Add shouldBeTerminatedOnParentExit parameter to Task.launch

Sources/Task.swift

@@ -390,10 +390,13 @@ extension Task {
 	/// - Parameters:
 	///   - standardInput: Data to stream to standard input of the launched process. If nil, stdin will
 	///                    be inherited from the parent process.
+	///   - shouldBeTerminatedOnParentExit: A flag to control whether the launched child process should be terminated
+	///                                     when the parent process exits. The default value is `false`.
 	///
 	/// - Returns: A producer that will launch the receiver when started, then send
 	///            `TaskEvent`s as execution proceeds.
-	public func launch(standardInput: SignalProducer<Data, NoError>? = nil) -> SignalProducer<TaskEvent<Data>, TaskError> {
+	public func launch(standardInput: SignalProducer<Data, NoError>? = nil,
+					   shouldBeTerminatedOnParentExit: Bool = false) -> SignalProducer<TaskEvent<Data>, TaskError> {
 		return SignalProducer { observer, lifetime in
 			let queue = DispatchQueue(label: self.description, attributes: [])
 			let group = Task.group
@@ -402,11 +405,13 @@ extension Task {
 			process.launchPath = self.launchPath
 			process.arguments = self.arguments
 
-			// This is for terminating subprocesses when the parent process exits.
-			// See https://github.com/Carthage/ReactiveTask/issues/3 for the details.
-			let selector = Selector(("setStartsNewProcessGroup:"))
-			if process.responds(to: selector) {
-				process.perform(selector, with: false as NSNumber)
+			if shouldBeTerminatedOnParentExit {
+				// This is for terminating subprocesses when the parent process exits.
+				// See https://github.com/Carthage/ReactiveTask/issues/3 for the details.
+				let selector = Selector(("setStartsNewProcessGroup:"))
+				if process.responds(to: selector) {
+					process.perform(selector, with: false as NSNumber)
+				}
 			}
 
 			if let cwd = self.workingDirectoryPath {