backend/epoll: implement eventfd wakeup notification (#128)

Tries to mimic what happens in backend/kqueue.

Closes #4

src/backend/epoll.zig

@@ -21,6 +21,12 @@ pub const Loop = struct {
 
     fd: posix.fd_t,
 
+    /// The eventfd that this epoll queue always has a filter for. Writing
+    /// an empty message to this eventfd can be used to wake up the loop
+    /// at any time. Waking up the loop via this eventfd won't trigger any
+    /// particular completion, it just forces tick to cycle.
+    eventfd: xev.Async,
+
     /// The number of active completions. This DOES NOT include completions that
     /// are queued in the submissions queue.
     active: usize = 0,
@@ -56,8 +62,12 @@ pub const Loop = struct {
     } = .{},
 
     pub fn init(options: xev.Options) !Loop {
+        var eventfd = try xev.Async.init();
+        errdefer eventfd.deinit();
+
         var res: Loop = .{
             .fd = try posix.epoll_create1(std.os.linux.EPOLL.CLOEXEC),
+            .eventfd = eventfd,
             .thread_pool = options.thread_pool,
             .thread_pool_completions = undefined,
             .cached_now = undefined,
@@ -68,6 +78,7 @@ pub const Loop = struct {
 
     pub fn deinit(self: *Loop) void {
         posix.close(self.fd);
+        self.eventfd.deinit();
     }
 
     /// Run the event loop. See RunMode documentation for details on modes.
@@ -262,20 +273,51 @@ pub const Loop = struct {
         // Initialize
         if (!self.flags.init) {
             self.flags.init = true;
+
             if (self.thread_pool != null) {
                 self.thread_pool_completions.init();
             }
+
+            var ev: linux.epoll_event = .{
+                .events = linux.EPOLL.IN | linux.EPOLL.RDHUP,
+                .data = .{ .fd = self.eventfd.fd },
+            };
+            posix.epoll_ctl(
+                self.fd,
+                linux.EPOLL.CTL_ADD,
+                self.eventfd.fd,
+                &ev,
+            ) catch |err| {
+                // We reset initialization because we can't do anything
+                // safely unless we get this mach port registered!
+                self.flags.init = false;
+                return err;
+            };
         }
 
         // Submit all the submissions. We copy the submission queue so that
         // any resubmits don't cause an infinite loop.
+        var wait_rem: usize = @intCast(wait);
         var queued = self.submissions;
         self.submissions = .{};
         while (queued.pop()) |c| {
             // We ignore any completions that aren't in the adding state.
             // This usually means that we switched them to be deleted or
             // something.
             if (c.flags.state != .adding) continue;
+
+            // These operations happen synchronously. Ensure they are
+            // decremented from wait_rem.
+            switch (c.op) {
+                .cancel,
+                // should noop be counted?
+                // .noop,
+                .shutdown,
+                .timer,
+                => wait_rem -|= 1,
+                else => {},
+            }
+
             self.start(c);
         }
 
@@ -294,7 +336,6 @@ pub const Loop = struct {
 
         // Wait and process events. We only do this if we have any active.
         var events: [1024]linux.epoll_event = undefined;
-        var wait_rem: usize = @intCast(wait);
         while (self.active > 0 and (wait == 0 or wait_rem > 0)) {
             self.update_now();
             const now_timer: Operation.Timer = .{ .next = self.cached_now };
@@ -347,9 +388,7 @@ pub const Loop = struct {
             const timeout: i32 = if (wait_rem == 0) 0 else timeout: {
                 // If we have a timer, we want to set the timeout to our next
                 // timer value. If we have no timer, we wait forever.
-                // TODO: do not wait 100ms here, use an eventfd for our
-                // thread pool to wake us up.
-                const t = self.timers.peek() orelse break :timeout 100;
+                const t = self.timers.peek() orelse break :timeout -1;
 
                 // Determine the time in milliseconds.
                 const ms_now = @as(u64, @intCast(self.cached_now.tv_sec)) * std.time.ms_per_s +
@@ -369,6 +408,13 @@ pub const Loop = struct {
 
