coro: remove io_ack from scheduler

The logic here is not sound and actually is the root cause for #31
The yield enough should be enough for valid io submission, in theory if
the task is cancelled immediately something weird could happen.. It is
better to implement #44 to make sure no such bug exists and are catch
early.

Fixes #31

bugs/31.zig

@@ -63,9 +63,10 @@ pub fn spawner(tmp: []usize) !void {
     for (0..500) |i| {
         _ = try scheduler.spawn(protection, .{ logger, .{ i, tmp } }, .{});
     }
-    try delay(std.time.ns_per_s * 25); // logging takes 20s + 5s for safety
+    try delay(std.time.ns_per_s * 25); // logging takes ~25s
     for (tmp, 0..) |value, index| {
         logInfo("{}. {}\n", .{ index + 1, value });
+        if (value != 100) @panic("something went bonkers (2)");
     }
     //just test for protection layer
     return error.Unexpected;

build.zig

@@ -112,7 +112,7 @@ pub fn build(b: *std.Build) void {
     const bug_step = b.step("bug", "Run regression tests");
     inline for (.{
         .@"22",
-        // .@"31", TODO: fix this
+        .@"31",
     }) |bug| {
         const exe = b.addExecutable(.{
             .name = @tagName(bug),

src/coro/Scheduler.zig

@@ -6,7 +6,6 @@ const options = @import("../coro.zig").options;
 
 allocator: std.mem.Allocator,
 io: aio.Dynamic,
-io_ack: u8 = 0,
 running: Frame.List = .{},
 completed: Frame.List = .{},
 state: enum { init, tear_down } = .init,
@@ -83,7 +82,6 @@ pub fn spawn(self: *@This(), comptime func: anytype, args: anytype, opts: SpawnO
 /// Returns the number of tasks running.
 pub fn tick(self: *@This(), mode: aio.Dynamic.CompletionMode) aio.Error!usize {
     if (self.state == .tear_down) return error.Unexpected;
-    self.io_ack +%= 1;
     if (self.completed.first) |first| {
         var next: ?*Frame.List.Node = first;
         while (next) |node| {

src/coro/io.zig

@@ -49,10 +49,7 @@ pub fn do(operations: anytype, status: Frame.Status) Error!u16 {
         }
 
         // wait until scheduler actually submits our work
-        const ack = frame.scheduler.io_ack;
-        while (ack == frame.scheduler.io_ack) {
-            Frame.yield(status);
-        }
+        Frame.yield(status);
 
         // check if this was a cancel
         if (whole.num_operations > 0) {