remove race from threadpool

src/ThreadPool.zig

@@ -291,6 +291,7 @@ pub noinline fn shutdown(self: *ThreadPool) void {
             // Wake up any threads sleeping on the idle_event.
             // TODO: I/O polling notification here.
             if (sync.idle > 0) self.idle_event.shutdown();
+            if (sync.spawned == 0) self.join_event.notify();
             return;
         });
     }
@@ -335,11 +336,8 @@ fn unregister(noalias self: *ThreadPool, noalias maybe_thread: ?*Thread) void {
 
 fn join(self: *ThreadPool) void {
     // Wait for the thread pool to be shutdown() then for all threads to enter a joinable state
-    var sync: Sync = @bitCast(self.sync.load(.monotonic));
-    if (!(sync.state == .shutdown and sync.spawned == 0)) {
-        self.join_event.wait();
-        sync = @bitCast(self.sync.load(.monotonic));
-    }
+    self.join_event.wait();
+    const sync: Sync = @bitCast(self.sync.load(.monotonic));
 
     assert(sync.state == .shutdown);
     assert(sync.spawned == 0);