[iossim] Work around pipe hang on some macs.

testing/iossim/iossim.mm

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 #import <Foundation/Foundation.h>
 #if defined(__MAC_10_12) && __MAC_OS_X_VERSION_MAX_ALLOWED >= __MAC_10_12
 #include <getopt.h>
 #include <string>
 
 namespace {
 
@@ skipping 71 matching lines @@
 
 - (void)setStandardError:(id)error {
   [_task setStandardError:error];
 }
 
 - (void)run {
   [_task launch];
   [_task waitUntilExit];
 }
 
+- (void)launch {
+  [_task launch];
+}
+
+- (void)waitUntilExit {
+  [_task waitUntilExit];
+}
+
 @end
 
 // Return array of available iOS runtime dictionaries.  Unavailable (old Xcode
 // versions) or other runtimes (tvOS, watchOS) are removed.
 NSArray* Runtimes(NSDictionary* simctl_list) {
   NSMutableArray* runtimes =
       [[simctl_list[@"runtimes"] mutableCopy] autorelease];
   for (NSDictionary* runtime in simctl_list[@"runtimes"]) {
     if (![runtime[@"identifier"]
             hasPrefix:@"com.apple.CoreSimulator.SimRuntime.iOS"] ||
@@ skipping 18 matching lines @@
   }
   return devicetypes;
 }
 
 // Get list of devices, runtimes, etc from sim_ctl.
 NSDictionary* GetSimulatorList() {
   XCRunTask* task = [[[XCRunTask alloc]
       initWithArguments:@[ @"simctl", @"list", @"-j" ]] autorelease];
   NSPipe* out = [NSPipe pipe];
   [task setStandardOutput:out];
-  [task run];
 
+  // In the rest of the this file we read from the pipe after -waitUntilExit
+  // (We normally wrap -launch and -waitUntilExit in one -run method).  However,
+  // on some swarming slaves this led to a hang on simctl's pipe.  Since the
+  // output of simctl is so instant, reading it before exit seems to work, and
+  // seems to avoid the hang.
+  [task launch];
   NSData* data = [[out fileHandleForReading] readDataToEndOfFile];
+  [task waitUntilExit];
+
   NSError* error = nil;
   return [NSJSONSerialization JSONObjectWithData:data
                                          options:kNilOptions
                                            error:&error];
 }
 
 // List supported runtimes and devices.
 void PrintSupportedDevices(NSDictionary* simctl_list) {
   printf("\niOS devices:\n");
   for (NSDictionary* type in Devices(simctl_list)) {
@@ skipping 1115 matching lines @@
   }
 
   // Note that this code is only executed if the simulator fails to start
   // because once the main run loop is started, only the delegate calling
   // exit() will end the program.
   [pool drain];
   return kExitFailure;
 }
 
 #endif