protothread/example-small.c

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2022-11-22 01:59:34 +00:00
/**
* This is a very small example that shows how to use
* protothreads. The program consists of two protothreads that wait
* for each other to toggle a variable.
*/
/* We must always include pt.h in our protothreads code. */
#include "pt.h"
#include <stdio.h> /* For printf(). */
/* Two flags that the two protothread functions use. */
static int protothread1_flag, protothread2_flag;
/**
* The first protothread function. A protothread function must always
* return an integer, but must never explicitly return - returning is
* performed inside the protothread statements.
*
* The protothread function is driven by the main loop further down in
* the code.
*/
static int
protothread1(struct pt *pt)
{
/* A protothread function must begin with PT_BEGIN() which takes a
pointer to a struct pt. */
PT_BEGIN(pt);
/* We loop forever here. */
while(1) {
/* Wait until the other protothread has set its flag. */
PT_WAIT_UNTIL(pt, protothread2_flag != 0);
printf("Protothread 1 running\n");
/* We then reset the other protothread's flag, and set our own
flag so that the other protothread can run. */
protothread2_flag = 0;
protothread1_flag = 1;
/* And we loop. */
}
/* All protothread functions must end with PT_END() which takes a
pointer to a struct pt. */
PT_END(pt);
}
/**
* The second protothread function. This is almost the same as the
* first one.
*/
static int
protothread2(struct pt *pt)
{
PT_BEGIN(pt);
while(1) {
/* Let the other protothread run. */
protothread2_flag = 1;
/* Wait until the other protothread has set its flag. */
PT_WAIT_UNTIL(pt, protothread1_flag != 0);
printf("Protothread 2 running\n");
/* We then reset the other protothread's flag. */
protothread1_flag = 0;
/* And we loop. */
}
PT_END(pt);
}
/**
* Finally, we have the main loop. Here is where the protothreads are
* initialized and scheduled. First, however, we define the
* protothread state variables pt1 and pt2, which hold the state of
* the two protothreads.
*/
static struct pt pt1, pt2;
int
main(void)
{
/* Initialize the protothread state variables with PT_INIT(). */
PT_INIT(&pt1);
PT_INIT(&pt2);
/*
* Then we schedule the two protothreads by repeatedly calling their
* protothread functions and passing a pointer to the protothread
* state variables as arguments.
*/
while(1) {
protothread1(&pt1);
protothread2(&pt2);
}
}