Coprocessing Functions

Restrictions

You should be aware of the following restrictions and special considerations when coprocesses are used. In addition, certain advanced topics that are important to a few complex applications are described here, after the example. You may want to skip these sections if they are not relevant to your application.

At most, 65,536 coprocesses can be defined at one time, including the main coprocess. Coprocesses that have ended are not included in this count.
Each coprocess has its own stack and automatic storage. The initial stack allocation run-time option applies only to the main coprocess. All other coprocesses are given an initial stack allocation of 4096 bytes unless some other size is requested by the call to costart . However, each coprocess' stack space is expanded dynamically as necessary.
You may not use the minimal form of program linkage (the =minimal run-time option or its compile-time equivalent) in an application that uses coprocesses.
Each coprocess has its own quiet setting. A call to the quiet function in one coprocess has no effect on diagnostic messages generated by another.
Signal handling in a coprocessing environment requires special care. See Advanced Topics: Signal Handling for more information.
If any coprocess calls the exit function, the entire program is terminated. The details of program termination are described in Advanced Topics: Program Termination. A call to coexit in the main coprocess is treated as a call to exit .
longjmp cannot be used to transfer control between coprocesses. In particular, you cannot call setjmp in one coprocess and call longjmp using the same jmp_buf in another. Any attempt to do this causes abnormal program termination.
Memory allocated via malloc is shared by all coprocesses. Memory allocated by one coprocess can be freed by another. Similarly, load modules loaded by one process can be used or unloaded by another, and files opened by one coprocess can be used or closed by another.
There is no restriction against using the same function as the initial function of several coprocesses. In fact, as the following example shows, this can be a useful technique.

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