Coroutines: A simple and lightweight parallel execution framework.

lib/coro.h

@@ -0,0 +1,26 @@
+/*
+ *	BIRD Coroutines
+ *
+ *	(c) 2017 Martin Mares <mj@ucw.cz>
+ *	(c) 2020 Maria Matejka <mq@jmq.cz>
+ *
+ *	Can be freely distributed and used under the terms of the GNU GPL.
+ */
+
+#ifndef _BIRD_CORO_H_
+#define _BIRD_CORO_H_
+
+#include "lib/resource.h"
+
+/* A completely opaque coroutine handle. */
+struct coroutine;
+
+/* Coroutines are independent threads bound to pools.
+ * You request a coroutine by calling coro_run().
+ * It is forbidden to free a running coroutine from outside.
+ * The running coroutine must free itself by rfree() before returning.
+ */
+struct coroutine *coro_run(pool *, void (*entry)(void *), void *data);
+
+
+#endif

sysdep/unix/coroutine.c

@@ -17,7 +17,14 @@
 
 #include "lib/birdlib.h"
 #include "lib/locking.h"
+#include "lib/coro.h"
 #include "lib/resource.h"
+#include "lib/timer.h"
+
+/* Using a rather big stack for coroutines to allow for stack-local allocations.
+ * In real world, the kernel doesn't alloc this memory until it is used.
+ * */
+#define CORO_STACK_SIZE	1048576
 
 /*
  *	Implementation of coroutines based on POSIX threads
@@ -100,3 +107,69 @@ void do_unlock(struct domain_generic *dg, struct domain_generic **lsp)
   pthread_mutex_unlock(&dg->mutex);
 }
 
+/* Coroutines */
+struct coroutine {
+  resource r;
+  pthread_t id;
+  pthread_attr_t attr;
+  void (*entry)(void *);
+  void *data;
+};
+
+static _Thread_local _Bool coro_cleaned_up = 0;
+
+static void coro_free(resource *r)
+{
+  struct coroutine *c = (void *) r;
+  ASSERT_DIE(pthread_equal(pthread_self(), c->id));
+  pthread_attr_destroy(&c->attr);
+  coro_cleaned_up = 1;
+}
+
+static struct resclass coro_class = {
+  .name = "Coroutine",
+  .size = sizeof(struct coroutine),
+  .free = coro_free,
+};
+
+extern pthread_key_t current_time_key;
+
+static void *coro_entry(void *p)
+{
+  struct coroutine *c = p;
+  ASSERT_DIE(c->entry);
+
+  pthread_setspecific(current_time_key, &main_timeloop);
+
+  c->entry(c->data);
+  ASSERT_DIE(coro_cleaned_up);
+
+  return NULL;
+}
+
+struct coroutine *coro_run(pool *p, void (*entry)(void *), void *data)
+{
+  ASSERT_DIE(entry);
+  ASSERT_DIE(p);
+
+  struct coroutine *c = ralloc(p, &coro_class);
+
+  c->entry = entry;
+  c->data = data;
+
+  int e = 0;
+
+  if (e = pthread_attr_init(&c->attr))
+    die("pthread_attr_init() failed: %M", e);
+
+  if (e = pthread_attr_setstacksize(&c->attr, CORO_STACK_SIZE))
+    die("pthread_attr_setstacksize(%u) failed: %M", CORO_STACK_SIZE, e);
+
+  if (e = pthread_attr_setdetachstate(&c->attr, PTHREAD_CREATE_DETACHED))
+    die("pthread_attr_setdetachstate(PTHREAD_CREATE_DETACHED) failed: %M", e);
+
+  if (e = pthread_create(&c->id, &c->attr, coro_entry, c))
+    die("pthread_create() failed: %M", e);
+
+  return c;
+}

sysdep/unix/io.c

@@ -2176,6 +2176,15 @@ static int short_loops = 0;
 #define SHORT_LOOP_MAX 10
 #define WORK_EVENTS_MAX 10
 
+static int poll_reload_pipe[2];
+
+void
+io_loop_reload(void)
+{
+  char b;
+  write(poll_reload_pipe[1], &b, 1);
+}
+
 void
 io_loop(void)
 {
@@ -2187,6 +2196,9 @@ io_loop(void)
   int fdmax = 256;
   struct pollfd *pfd = xmalloc(fdmax * sizeof(struct pollfd));
 
+  if (pipe(poll_reload_pipe) < 0)
+    die("pipe(poll_reload_pipe) failed: %m");
+
   watchdog_start1();
   for(;;)
     {
@@ -2205,7 +2217,12 @@ io_loop(void)
 	poll_tout = MIN(poll_tout, timeout);
       }
 
-      nfds = 0;
+      /* A hack to reload main io_loop() when something has changed asynchronously. */
+      pfd[0].fd = poll_reload_pipe[0];
+      pfd[0].events = POLLIN;
+
+      nfds = 1;
+
       WALK_LIST(n, sock_list)
 	{
 	  pfd[nfds] = (struct pollfd) { .fd = -1 }; /* everything other set to 0 by this */
@@ -2277,6 +2294,14 @@ io_loop(void)
 	}
       if (pout)
 	{
+	  if (pfd[0].revents & POLLIN)
+	  {
+	    /* IO loop reload requested */
+	    char b;
+	    read(poll_reload_pipe[0], &b, 1);
+	    continue;
+	  }
+
 	  times_update(&main_timeloop);
 
 	  /* guaranteed to be non-empty */

sysdep/unix/unix.h

@@ -106,6 +106,7 @@ extern volatile sig_atomic_t async_shutdown_flag;
 
 void io_init(void);
 void io_loop(void);
+void io_loop_reload(void);
 void io_log_dump(void);
 int sk_open_unix(struct birdsock *s, char *name);
 struct rfile *rf_open(struct pool *, const char *name, const char *mode);