[Android] Allow JNI initialization on background thread

content/app/android/library_loader_hooks.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/public/app/android_library_loader_hooks.h"
 
 #include "base/android/base_jni_registrar.h"
 #include "base/android/jni_android.h"
 #include "base/android/jni_registrar.h"
 #include "base/android/jni_string.h"
@@ skipping 17 matching lines @@
 #include "net/android/net_jni_registrar.h"
 #include "ui/android/ui_jni_registrar.h"
 #include "ui/shell_dialogs/android/shell_dialogs_jni_registrar.h"
 
 namespace {
 base::AtExitManager* g_at_exit_manager = NULL;
 }
 
 namespace content {
 
-static jint LibraryLoadedOnMainThread(JNIEnv* env, jclass clazz,
-                                          jobjectArray init_command_line) {
+static jint LibraryLoaded(JNIEnv* env, jclass clazz,
+                          jobjectArray init_command_line) {
   InitNativeCommandLineFromJavaArray(env, init_command_line);
 
   CommandLine* command_line = CommandLine::ForCurrentProcess();
 
   if (command_line->HasSwitch(switches::kTraceStartup)) {
     base::debug::TraceLog::GetInstance()->SetEnabled(
         command_line->GetSwitchValueASCII(switches::kTraceStartup),
         base::debug::TraceLog::RECORD_UNTIL_FULL);
   }
 
   // Can only use event tracing after setting up the command line.
   TRACE_EVENT0("jni", "JNI_OnLoad continuation");
 
   // Note: because logging is setup here right after copying the command line
   // array from java to native up top of this method, any code that adds the
   // --enable-dcheck switch must do so on the Java side.
   logging::DcheckState dcheck_state =
       command_line->HasSwitch(switches::kEnableDCHECK) ?
       logging::ENABLE_DCHECK_FOR_NON_OFFICIAL_RELEASE_BUILDS :
       logging::DISABLE_DCHECK_FOR_NON_OFFICIAL_RELEASE_BUILDS;
   logging::InitLogging(NULL,

[joth, 2013/03/18 16:32:55]

internally this calls LoggingLock::Init which has the following rider:-

"LoggingLock::Init() should be called from the main thread before any logging"

that may not strictly mean 'the main' thread, more 'a single thread prior to
anything else using logging'. I can't tell from a quick look. Could you check,
and perhaps update that comment? (probably in a separate patch)

[aberent, 2013/03/18 18:44:54]

As I understand the code it does mean 'a single thread prior to anything else
using logging'. The reason is that this creates the pthread mutex used to
control access to the log. This can happen on any thread (pthreads doesn't even
know which thread is the main or UI thread), so long as it is completed before
anything attempts to use the mutex.

I will update this in a separate patch, but I need to check what to say about
Windows. Windows uses a Windows spinlock, and, for all I know, one may have to
create this on the UI thread.
On 2013/03/18 16:32:55, joth wrote:

                        logging::LOG_ONLY_TO_SYSTEM_DEBUG_LOG,
                        logging::DONT_LOCK_LOG_FILE,
                        logging::DELETE_OLD_LOG_FILE,
                        dcheck_state);
   // To view log output with IDs and timestamps use "adb logcat -v threadtime".
   logging::SetLogItems(false,    // Process ID
                        false,    // Thread ID
                        false,    // Timestamp
                        false);   // Tick count
   VLOG(0) << "Chromium logging enabled: level = " << logging::GetMinLogLevel()
@@ skipping 34 matching lines @@
 }
 
 bool RegisterLibraryLoaderEntryHook(JNIEnv* env) {
   // We need the AtExitManager to be created at the very beginning.
   g_at_exit_manager = new base::AtExitManager();
 
   return RegisterNativesImpl(env);
 }
 
 }  // namespace content