Get rid of thread_darwin file.

This file has been causing problems for the build. ObjC was required for
a few methods because autoreleasepools are necessary on new threads if
those threads will be running objc code.

This CL introduces a workaround by using ObjC runtime C APIs to create
and drain autoreleasepools, but this comes with the cost of relying on
an internal API that may break on future OS/clang releases.

Bug: webrtc:9838
Change-Id: I18e765020c20c096c9ef8d80dfa82375ecb202ff
Reviewed-on: https://webrtc-review.googlesource.com/c/105301
Commit-Queue: Kári Helgason <kthelgason@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#25141}

rtc_base/BUILD.gn

@@ -692,29 +692,11 @@ rtc_static_library("rtc_base") {
   if (!build_with_mozilla) {
     public_deps += [ ":rtc_base_generic" ]
   }
-  if (is_win) {
+  if (is_win || is_mac || is_ios) {
     sources = [
       "noop.cc",
     ]
   }
-  if (is_ios || is_mac) {
-    sources = [
-      "noop.mm",
-    ]
-    public_deps += [ ":rtc_base_objc" ]
-  }
-}
-
-if (is_ios || is_mac) {
-  rtc_source_set("rtc_base_objc") {
-    sources = [
-      "thread_darwin.mm",
-    ]
-    deps = [
-      ":rtc_base_generic",
-    ]
-    visibility = [ ":rtc_base" ]
-  }
 }
 
 rtc_static_library("rtc_base_generic") {
@@ -894,6 +876,7 @@ rtc_static_library("rtc_base_generic") {
 
   if (is_ios || is_mac) {
     sources += [ "macifaddrs_converter.cc" ]
+    deps += [ "system:cocoa_threading" ]
   }
 
   if (rtc_use_x11) {

rtc_base/system/BUILD.gn

@@ -65,3 +65,15 @@ rtc_source_set("rtc_export") {
     "rtc_export.h",
   ]
 }
+
+if (is_mac || is_ios) {
+  rtc_source_set("cocoa_threading") {
+    sources = [
+      "cocoa_threading.h",
+      "cocoa_threading.mm",
+    ]
+    deps = [
+      "..:checks",
+    ]
+  }
+}

rtc_base/system/cocoa_threading.h

@@ -0,0 +1,24 @@
+/*
+ *  Copyright 2018 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef RTC_BASE_SYSTEM_COCOA_THREADING_H_
+#define RTC_BASE_SYSTEM_COCOA_THREADING_H_
+
+// If Cocoa is to be used on more than one thread, it must know that the
+// application is multithreaded.  Since it's possible to enter Cocoa code
+// from threads created by pthread_thread_create, Cocoa won't necessarily
+// be aware that the application is multithreaded.  Spawning an NSThread is
+// enough to get Cocoa to set up for multithreaded operation, so this is done
+// if necessary before pthread_thread_create spawns any threads.
+//
+// http://developer.apple.com/documentation/Cocoa/Conceptual/Multithreading/CreatingThreads/chapter_4_section_4.html
+void InitCocoaMultiThreading();
+
+#endif  // RTC_BASE_SYSTEM_COCOA_THREADING_H_

rtc_base/system/cocoa_threading.mm

@@ -0,0 +1,24 @@
+/*
+ *  Copyright 2018 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+#include "rtc_base/system/cocoa_threading.h"
+
+#import <Foundation/Foundation.h>
+
+#include "rtc_base/checks.h"
+
+void InitCocoaMultiThreading() {
+  static BOOL is_cocoa_multithreaded = [NSThread isMultiThreaded];
+  if (!is_cocoa_multithreaded) {
+    // +[NSObject class] is idempotent.
+    [NSThread detachNewThreadSelector:@selector(class) toTarget:[NSObject class] withObject:nil];
+    is_cocoa_multithreaded = YES;
+    RTC_DCHECK([NSThread isMultiThreaded]);
+  }
+}

rtc_base/thread.cc

@@ -33,6 +33,32 @@
 #include "rtc_base/timeutils.h"
 #include "rtc_base/trace_event.h"
 
+#if defined(WEBRTC_MAC)
+#include "rtc_base/system/cocoa_threading.h"
+/*
+ * These are forward-declarations for methods that are part of the
+ * ObjC runtime. They are declared in the private header objc-internal.h.
+ * These calls are what clang inserts when using @autoreleasepool in ObjC,
+ * but here they are used directly in order to keep this file C++.
+ * https://clang.llvm.org/docs/AutomaticReferenceCounting.html#runtime-support
+ */
+extern "C" {
+void* objc_autoreleasePoolPush(void);
+void objc_autoreleasePoolPop(void* pool);
+}
+
+namespace {
+class ScopedAutoReleasePool {
+ public:
+  ScopedAutoReleasePool() : pool_(objc_autoreleasePoolPush()) {}
+  ~ScopedAutoReleasePool() { objc_autoreleasePoolPop(pool_); }
+
+ private:
+  void* const pool_;
+};
+}  // namespace
+#endif
+
 namespace rtc {
 
 ThreadManager* ThreadManager::Instance() {
@@ -62,11 +88,12 @@ Thread* Thread::Current() {
 }
 
