Android: Get rid of extra dup()s on launching child processes

content/browser/android/child_process_launcher_android.cc

 // 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.
 
 #include "content/browser/android/child_process_launcher_android.h"
 
 #include "base/android/jni_android.h"
 #include "base/android/jni_array.h"
 #include "base/logging.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 110 matching lines @@
   base::android::CheckException(env);
   jint* file_fds = env->GetIntArrayElements(j_file_fds.obj(), NULL);
   base::android::CheckException(env);
   ScopedJavaLocalRef<jbooleanArray> j_file_auto_close(
       env, env->NewBooleanArray(file_count));
   base::android::CheckException(env);
   jboolean* file_auto_close =
       env->GetBooleanArrayElements(j_file_auto_close.obj(), NULL);
   base::android::CheckException(env);
   for (size_t i = 0; i < file_count; ++i) {
-    // Owners of passed descriptors can outlive this function and we don't know
-    // when it is safe to close() them. So we pass dup()-ed FD and
-    // let ChildProcessLauncher in java take care of their lifetimes.
-    // TODO(morrita): Drop FileDescriptorInfo.mAutoClose on Java side.
-    file_auto_close[i] = true;  // This indicates ownership transfer.
     file_ids[i] = files_to_register->GetIDAt(i);
-    file_fds[i] = dup(files_to_register->GetFDAt(i));
+    file_fds[i] = files_to_register->GetFDAt(i);
     PCHECK(0 <= file_fds[i]);
+    file_auto_close[i] = files_to_register->OwnsFD(file_fds[i]);

[mdempsky, 2015/02/07 02:37:05]

OwnsFD and ReleaseFD seem like clunky APIs, but unfortunately I don't have a
better suggestion, so this seems okay.

Out of curiosity, why does ownership need to be transferred here at all?  Why
can't files_to_register continue to own its FDs, and set all of file_auto_close
to false?

+    if (file_auto_close[i])
+      ignore_result(files_to_register->ReleaseFD(file_fds[i]).release());
   }
   env->ReleaseIntArrayElements(j_file_ids.obj(), file_ids, 0);
   env->ReleaseIntArrayElements(j_file_fds.obj(), file_fds, 0);
   env->ReleaseBooleanArrayElements(j_file_auto_close.obj(), file_auto_close, 0);
 
   Java_ChildProcessLauncher_start(env,
       base::android::GetApplicationContext(),
       j_argv.obj(),
       child_process_id,
       j_file_ids.obj(),
@@ skipping 79 matching lines @@
 jboolean IsSingleProcess(JNIEnv* env, jclass clazz) {
   return base::CommandLine::ForCurrentProcess()->HasSwitch(
       switches::kSingleProcess);
 }
 
 bool RegisterChildProcessLauncher(JNIEnv* env) {
   return RegisterNativesImpl(env);
 }
 
 }  // namespace content