Add event-chan argument to ev/go.

The event-chan is the final piece of the puzzle for fibers, and
will be pushed to when a fiber yields to the event loop.

src/core/ev.c

@@ -525,9 +525,14 @@ static void run_one(JanetFiber *fiber, Janet value, JanetSignal sigin) {
             JanetChannel *chan = (JanetChannel *)(fiber->done_channel);
             janet_channel_push(chan, janet_wrap_fiber(fiber), 2);
             fiber->done_channel = NULL;
+            fiber->event_channel = NULL;
+            fiber->new_channel = NULL;
         } else if (sig != JANET_SIGNAL_OK) {
             janet_stacktrace(fiber, res);
         }
+    } else if (fiber->event_channel) {
+        JanetChannel *chan = (JanetChannel *)(fiber->event_channel);
+        janet_channel_push(chan, janet_wrap_fiber(fiber), 2);
     }
 }
 
@@ -1977,15 +1982,18 @@ error:
 /* C functions */
 
 static Janet cfun_ev_go(int32_t argc, Janet *argv) {
-    janet_arity(argc, 1, 4);
+    janet_arity(argc, 1, 5);
     JanetFiber *fiber = janet_getfiber(argv, 0);
     Janet value = argc == 2 ? argv[1] : janet_wrap_nil();
     JanetChannel *done_channel = janet_optabstract(argv, argc, 2, &ChannelAT,
                                  janet_vm_root_fiber->done_channel);
     JanetChannel *new_channel = janet_optabstract(argv, argc, 3, &ChannelAT,
                                 janet_vm_root_fiber->new_channel);
+    JanetChannel *event_channel = janet_optabstract(argv, argc, 4, &ChannelAT,
+                                janet_vm_root_fiber->event_channel);
     fiber->done_channel = done_channel;
     fiber->new_channel = new_channel;
+    fiber->event_channel = event_channel;
     if (new_channel != NULL) {
         janet_channel_push((JanetChannel *) new_channel, janet_wrap_fiber(fiber), 2);
     }
@@ -2001,6 +2009,7 @@ static Janet cfun_ev_call(int32_t argc, Janet *argv) {
     fiber->env = janet_table(0);
     fiber->env->proto = janet_current_fiber()->env;
     fiber->done_channel = janet_vm_root_fiber->done_channel;
+    fiber->event_channel = janet_vm_root_fiber->event_channel;
     fiber->new_channel = janet_vm_root_fiber->new_channel;
     if (fiber->new_channel != NULL) {
         janet_channel_push((JanetChannel *) fiber->new_channel, janet_wrap_fiber(fiber), 2);
@@ -2110,10 +2119,19 @@ static const JanetReg ev_cfuns[] = {
     },
     {
         "ev/go", cfun_ev_go,
-        JDOC("(ev/go fiber &opt value chan)\n\n"
+        JDOC("(ev/go fiber &opt value done-chan new-chan event-chan)\n\n"
              "Put a fiber on the event loop to be resumed later. Optionally pass "
-             "a value to resume with, otherwise resumes with nil. If chan is provided, "
-             "the fiber will push itself to the channel upon completion or error. Returns the fiber.")
+             "a value to resume with, otherwise resumes with nil. Returns the fiber. "
+             "\n\n"
+             "Three optional `core/channel`s can be provided as well. These are channels "
+             "that will the fiber will be pushed to with `ev/give` on the relevant event. "
+             "\n\n"
+             "* `done-chan` - when `fiber` completes or errors, it will be pushed to this channel.\n"
+             "* `new-chan` - `fiber` will be pushed to this channel right away. Nested calls to `ev/go` "
+             "that don't set `new-chan` will also push to this channel.\n"
+             "* `event-chan` - when `fiber` yields to the event loop it will be pushed to this channel.\n\n"
+             "With these channels, the programmer can implement a \"supervisor\" for fibers for a fault "
+             "tolerant application.")
     },
     {
         "ev/sleep", cfun_ev_sleep,

src/core/fiber.c

@@ -42,6 +42,7 @@ static void fiber_reset(JanetFiber *fiber) {
     fiber->waiting = NULL;
     fiber->sched_id = 0;
     fiber->done_channel = NULL;
+    fiber->event_channel = NULL;
     fiber->new_channel = NULL;
 #endif
     janet_fiber_set_status(fiber, JANET_STATUS_NEW);
@@ -87,6 +88,7 @@ JanetFiber *janet_fiber_reset(JanetFiber *fiber, JanetFunction *callee, int32_t
 #ifdef JANET_EV
     fiber->waiting = NULL;
     fiber->done_channel = NULL;
+    fiber->event_channel = NULL;
     fiber->new_channel = NULL;
 #endif
     return fiber;

src/core/gc.c

@@ -271,6 +271,9 @@ recur:
     if (fiber->done_channel) {
         janet_mark_abstract(fiber->done_channel);
     }
+    if (fiber->event_channel) {
+        janet_mark_abstract(fiber->event_channel);
+    }
     if (fiber->new_channel) {
         janet_mark_abstract(fiber->new_channel);
     }

src/include/janet.h

@@ -840,9 +840,14 @@ struct JanetFiber {
     JanetFiber *child; /* Keep linked list of fibers for restarting pending fibers */
     Janet last_value; /* Last returned value from a fiber */
 #ifdef JANET_EV
+    /* These fields are only relevant for fibers that are used as "root fibers" -
+     * that is, fibers that are scheduled on the event loop and behave much like threads
+     * in a multi-tasking system. It would be possible to move these fields to a new
+     * type, say "JanetTask", that as separate from fibers to save a bit of space. */
     JanetListenerState *waiting;
     uint32_t sched_id; /* Increment everytime fiber is scheduled by event loop */
     void *done_channel; /* Channel to push self to when complete */
+    void *event_channel; /* Channel to push self to when yielding to event loop */
     void *new_channel; /* Channel to push spawned children */
 #endif
 };