 #if defined(WEBRTC_POSIX)
-#if !defined(WEBRTC_MAC)
 ThreadManager::ThreadManager() : main_thread_ref_(CurrentThreadRef()) {
+#if defined(WEBRTC_MAC)
+  InitCocoaMultiThreading();
+#endif
   pthread_key_create(&key_, nullptr);
 }
-#endif
 
 Thread* ThreadManager::CurrentThread() {
   return static_cast<Thread*>(pthread_getspecific(key_));
@@ -301,7 +328,6 @@ void Thread::AssertBlockingIsAllowedOnCurrentThread() {
 }
 
 // static
-#if !defined(WEBRTC_MAC)
 #if defined(WEBRTC_WIN)
 DWORD WINAPI Thread::PreRun(LPVOID pv) {
 #else
@@ -310,6 +336,9 @@ void* Thread::PreRun(void* pv) {
   ThreadInit* init = static_cast<ThreadInit*>(pv);
   ThreadManager::Instance()->SetCurrentThread(init->thread);
   rtc::SetCurrentThreadName(init->thread->name_.c_str());
+#if defined(WEBRTC_MAC)
+  ScopedAutoReleasePool pool;
+#endif
   if (init->runnable) {
     init->runnable->Run(init->thread);
   } else {
@@ -323,7 +352,6 @@ void* Thread::PreRun(void* pv) {
   return nullptr;
 #endif
 }
-#endif
 
 void Thread::Run() {
   ProcessMessages(kForever);
@@ -486,9 +514,6 @@ void Thread::Clear(MessageHandler* phandler,
   ClearInternal(phandler, id, removed);
 }
 
-#if !defined(WEBRTC_MAC)
-// Note that these methods have a separate implementation for mac and ios
-// defined in webrtc/rtc_base/thread_darwin.mm.
 bool Thread::ProcessMessages(int cmsLoop) {
   // Using ProcessMessages with a custom clock for testing and a time greater
   // than 0 doesn't work, since it's not guaranteed to advance the custom
@@ -499,6 +524,9 @@ bool Thread::ProcessMessages(int cmsLoop) {
   int cmsNext = cmsLoop;
 
   while (true) {
+#if defined(WEBRTC_MAC)
+    ScopedAutoReleasePool pool;
+#endif
     Message msg;
     if (!Get(&msg, cmsNext))
       return !IsQuitting();
@@ -511,7 +539,6 @@ bool Thread::ProcessMessages(int cmsLoop) {
     }
   }
 }
-#endif
 
 bool Thread::WrapCurrentWithThreadManager(ThreadManager* thread_manager,
                                           bool need_synchronize_access) {

rtc_base/thread_darwin.mm

@@ -1,85 +0,0 @@
-/*
- *  Copyright 2017 The WebRTC Project Authors. All rights reserved.
- *
- *  Use of this source code is governed by a BSD-style license
- *  that can be found in the LICENSE file in the root of the source
- *  tree. An additional intellectual property rights grant can be found
- *  in the file PATENTS.  All contributing project authors may
- *  be found in the AUTHORS file in the root of the source tree.
- */
-
-#include "rtc_base/thread.h"
-
-#import <Foundation/Foundation.h>
-
-#include "rtc_base/platform_thread.h"
-#include "rtc_base/timeutils.h"  // for TimeAfter, TimeUntil
-
-/*
- * This file contains platform-specific implementations for several
- * methods in rtc::Thread.
- */
-
-namespace {
-void InitCocoaMultiThreading() {
-  if ([NSThread isMultiThreaded] == NO) {
-    // The sole purpose of this autorelease pool is to avoid a console
-    // message on Leopard that tells us we're autoreleasing the thread
-    // with no autorelease pool in place.
-    @autoreleasepool {
-      [NSThread detachNewThreadSelector:@selector(class)
-                               toTarget:[NSObject class]
-                             withObject:nil];
-    }
-  }
-
-  RTC_DCHECK([NSThread isMultiThreaded]);
-}
-}
-
-namespace rtc {
-
-ThreadManager::ThreadManager() : main_thread_ref_(CurrentThreadRef()) {
-  pthread_key_create(&key_, nullptr);
-  // This is necessary to alert the cocoa runtime of the fact that
-  // we are running in a multithreaded environment.
-  InitCocoaMultiThreading();
-}
-
-// static
-void* Thread::PreRun(void* pv) {
-  ThreadInit* init = static_cast<ThreadInit*>(pv);
-  ThreadManager::Instance()->SetCurrentThread(init->thread);
-  rtc::SetCurrentThreadName(init->thread->name_.c_str());
-  @autoreleasepool {
-    if (init->runnable) {
-      init->runnable->Run(init->thread);
-    } else {
-      init->thread->Run();
-    }
-  }
-  ThreadManager::Instance()->SetCurrentThread(nullptr);
-  delete init;
-  return nullptr;
-}
-
-bool Thread::ProcessMessages(int cmsLoop) {
-  int64_t msEnd = (kForever == cmsLoop) ? 0 : TimeAfter(cmsLoop);
-  int cmsNext = cmsLoop;
-
-  while (true) {
-    @autoreleasepool {
-      Message msg;
-      if (!Get(&msg, cmsNext))
-        return !IsQuitting();
-      Dispatch(&msg);
-
-      if (cmsLoop != kForever) {
-        cmsNext = static_cast<int>(TimeUntil(msEnd));
-        if (cmsNext < 0)
-          return true;
-      }
-    }
-  }
-}
-}  // namespace rtc