From b0aa222e58d12bca6c5d6f51cf138fd82773d90b Mon Sep 17 00:00:00 2001
From: Mitchell Hashimoto <mitchell.hashimoto@gmail.com>
Date: Fri, 29 Apr 2022 19:20:47 -0700
Subject: [PATCH] libuv: Embed now uses a mutex + cond var

---
 src/libuv/Embed.zig | 44 +++++++++++++++++++++++++++++++++-----------
 1 file changed, 33 insertions(+), 11 deletions(-)

diff --git a/src/libuv/Embed.zig b/src/libuv/Embed.zig
index 75d2f172e..48ec09eac 100644
--- a/src/libuv/Embed.zig
+++ b/src/libuv/Embed.zig
@@ -10,15 +10,18 @@ const builtin = @import("builtin");
 const testing = std.testing;
 const Allocator = std.mem.Allocator;
 const Loop = @import("Loop.zig");
-const Sem = @import("Sem.zig");
 const Thread = @import("Thread.zig");
+const Mutex = @import("Mutex.zig");
+const Cond = @import("Cond.zig");
 
 const log = std.log.scoped(.libuv_embed);
 
 const BoolAtomic = std.atomic.Atomic(bool);
 
 loop: Loop,
-sem: Sem,
+mutex: Mutex,
+cond: Cond,
+ready: bool = false,
 terminate: BoolAtomic,
 sleeping: BoolAtomic,
 callback: fn () void,
@@ -29,7 +32,8 @@ thread: ?Thread,
 pub fn init(alloc: Allocator, loop: Loop, callback: fn () void) !Embed {
     return Embed{
         .loop = loop,
-        .sem = try Sem.init(alloc, 0),
+        .mutex = try Mutex.init(alloc),
+        .cond = try Cond.init(alloc),
         .terminate = BoolAtomic.init(false),
         .sleeping = BoolAtomic.init(false),
         .callback = callback,
@@ -40,7 +44,8 @@ pub fn init(alloc: Allocator, loop: Loop, callback: fn () void) !Embed {
 /// Deinit the embed struct. This will not automatically terminate
 /// the embed thread. You must call stop manually.
 pub fn deinit(self: *Embed, alloc: Allocator) void {
-    self.sem.deinit(alloc);
+    self.mutex.deinit(alloc);
+    self.cond.deinit(alloc);
     self.* = undefined;
 }
 
@@ -58,7 +63,7 @@ pub fn stop(self: *Embed) void {
     self.terminate.store(true, .SeqCst);
 
     // Post to the semaphore to ensure that any waits are processed.
-    self.sem.post();
+    self.cond.broadcast();
 }
 
 /// Wait for the thread backing the embedding to end.
@@ -72,9 +77,15 @@ pub fn join(self: *Embed) !void {
 /// loopRun runs the next tick of the libuv event loop. This should be
 /// called by the main loop thread as a result of callback making some
 /// signal. This should NOT be called from callback.
-pub fn loopRun(self: Embed) !void {
-    _ = try self.loop.run(.nowait);
-    self.sem.post();
+pub fn loopRun(self: *Embed) !void {
+    self.mutex.lock();
+    defer self.mutex.unlock();
+
+    if (self.ready) {
+        self.ready = false;
+        _ = try self.loop.run(.nowait);
+        self.cond.broadcast();
+    }
 }
 
 fn threadMain(self: *Embed) void {
@@ -98,7 +109,7 @@ fn threadMain(self: *Embed) void {
             // epoll
             .linux => {
                 var ev: [1]std.os.linux.epoll_event = undefined;
-                while (std.os.epoll_wait(fd, &ev, timeout) == -1) {}
+                _ = std.os.epoll_wait(fd, &ev, timeout);
             },
 
             // kqueue
@@ -129,8 +140,19 @@ fn threadMain(self: *Embed) void {
         // Call our trigger
         self.callback();
 
-        // Wait for libuv to run a tick
-        self.sem.wait();
+        // Wait for libuv to run a tick.
+        //
+        // NOTE: we use timedwait because I /believe/ there is a race here
+        // with gflw post event that sometimes causes it not to receive it.
+        // Therefore, if too much time passes, we just go back and loop
+        // through the poller.
+        //
+        // TODO: this is suboptimal for performance. There as to be a better
+        // way to do this.
+        self.mutex.lock();
+        defer self.mutex.unlock();
+        self.ready = true;
+        _ = self.cond.timedwait(self.mutex, 10 * 1000000);
     }
 }