private copy.

This has a drawback in that if the process crashes and fails to clean up shared memory it will stay until system shutdown; that limitation is not present in an Android-specific implementation dubbed ashmem.

[7] On Windows, one can use CreateFileMapping and MapViewOfFile functions to map a region of a file into memory in multiple processes.

[10] For programming languages with POSIX bindings (say, C/C++), shared memory regions can be created and accessed by calling the functions provided by the operating system.