fix: on some machines, deadlocks happened at launch

src/logic/BackgroundWork.swift

@@ -10,8 +10,6 @@ class BackgroundWork {
 
     // we cap concurrent tasks to .processorCount to avoid thread explosion on the .global queue
     static let globalSemaphore = DispatchSemaphore(value: ProcessInfo.processInfo.processorCount)
-    // AX calls may block for a long time. We use a big semaphore to avoid blocking the main thread in case the window server is busy
-    static let axCallsGlobalSemaphore = DispatchSemaphore(value: 100)
 
     // swift static variables are lazy; we artificially force the threads to init
     static func start() {
@@ -25,12 +23,12 @@ extension DispatchQueue {
         return DispatchQueue(label: label, target: .global(qos: qos.qosClass))
     }
 
-    func asyncWithCap(_ deadline: DispatchTime? = nil, semaphore: DispatchSemaphore = BackgroundWork.globalSemaphore, _ fn: @escaping () -> Void) {
+    func asyncWithCap(_ deadline: DispatchTime? = nil, _ fn: @escaping () -> Void) {
         let block = {
             fn()
-            semaphore.signal()
+            BackgroundWork.globalSemaphore.signal()
         }
-        semaphore.wait()
+        BackgroundWork.globalSemaphore.wait()
         if let deadline = deadline {
             asyncAfter(deadline: deadline, execute: block)
         } else {

src/logic/events/AccessibilityEvents.swift

@@ -7,15 +7,19 @@ func axObserverCallback(observer: AXObserver, element: AXUIElement, notification
 
 // if the window server is busy, it may not reply to AX calls. We retry right before the call times-out and returns a bogus value
 func retryAxCallUntilTimeout(_ fn: @escaping () throws -> Void, _ startTime: DispatchTime = DispatchTime.now()) {
-    BackgroundWork.axCallsQueue.asyncWithCap(semaphore: BackgroundWork.axCallsGlobalSemaphore) {
+    BackgroundWork.axCallsQueue.async {
+        retryAxCallUntilTimeout_(fn, startTime)
+    }
+}
+
+func retryAxCallUntilTimeout_(_ fn: @escaping () throws -> Void, _ startTime: DispatchTime = DispatchTime.now()) {
         do {
             try fn()
         } catch {
             let timePassedInSeconds = Double(DispatchTime.now().uptimeNanoseconds - startTime.uptimeNanoseconds) / 1_000_000_000
             if timePassedInSeconds < Double(AXUIElement.globalTimeoutInSeconds) {
-                BackgroundWork.axCallsQueue.asyncWithCap(.now() + .milliseconds(10), semaphore: BackgroundWork.axCallsGlobalSemaphore) {
+                BackgroundWork.axCallsQueue.asyncAfter(deadline: .now() + .milliseconds(10)) {
-                    retryAxCallUntilTimeout(fn, startTime)
+                retryAxCallUntilTimeout_(fn, startTime)
-                }
             }
         }
     }