cocall

cocall

Pass Control to a Coprocess

SYNOPSIS
DESCRIPTION
RETURN VALUE
CAUTIONS
EXAMPLE

SYNOPSIS

#include <coproc.h>

void *cocall(coproc_t procid, void *arg);

DESCRIPTION

The cocall function gives control to a coprocess and passes it a pointer value. Execution of the calling coprocess is suspended until the called coprocess calls coreturn or is terminated. The procid argument identifies the coprocess to be called. The arg value is a value passed to the called coprocess. arg must not have the value CO_ERR . The arg value is passed to the called coprocess as follows: The arg value is passed to the called coprocess as follows:

If this coprocess has not been called previously, its initial function (as established when the coprocess was costarted) is invoked with the specified argument value. For example, the following sequence executes the function call (*f)(arg) that begins executing the coprocess created by the costart call:
```
id = costart(f,NULL);
cocall(id,arg);
```
If the called coprocess has been called previously, it is necessarily suspended as a result of the execution of a call to the coreturn function. In this case, the suspended call to coreturn is resumed, and coreturn returns the value specified by arg .

RETURN VALUE

cocall returns a pointer specified by the called coprocess. Depending on the circumstances, any of the following can occur. If the called coprocess suspends itself by calling coreturn(val) , the value val is returned by cocall . If the called coprocess terminates by calling coexit(val) , the value val is returned by cocall . If the called coprocess terminates as a result of execution of return val; by its initial function, the value val is returned by cocall .

If the procid argument is invalid (that is, if it identifies an invalid or If the procid argument is invalid (that is, if it identifies an invalid or terminated coprocess), the calling coprocess is not suspended, and cocall immediately returns the constant CO_ERR .

CAUTIONS

Recursive cocall s are not allowed. While a coprocess is suspended as the result of a call to cocall , it cannot be cocalled again. In particular, the main coprocess can never be cocalled. Any attempt to perform a recursive cocall returns CO_ERR .

EXAMPLE

#include <stddef.h>
#include <coproc.h>
#include <stdlib.h>

coproc_t inp_proc;           /* input process process ID           */

void *input(void *);

char *file_name = "ddn:input";
char *input_ln;           /* a line of input, returned by inp_proc */

   /* Create and call a coprocess that reads a line of data from a */
   /* file. The "input" function, which is the initial function of */
   /* the new coprocess, is given in the EXAMPLE for coreturn.     */

inp_proc = costart(&input,NULL);          /* Create the coprocess. */

   /* Pass the input file name and check for error.                */
if (!cocall(inp_proc, file_name))
   exit(16);

for (;;) {
   input_ln = cocall(inp_proc, NULL);

         /* Ask for an input line; stop if no data left.           */
   if (!input_ln) break;
   .
   .   /* Process input data.                                      */
   .
}

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