01_hello.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 01 -- hello fiber.
//
// The smallest complete fiber program. It shows the bootstrap every other
// example repeats: build a memory manager, an engine, and a context, reach the
// scheduler the engine already created, spawn one fiber, then run the scheduler
// until the work drains.
//
// A fiber's entry has the shape `srn_fiber_result_t (srn_context_t *, void *)`.
// It returns a non-null result. The launcher rejects a null result, so a fiber
// with nothing to report returns the address of a shared sentinel.
 
#include <stdio.h>
 
#include <serene/runtime.h>
 
// A fiber result has to be non-null. This sentinel stands in for a fiber that
// produces no meaningful value.
static int ok;
 
static srn_fiber_result_t say_hello(srn_context_t *ctx, void *arg) {
  (void)ctx;
  (void)arg;
  printf("hello from a fiber\n");
  return &ok;
}
 
int main(void) {
  srn_mm_t *mm = srn_mm_init();
  srn_engine_t *engine = srn_engine_make(mm);
  srn_context_t *ctx = srn_context_make(engine);
 
  // The engine creates one scheduler at startup and keeps it on `scheduler`.
  srn_scheduler_t *sched = engine->scheduler;
 
  // Create the fiber. It is registered and made ready, but nothing runs until
  // the scheduler does.
  srn_fiber_t *fiber = srn_fiber_make(ctx, sched, say_hello, nullptr, 0);
 
  // Drive the scheduler on this one thread. It returns once the fiber has run
  // and the ready queue is empty.
  srn_sched_run(sched, 1);
 
  printf("fiber finished in state %d\n", (int)fiber->state);
 
  srn_context_release(ctx);
  srn_engine_shutdown(engine);
  srn_mm_shutdown(mm);
  return 0;
}