             // Process all our events and invoke their completion handlers
             for (events[0..n]) |ev| {
+                // Handle wakeup eventfd
+                if (ev.data.fd == self.eventfd.fd) {
+                    var buffer: u64 = undefined;
+                    _ = posix.read(self.eventfd.fd, std.mem.asBytes(&buffer)) catch {};
+                    continue;
+                }
+
                 const c: *Completion = @ptrFromInt(@as(usize, @intCast(ev.data.ptr)));
 
                 // We get the fd and mark this as in progress we can properly
@@ -415,6 +461,7 @@ pub const Loop = struct {
         const pool = self.thread_pool orelse return error.ThreadPoolRequired;
 
         // Setup our completion state so that thread_perform can do stuff
+        c.task_loop = self;
         c.task_completions = &self.thread_pool_completions;
         c.task = .{ .callback = Loop.thread_perform };
 
@@ -436,6 +483,14 @@ pub const Loop = struct {
 
         // Add to our completion queue
         c.task_completions.push(c);
+
+        // Wake up our main loop
+        c.task_loop.wakeup() catch {};
+    }
+
+    /// Sends an empty message to this loop's eventfd so that it wakes up.
+    fn wakeup(self: *Loop) !void {
+        try self.eventfd.notify();
     }
 
     fn start(self: *Loop, completion: *Completion) void {
@@ -658,6 +713,13 @@ pub const Loop = struct {
             },
 
             .close => |v| res: {
+                if (completion.flags.threadpool) {
+                    if (self.thread_schedule(completion)) |_|
+                        return
+                    else |err|
+                        break :res .{ .close = err };
+                }
+
                 posix.close(v.fd);
                 break :res .{ .close = {} };
             },
@@ -800,6 +862,7 @@ pub const Completion = struct {
     /// reliable way to get access to the loop and shouldn't be used
     /// except internally.
     task: ThreadPool.Task = undefined,
+    task_loop: *Loop = undefined,
     task_completions: *Loop.TaskCompletionQueue = undefined,
     task_result: Result = undefined,
 
@@ -866,7 +929,6 @@ pub const Completion = struct {
             // This should never happen because we always do these synchronously
             // or in another location.
             .cancel,
-            .close,
             .noop,
             .shutdown,
             .timer,
@@ -972,6 +1034,11 @@ pub const Completion = struct {
                         err,
                 };
             },
+
+            .close => |*op| res: {
+                posix.close(op.fd);
+                break :res .{ .close = {} };
+            },
         };
     }
 
@@ -1234,7 +1301,7 @@ pub const AcceptError = posix.EpollCtlError || error{
     Unknown,
 };
 
-pub const CloseError = posix.EpollCtlError || error{
+pub const CloseError = posix.EpollCtlError || ThreadPoolError || error{
     Unknown,
 };
 

src/backend/kqueue.zig

@@ -1106,7 +1106,6 @@ pub const Completion = struct {
     fn perform(self: *Completion, ev_: ?*const Kevent) Result {
         return switch (self.op) {
             .cancel,
-            .close,
             .noop,
             .timer,
             .shutdown,
@@ -1236,6 +1235,11 @@ pub const Completion = struct {
 
                 break :res .{ .proc = 0 };
             },
+
+            .close => |*op| res: {
+                posix.close(op.fd);
+                break :res .{ .close = {} };
+            },
         };
     }
 

src/watcher/stream.zig

@@ -80,6 +80,22 @@ pub fn Closeable(comptime xev: type, comptime T: type, comptime options: Options
                 }).callback,
             };
 
+            // If we're dup-ing, then we ask the backend to manage the fd.
+            switch (xev.backend) {
+                .io_uring,
+                .wasi_poll,
+                .iocp,
+                => {},
+
+                .epoll => {
+                    c.flags.threadpool = true;
+                },
+
+                .kqueue => {
+                    c.flags.threadpool = true;
+                },
+            }
+
             loop.add(c);
         }
     };