Fix filtering of iOS Simulator logs per pid of new process

When application is restarted, the PID of the process is changed. So when showing device logs, we should change the pid when the printDeviceLog is called.
Spawn the process (`tail -f ...`) only one time, but change the PID whenever the method is called.

Author: rosen-vladimirov

lib/iphone-simulator-common.ts

@@ -9,6 +9,8 @@ import * as os from "os";
 import xcode = require("./xcode");
 let bplistParser = require("bplist-parser");
 let osenv = require("osenv");
+let isDeviceLogOperationStarted = false;
+let pid: string;
 
 export function getInstalledApplications(deviceId: string): IFuture<IApplication[]> {
 	return (() => {
@@ -38,37 +40,41 @@ export function getInstalledApplications(deviceId: string): IFuture<IApplication
 }
 
 export function printDeviceLog(deviceId: string, launchResult?: string): void {
-	let logFilePath = path.join(osenv.home(), "Library", "Logs", "CoreSimulator", deviceId, "system.log");
-	let pid: string;
 	if(launchResult) {
 		pid = launchResult.split(":")[1].trim();
 	}
-	let childProcess = require("child_process").spawn("tail", ['-f', '-n', '1', logFilePath]);
-	if (childProcess.stdout) {
-		childProcess.stdout.on("data", (data: NodeBuffer) => {
-			let dataAsString = data.toString();
-			if(pid) {
-				if (dataAsString.indexOf(`[${pid}]`) > -1) {
+
+	if(!isDeviceLogOperationStarted) {
+		let logFilePath = path.join(osenv.home(), "Library", "Logs", "CoreSimulator", deviceId, "system.log");
+		let childProcess = require("child_process").spawn("tail", ['-f', '-n', '1', logFilePath]);
+		if (childProcess.stdout) {
+			childProcess.stdout.on("data", (data: NodeBuffer) => {
+				let dataAsString = data.toString();
+				if(pid) {
+					if (dataAsString.indexOf(`[${pid}]`) > -1) {
+						process.stdout.write(dataAsString);
+					}
+				} else {
 					process.stdout.write(dataAsString);
 				}
-			} else {
-				process.stdout.write(dataAsString);
-			}
-		});
-	}
+			});
+		}
 
-	if (childProcess.stderr) {
-		childProcess.stderr.on("data", (data: string) => {
-			let dataAsString = data.toString();
-			if(pid) {
-				if (dataAsString.indexOf(`[${pid}]`) > -1) {
+		if (childProcess.stderr) {
+			childProcess.stderr.on("data", (data: string) => {
+				let dataAsString = data.toString();
+				if(pid) {
+					if (dataAsString.indexOf(`[${pid}]`) > -1) {
+						process.stdout.write(dataAsString);
+					}
+				} else {
 					process.stdout.write(dataAsString);
 				}
-			} else {
-				process.stdout.write(dataAsString);
-			}
-			process.stdout.write(data.toString());
-		});
+				process.stdout.write(data.toString());
+			});
+		}
+
+		isDeviceLogOperationStarted = true;
 	}
 }