07_sleep.c

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/* -*- C -*-
 * Serene programming language
 * Copyright (C) 2019-2026 Sameer Rahmani <[email protected]>
 *
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <https://www.gnu.org/licenses/>.
 */
 
// Example 07 -- sleeping without blocking the worker.
//
// srn_fiber_sleep_ms parks the calling fiber for a duration and lets its worker run
// other fibers meanwhile. The reactor holds a timer per sleeper and wakes it
// once its deadline passes. This is also why running out of runnable fibers no
// longer ends a run: the reactor keeps it alive while any timer (or IO) is
// outstanding, and the run ends only once nothing is runnable AND nothing is in
// flight.
//
// Three fibers sleep for different spans. On a single worker they park almost at
// once, then wake in deadline order (100, 200, 300 ms) rather than creation
// order, because the reactor fires timers by their deadline.
 
#include <stdint.h>
#include <stdio.h>
 
#include <serene/rt/fiber/io.h>
#include <serene/runtime.h>
 
typedef struct {
  const char *name;
  uint64_t ms;
} sleeper_args_t;
 
static srn_fiber_result_t sleeper(srn_context_t *ctx, void *arg) {
  (void)ctx;
  sleeper_args_t *a = arg;
  printf("%s: sleeping %llu ms\n", a->name, (unsigned long long)a->ms);
  srn_error_t *err = srn_fiber_sleep_ms(a->ms);
  printf("%s: woke up (%s)\n", a->name, err == nullptr ? "ok" : err->msg);
  return nullptr;
}
 
int main(void) {
  SERENE_RUNTIME_INIT_WITH_SCHED(engine, sched, nullptr);
  srn_context_t *ctx = srn_context_make(engine);
 
  sleeper_args_t a = {"A", 300};
  sleeper_args_t b = {"B", 100};
  sleeper_args_t c = {"C", 200};
  (void)srn_fiber_spawn(ctx, sleeper, &a);
  (void)srn_fiber_spawn(ctx, sleeper, &b);
  (void)srn_fiber_spawn(ctx, sleeper, &c);
 
  // One worker: all three park on their timers, and the run stays alive until
  // the last timer fires -- the reactor keeps it from going quiescent early.
  srn_sched_run(sched, 1);
  printf("all sleepers done\n");
 
  srn_context_release(ctx);
  SERENE_RUNTIME_SHUTDOWN(engine);
  return 0;
}