95 lines
1.8 KiB
C
95 lines
1.8 KiB
C
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#include <assert.h>
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#include <stddef.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <time.h>
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#include <libucontext/libucontext.h>
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libucontext_ucontext_t mainctx = {};
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libucontext_ucontext_t *curthr = &mainctx;
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libucontext_ucontext_t *threads = NULL;
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size_t thrcount = 0;
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void
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yieldto(libucontext_ucontext_t *target)
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{
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libucontext_ucontext_t *oldthr = curthr;
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curthr = target;
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libucontext_swapcontext(oldthr, curthr);
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}
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void
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yield(void)
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{
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libucontext_ucontext_t *newthr;
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/* we set uc_flags to non-zero to signal thread completion. */
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do
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newthr = &threads[random() % thrcount];
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while (newthr == curthr || newthr->uc_flags);
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srandom(time(NULL));
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yieldto(newthr);
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}
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void
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worker(size_t multiple)
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{
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size_t accum = 1;
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for (size_t i = 0; i < 10; i++)
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{
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accum += (multiple * i);
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printf("[%p] accumulated %zu\n", curthr, accum);
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yield();
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}
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/* mark thread as completed, so we don't return here */
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curthr->uc_flags = 1;
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}
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void
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create(size_t multiple)
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{
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libucontext_ucontext_t *cursor;
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thrcount += 1;
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threads = realloc(threads, sizeof(*threads) * thrcount);
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cursor = &threads[thrcount - 1];
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memset(cursor, '\0', sizeof *cursor);
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/* initialize the new thread's values to our current context */
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libucontext_getcontext(cursor);
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/* set up uc_link */
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cursor->uc_link = thrcount > 1 ? &threads[thrcount - 2] : &mainctx;
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/* set up a stack */
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cursor->uc_stack.ss_size = 8192;
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cursor->uc_stack.ss_sp = calloc(1, cursor->uc_stack.ss_size);
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/* set up the function call */
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libucontext_makecontext(cursor, worker, 1, multiple);
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}
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int
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main(int argc, const char *argv[])
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{
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srandom(time(NULL));
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libucontext_getcontext(&mainctx);
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for (size_t i = 1; i < 4; i++)
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create(i);
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/* start the threads off by yielding to the last one */
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yieldto(&threads[thrcount - 1]);
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return EXIT_SUCCESS;
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}
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