From 0eed7ec9d51fe8c0dd22b72da0130ad9d31877d0 Mon Sep 17 00:00:00 2001
From: Timon Kruiper <timonkruiper@gmail.com>
Date: Wed, 23 Sep 2020 11:41:31 +0200
Subject: [PATCH 1/2] Eventloop: Fix deadlock in linux event loop
 implementation

A simple empty main with evented-io would not quit, because some
threads were still waiting to be resumed (by the os). The os.write to
the eventfd only wakes up one thread and thus there are multiple writes
needed to wake up all the other threads.
---
 lib/std/event/loop.zig | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

diff --git a/lib/std/event/loop.zig b/lib/std/event/loop.zig
index 2600b337b3..bc2eab3c90 100644
--- a/lib/std/event/loop.zig
+++ b/lib/std/event/loop.zig
@@ -687,9 +687,14 @@ pub const Loop = struct {
 
             switch (builtin.os.tag) {
                 .linux => {
-                    // writing 8 bytes to an eventfd cannot fail
-                    const amt = os.write(self.os_data.final_eventfd, &wakeup_bytes) catch unreachable;
-                    assert(amt == wakeup_bytes.len);
+                    // writing to the eventfd will only wake up one thread, thus multiple writes
+                    // are needed to wakeup all the threads
+                    var i: usize = 0;
+                    while (i < self.extra_threads.len + 1) : (i += 1) {
+                        // writing 8 bytes to an eventfd cannot fail
+                        const amt = os.write(self.os_data.final_eventfd, &wakeup_bytes) catch unreachable;
+                        assert(amt == wakeup_bytes.len);
+                    }
                     return;
                 },
                 .macosx, .freebsd, .netbsd, .dragonfly => {

From bbff6bd6754bbddef03e163406d09c748a479073 Mon Sep 17 00:00:00 2001
From: Timon Kruiper <timonkruiper@gmail.com>
Date: Wed, 23 Sep 2020 18:38:28 +0200
Subject: [PATCH 2/2] Eventloop: Enable basic event loop test, fixed by
 previous commit

Closes #4922
---
 lib/std/event/loop.zig | 5 -----
 1 file changed, 5 deletions(-)

diff --git a/lib/std/event/loop.zig b/lib/std/event/loop.zig
index bc2eab3c90..c547f50365 100644
--- a/lib/std/event/loop.zig
+++ b/lib/std/event/loop.zig
@@ -1257,11 +1257,6 @@ test "std.event.Loop - basic" {
     // https://github.com/ziglang/zig/issues/1908
     if (builtin.single_threaded) return error.SkipZigTest;
 
-    if (true) {
-        // https://github.com/ziglang/zig/issues/4922
-        return error.SkipZigTest;
-    }
-
     var loop: Loop = undefined;
     try loop.initMultiThreaded();
     defer loop.deinit();