Revert "Install shutdown signal hooks as LifecycleTask (#88)" (#90)

motivation: start handlers should not actually be part of the initialization process, as it breaks composition between ServiceLifecycles

changes: This reverts commit dce53aa.

Author: tomerd

Sources/Lifecycle/Lifecycle.swift

@@ -183,7 +183,6 @@ public struct LifecycleShutdownHandler<State> {
 ///  By default, also install shutdown hooks based on `Signal` and backtraces.
 public struct ServiceLifecycle {
     private static let backtracesInstalled = AtomicBoolean(false)
-    private static let shutdownHooksInstalled = AtomicBoolean(false)
 
     private let configuration: Configuration
 
@@ -202,7 +201,6 @@ public struct ServiceLifecycle {
         self.underlying = ComponentLifecycle(label: self.configuration.label, logger: self.configuration.logger)
         // setup backtraces as soon as possible, so if we crash during setup we get a backtrace
         self.installBacktrace()
-        self.installShutdownHooks()
     }
 
     /// Starts the provided `LifecycleTask` array.
@@ -214,6 +212,7 @@ public struct ServiceLifecycle {
         guard self.underlying.idle else {
             preconditionFailure("already started")
         }
+        self.setupShutdownHook()
         self.underlying.start(on: self.configuration.callbackQueue, callback)
     }
 
@@ -223,6 +222,7 @@ public struct ServiceLifecycle {
         guard self.underlying.idle else {
             preconditionFailure("already started")
         }
+        self.setupShutdownHook()
         try self.underlying.startAndWait(on: self.configuration.callbackQueue)
     }
 
@@ -247,16 +247,9 @@ public struct ServiceLifecycle {
         }
     }
 
-    private func installShutdownHooks() {
-        if self.configuration.shutdownSignal != nil, ServiceLifecycle.shutdownHooksInstalled.compareAndSwap(expected: false, desired: true) {
-            self.register(label: "Shutdown hooks",
-                          start: .sync(self.installShutdownSignalHooks),
-                          shutdown: .none)
-        }
-    }
-
-    private func installShutdownSignalHooks() {
+    private func setupShutdownHook() {
         self.configuration.shutdownSignal?.forEach { signal in
+            self.log("setting up shutdown hook on \(signal)")
             let signalSource = ServiceLifecycle.trap(signal: signal, handler: { signal in
                 self.log("intercepted signal: \(signal)")
                 self.shutdown()