From f8f68067d7b822a6cb7aba4eaefdb32b1a4a7bc7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?C=C5=93ur?= <coeur@gmx.fr>
Date: Sun, 31 Dec 2023 22:17:31 +0100
Subject: [PATCH] perf: Don't poll every second for kevents (#6452)

* perf: Don't poll every second for kevents

* No need to alter properties in dealloc
---
 macosx/VDKQueue/VDKQueue.h  |  2 ++
 macosx/VDKQueue/VDKQueue.mm | 28 ++++++++++++++++------------
 2 files changed, 18 insertions(+), 12 deletions(-)

diff --git a/macosx/VDKQueue/VDKQueue.h b/macosx/VDKQueue/VDKQueue.h
index 1ee87b3db..ebfc912b2 100644
--- a/macosx/VDKQueue/VDKQueue.h
+++ b/macosx/VDKQueue/VDKQueue.h
@@ -86,6 +86,8 @@
 //
 //  - macOS 10.10+: DispatchSource API (makeFileSystemObjectSource)
 //  (https://developer.apple.com/documentation/dispatch/dispatchsource/2300040-makefilesystemobjectsource)
+//  "DispatchSource is just the Swift version of gcd dispatch sources"
+//  (https://github.com/bdkjones/VDKQueue/pull/22#issuecomment-1871623127)
 //
 //  Example: SFSMonitor (https://github.com/ClassicalDude/SFSMonitor)
 
diff --git a/macosx/VDKQueue/VDKQueue.mm b/macosx/VDKQueue/VDKQueue.mm
index ef6b0f81e..fe86122bc 100644
--- a/macosx/VDKQueue/VDKQueue.mm
+++ b/macosx/VDKQueue/VDKQueue.mm
@@ -39,8 +39,8 @@ NSString const* VDKQueueAccessRevocationNotification = @"VDKQueueAccessWasRevoke
 /// This is a simple model class used to hold info about each path we watch.
 @interface VDKQueuePathEntry : NSObject
 
-@property(atomic, copy) NSString* path;
-@property(atomic, assign) int watchedFD;
+@property(atomic, copy, readonly) NSString* path;
+@property(atomic, assign, readonly) int watchedFD;
 @property(atomic, assign) u_int subscriptionFlags;
 
 @end
@@ -69,7 +69,6 @@ NSString const* VDKQueueAccessRevocationNotification = @"VDKQueueAccessWasRevoke
     {
         close(_watchedFD);
     }
-    _watchedFD = -1;
 }
 
 @end
@@ -147,7 +146,6 @@ NSString const* VDKQueueAccessRevocationNotification = @"VDKQueueAccessWasRevoke
         {
             struct timespec nullts = { 0, 0 };
             struct kevent ev;
-
             EV_SET(&ev, pathEntry.watchedFD, EVFILT_VNODE, EV_ADD | EV_ENABLE | EV_CLEAR, flags, 0, (__bridge void*)pathEntry);
 
             pathEntry.subscriptionFlags = flags;
@@ -176,16 +174,13 @@ NSString const* VDKQueueAccessRevocationNotification = @"VDKQueueAccessWasRevoke
     NSThread.currentThread.name = @"VDKQueue";
 
     struct kevent ev;
-    // 1 second timeout. Should be longer, but we need this thread to exit when a kqueue is dealloced, so 1 second timeout is quite a while to wait.
-    const struct timespec timeout = { 1, 0 };
-    // So we don't have to risk accessing iVars when the thread is terminated.
     int const theFD = _coreQueueFD;
 
     NSMutableArray* notesToPost = [[NSMutableArray alloc] initWithCapacity:5];
 
     while (_keepWatcherThreadRunning)
     {
-        int n = kevent(theFD, NULL, 0, &ev, 1, &timeout);
+        int n = kevent(theFD, NULL, 0, &ev, 1, NULL);
         if (n <= 0 || ev.filter != EVFILT_VNODE || !ev.fflags)
         {
             continue;
@@ -294,6 +289,17 @@ NSString const* VDKQueueAccessRevocationNotification = @"VDKQueueAccessWasRevoke
     }
 }
 
+/// Shut down the thread that's scanning for kQueue events.
+- (void)shutdownWatcherThread
+{
+    _keepWatcherThreadRunning = NO;
+
+    // Trigger a custom event to stop the thread.
+    struct timespec nullts = { 0, 0 };
+    struct kevent stopEvent = { 0, EVFILT_USER, EV_ADD | EV_ONESHOT, NOTE_TRIGGER, 0, NULL };
+    kevent(_coreQueueFD, &stopEvent, 1, NULL, 0, &nullts);
+}
+
 - (void)removePath:(NSString*)aPath
 {
     if (!aPath)
@@ -310,8 +316,7 @@ NSString const* VDKQueueAccessRevocationNotification = @"VDKQueueAccessWasRevoke
 
         if (_watchedPathEntries.count == 0)
         {
-            // Shut down the thread that's scanning for kQueue events.
-            _keepWatcherThreadRunning = NO;
+            [self shutdownWatcherThread];
         }
     }
 }
@@ -323,8 +328,7 @@ NSString const* VDKQueueAccessRevocationNotification = @"VDKQueueAccessWasRevoke
         // Close all the open file descriptors for files we're watching.
         [_watchedPathEntries removeAllObjects];
 
-        // Shut down the thread that's scanning for kQueue events.
-        _keepWatcherThreadRunning = NO;
+        [self shutdownWatcherThread];
     }
 }