From f02e83b80bab262ab012ab85612fad9ffeeb1880 Mon Sep 17 00:00:00 2001
From: Josh Bleecher Snyder <josharian@gmail.com>
Date: Mon, 12 Dec 2022 17:10:45 -0800
Subject: [PATCH] switch from runloops to dispatch queues

This simplifies the code and removes a runloop-related deprecation.

Fixes #212
---
 watcher_fsevents_cgo.go | 57 ++++++++---------------------------------
 1 file changed, 11 insertions(+), 46 deletions(-)

diff --git a/watcher_fsevents_cgo.go b/watcher_fsevents_cgo.go
index b0b5a4a..7cf7d71 100644
--- a/watcher_fsevents_cgo.go
+++ b/watcher_fsevents_cgo.go
@@ -9,10 +9,8 @@ package notify
 
 /*
 #include <CoreServices/CoreServices.h>
+#include <dispatch/dispatch.h>
 
-typedef void (*CFRunLoopPerformCallBack)(void*);
-
-void gosource(void *);
 void gostream(uintptr_t, uintptr_t, size_t, uintptr_t, uintptr_t, uintptr_t);
 
 static FSEventStreamRef EventStreamCreate(FSEventStreamContext * context, uintptr_t info, CFArrayRef paths, FSEventStreamEventId since, CFTimeInterval latency, FSEventStreamCreateFlags flags) {
@@ -27,7 +25,6 @@ import "C"
 import (
 	"errors"
 	"os"
-	"runtime"
 	"sync"
 	"sync/atomic"
 	"unsafe"
@@ -42,16 +39,11 @@ var (
 	since   = uint64(C.FSEventsGetCurrentEventId())
 )
 
-var runloop C.CFRunLoopRef // global runloop which all streams are registered with
-var wg sync.WaitGroup      // used to wait until the runloop starts
-
-// source is used for synchronization purposes - it signals when runloop has
-// started and is ready via the wg. It also serves purpose of a dummy source,
-// thanks to it the runloop does not return as it also has at least one source
-// registered.
-var source = C.CFRunLoopSourceCreate(C.kCFAllocatorDefault, 0, &C.CFRunLoopSourceContext{
-	perform: (C.CFRunLoopPerformCallBack)(C.gosource),
-})
+// global dispatch queue which all streams are registered with
+var q C.dispatch_queue_t = C.dispatch_queue_create(
+	C.CString("com.github.rjeczalik.notify"),
+	(C.dispatch_queue_attr_t)(C.DISPATCH_QUEUE_SERIAL),
+)
 
 // Errors returned when FSEvents functions fail.
 var (
@@ -59,28 +51,6 @@ var (
 	errStart  = os.NewSyscallError("FSEventStreamStart", errors.New("false"))
 )
 
-// initializes the global runloop and ensures any created stream awaits its
-// readiness.
-func init() {
-	wg.Add(1)
-	go func() {
-		// There is exactly one run loop per thread. Lock this goroutine to its
-		// thread to ensure that it's not rescheduled on a different thread while
-		// setting up the run loop.
-		runtime.LockOSThread()
-		runloop = C.CFRunLoopGetCurrent()
-		C.CFRunLoopAddSource(runloop, source, C.kCFRunLoopDefaultMode)
-		C.CFRunLoopRun()
-		panic("runloop has just unexpectedly stopped")
-	}()
-	C.CFRunLoopSourceSignal(source)
-}
-
-//export gosource
-func gosource(unsafe.Pointer) {
-	wg.Done()
-}
-
 //export gostream
 func gostream(_, info uintptr, n C.size_t, paths, flags, ids uintptr) {
 	const (
@@ -143,8 +113,7 @@ func (r *streamFuncRegistry) delete(id uintptr) {
 	delete(r.m, id)
 }
 
-// Stream represents single watch-point which listens for events scheduled by
-// the global runloop.
+// Stream represents a single watch-point which listens for events scheduled on the global dispatch queue.
 type stream struct {
 	path string
 	ref  C.FSEventStreamRef
@@ -160,13 +129,12 @@ func newStream(path string, fn streamFunc) *stream {
 	}
 }
 
-// Start creates a FSEventStream for the given path and schedules it with
-// global runloop. It's a nop if the stream was already started.
+// Start creates a FSEventStream for the given path and schedules on the global dispatch queue.
+// It's a nop if the stream was already started.
 func (s *stream) Start() error {
 	if s.ref != nilstream {
 		return nil
 	}
-	wg.Wait()
 	p := C.CFStringCreateWithCStringNoCopy(C.kCFAllocatorDefault, C.CString(s.path), C.kCFStringEncodingUTF8, C.kCFAllocatorDefault)
 	path := C.CFArrayCreate(C.kCFAllocatorDefault, (*unsafe.Pointer)(unsafe.Pointer(&p)), 1, nil)
 	ctx := C.FSEventStreamContext{}
@@ -174,25 +142,22 @@ func (s *stream) Start() error {
 	if ref == nilstream {
 		return errCreate
 	}
-	C.FSEventStreamScheduleWithRunLoop(ref, runloop, C.kCFRunLoopDefaultMode)
+	C.FSEventStreamSetDispatchQueue(ref, q)
 	if C.FSEventStreamStart(ref) == C.Boolean(0) {
 		C.FSEventStreamInvalidate(ref)
 		return errStart
 	}
-	C.CFRunLoopWakeUp(runloop)
 	s.ref = ref
 	return nil
 }
 
-// Stop stops underlying FSEventStream and unregisters it from global runloop.
+// Stop stops underlying FSEventStream and unregisters it from the global dispatch queue.
 func (s *stream) Stop() {
 	if s.ref == nilstream {
 		return
 	}
-	wg.Wait()
 	C.FSEventStreamStop(s.ref)
 	C.FSEventStreamInvalidate(s.ref)
-	C.CFRunLoopWakeUp(runloop)
 	s.ref = nilstream
 	streamFuncs.delete(s.info)
 }