web-threads: Create a single instance of WebThread for each blink thread.

content/child/blink_platform_impl.cc

Index: content/child/blink_platform_impl.cc
diff --git a/content/child/blink_platform_impl.cc b/content/child/blink_platform_impl.cc
index 0b8777cdc495c4766262d7604c9983b54c16640e..08f71634fa841f977d4f5ebfbb2c1db23c3932e6 100644
--- a/content/child/blink_platform_impl.cc
+++ b/content/child/blink_platform_impl.cc
@@ -13,7 +13,6 @@
 #include "base/files/file_path.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/singleton.h"
-#include "base/message_loop/message_loop.h"
 #include "base/metrics/histogram.h"
 #include "base/metrics/sparse_histogram.h"
 #include "base/process/process_metrics.h"
@@ -418,7 +417,7 @@ BlinkPlatformImpl::BlinkPlatformImpl()
       shared_timer_fire_time_(0.0),
       shared_timer_fire_time_was_set_while_suspended_(false),
       shared_timer_suspended_(0),
-      current_thread_slot_(&DestroyCurrentThread) {
+      current_thread_slot_() {
   InternalInit();
 }
 
@@ -429,7 +428,7 @@ BlinkPlatformImpl::BlinkPlatformImpl(
       shared_timer_fire_time_(0.0),
       shared_timer_fire_time_was_set_while_suspended_(false),
       shared_timer_suspended_(0),
-      current_thread_slot_(&DestroyCurrentThread) {
+      current_thread_slot_() {
   // TODO(alexclarke): Use c++11 delegated constructors when allowed.
   InternalInit();
 }
@@ -452,6 +451,11 @@ void BlinkPlatformImpl::InternalInit() {
   }
 }
 
+void BlinkPlatformImpl::UpdateWebThreadTLS(blink::WebThread* thread) {
+  DCHECK(!current_thread_slot_.Get());
+  current_thread_slot_.Set(thread);
+}
+
 BlinkPlatformImpl::~BlinkPlatformImpl() {
 }
 
@@ -499,23 +503,15 @@ bool BlinkPlatformImpl::isReservedIPAddress(
 }
 
 blink::WebThread* BlinkPlatformImpl::createThread(const char* name) {
-  return new WebThreadImpl(name);
+  WebThreadImpl* thread = new WebThreadImpl(name);
+  thread->TaskRunner()->PostTask(
+      FROM_HERE, base::Bind(&BlinkPlatformImpl::UpdateWebThreadTLS,
+                            base::Unretained(this), thread));
+  return thread;
 }
 
 blink::WebThread* BlinkPlatformImpl::currentThread() {
-  WebThreadImplForMessageLoop* thread =
-      static_cast<WebThreadImplForMessageLoop*>(current_thread_slot_.Get());
-  if (thread)
-    return (thread);
-
-  scoped_refptr<base::SingleThreadTaskRunner> task_runner =
-      MainTaskRunnerForCurrentThread();
-  if (!task_runner.get())
-    return NULL;
-
-  thread = new WebThreadImplForMessageLoop(task_runner);
-  current_thread_slot_.Set(thread);
-  return thread;
+  return static_cast<blink::WebThread*>(current_thread_slot_.Get());

[kinuko, 2015/02/27 09:54:27]

Hmm. By looking into the callsites in production code it doesn't look it's super
important to return a meaningful thread value here..

[sadrul, 2015/03/01 10:21:38]

it looks like it's used in some places to add task-observers to the thread (e.g.
MemoryCache, WebDevToolsAgentImpl). Do you think those are always called on the
main-thread?

[kinuko, 2015/03/02 06:08:17]

They belong to main thread afaik. (I'm ok to keep this one for now btw)

[sadrul, 2015/03/02 07:43:14]

If this is only called on the main thread, then indeed we can git rid of the TLS
from here (in fact, it may even be possible to not have
Platform::currentThread(), but I am not sure). I would like to look into that
separately though if that makes sense.

[kinuko, 2015/03/03 00:14:14]

This is not really true, it's also called on the worker thread (but only to
check if it's in unit tests or not) please see this comment:
https://codereview.chromium.org/959803003/#msg11

 }
 
 void BlinkPlatformImpl::yieldCurrentThread() {
@@ -1258,13 +1254,6 @@ BlinkPlatformImpl::MainTaskRunnerForCurrentThread() {
   }
 }
 
-// static
-void BlinkPlatformImpl::DestroyCurrentThread(void* thread) {
-  WebThreadImplForMessageLoop* impl =
-      static_cast<WebThreadImplForMessageLoop*>(thread);
-  delete impl;
-}
-
 WebString BlinkPlatformImpl::domCodeStringFromEnum(int dom_code) {
   return WebString::fromUTF8(ui::KeycodeConverter::DomCodeToCodeString(
       static_cast<ui::DomCode>(dom_code)));