From 90fb2641458ca2de36f19ffc0d7becd4df5447fa Mon Sep 17 00:00:00 2001
From: Jari Vetoniemi <jari.vetoniemi@cloudef.pw>
Date: Sun, 5 Jan 2025 04:19:50 +0900
Subject: [PATCH] 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            | 8 +++++++-
 build.zig              | 2 +-
 src/coro/Scheduler.zig | 2 --
 src/coro/io.zig        | 5 +----
 4 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/bugs/31.zig b/bugs/31.zig
index 91f041c1..9a36d3e8 100644
--- a/bugs/31.zig
+++ b/bugs/31.zig
@@ -63,18 +63,24 @@ 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;
 }
 
 pub fn logger(index: usize, tmp: []usize) !void {
+    const State = struct {
+        var last: usize = 0;
+    };
     for (0..100) |i| {
         try delay(std.time.ns_per_ms * 200);
         tmp[index] = i + 1;
     }
     logInfo("{}. Finished\n", .{index + 1});
+    if (State.last != index) @panic("something went bonkers (1)");
+    State.last = index + 1;
 }
diff --git a/build.zig b/build.zig
index cf51892b..7837ea98 100644
--- a/build.zig
+++ b/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),
diff --git a/src/coro/Scheduler.zig b/src/coro/Scheduler.zig
index 4d590672..ff964b85 100644
--- a/src/coro/Scheduler.zig
+++ b/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| {
diff --git a/src/coro/io.zig b/src/coro/io.zig
index 5f508174..cdf79186 100644
--- a/src/coro/io.zig
+++ b/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) {