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what is main difference between shared memory and pipe in unix programming?
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A pipe is a section of shared memory that processes use for communication. The process that creates a pipe is the pipe server. A process that connects to a pipe is a pipe client. One process writes information to the pipe, then the other process reads the information from the pipe.
IPC messages mimic the reading and writing of files. They are easier to use than pipes when more than two processes must communicate by using a single medium. The IPC shared semaphore facility provides process synchronization. Shared memory is the fastest form of interprocess communication.
It's message passing. You specify a buffer to write into the socket buffer, and you find out how much space it has available beforehand using getTxAvailable() or whatever. It's not really shared memory as it does a buffer blit operation to help encapsulation of the socket.
Message queue has inherent synchronization overhead, guarantee of safety at cost of performance. Shared memory has no safeguards - if two threads access it simultaneously, they will possibly conflict (write inconsistent data) unless you assure thread safety yourself.
Taken from this article
(unnamed) Pipes
Shared Memory
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Shared Memory Vs Pipe-
Kernel-
Once Shared Memory is setup by the kernel there is no further need of kernel for the communication b/w process whereas in Pipe, data is buffered in the kernel space and requires system call for each access. Here, Shared Memory is faster than Pipe. It is a major drawback of the pipe becuase IPC is important for the computational speed up.
Communication
Shared Memory- Bidirectional whereas Pipe(unnamed Pipe)- Unidirectional.
Reliable
Shared Memory- Less Reliable(data mix up) whereas Pipe is more Reliable as data is buffered and is under control of the kernel.
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