Categories: Open C | How To

This page was last modified 01:06, 2 October 2007.

From Forum Nokia Wiki

Introduction

The following mechanisms are used to communicate between two threads within a process and also between unrelated processes(created either by a Symbian app or Open C application):

• Pipes
• Named pipes
• Message queues
• Shared memory

Pipes

Pipes can be used when a process creates child processes or threads and wants to communicate with them. The following steps are needed to do so:

• Declare a global variable with array [2] of data type int.
• Create a pipe.
• Create a thread.
• Read data from the pipe from the parent thread.
• Write data from the child thread.
• Close the read or write descriptor

Pipes Example

Named pipes

Named pipes(mkfifo) are used to communicate between threads within a process or between two unrelated processes. The following steps are needed to do so:

• Create a named pipe using mkfifo.
• Create a process or thread and open this pipe in write mode.
• Another process or thread can open the same in read mode.
• Close the read or write descriptor.

Named Pipes Example

Message queues

Message queues are used to communicate between threads within a process or two unrelated processes. The following steps are needed to do so:

• Create a message queue using msgget.
• Create a process or thread and send some message to this message queue.
• Read the message from the main thread.
• Delete the message queue.

Message Queues Example

Shared memory

Shared memory is used to communicate between threads within a process or two unrelated processes, allowing both to share a given region of memory. The following steps are needed to do so:

• Create a shared memory segment using shmget<tt>.
• Attach the segment to the address space of both processes using <tt>shmat.
• Synchronize processes to correct access the shared memory.
• Detach the shared memory segment from the address space of the processes using shmdt.

Shared Memory Example