Teach ScriptRunner how to yield and post on loading task queue

Source/core/dom/ScriptRunner.cpp

Index: Source/core/dom/ScriptRunner.cpp
diff --git a/Source/core/dom/ScriptRunner.cpp b/Source/core/dom/ScriptRunner.cpp
index 44543abd54da0b4edd9e54bbfd7b30a2b3f8d947..9711fb83a18c40811cb6438fd69ea9d8c03a8cc7 100644
--- a/Source/core/dom/ScriptRunner.cpp
+++ b/Source/core/dom/ScriptRunner.cpp
@@ -30,12 +30,14 @@
 #include "core/dom/Element.h"
 #include "core/dom/ScriptLoader.h"
 #include "platform/heap/Handle.h"
+#include "platform/scheduler/Scheduler.h"
+#include "wtf/Functional.h"
 
 namespace blink {
 
 ScriptRunner::ScriptRunner(Document* document)
     : m_document(document)
-    , m_timer(this, &ScriptRunner::timerFired)
+    , m_executeScriptsTaskFactory(WTF::bind(&ScriptRunner::executeScripts, this))
 {
     ASSERT(document);
 }
@@ -77,13 +79,13 @@ void ScriptRunner::queueScriptForExecution(ScriptLoader* scriptLoader, Execution
 
 void ScriptRunner::suspend()
 {
-    m_timer.stop();
+    m_executeScriptsTaskFactory.cancel();
 }
 
 void ScriptRunner::resume()
 {
     if (hasPendingScripts())
-        m_timer.startOneShot(0, FROM_HERE);
+        Scheduler::shared()->postLoadingTask(FROM_HERE, m_executeScriptsTaskFactory.task());

[Sami, 2015/02/10 18:40:01]

Should we check whether we already have a callback posted? I think the timer
ends up doing that.

[alex clarke (OOO till 29th), 2015/02/18 18:28:20]

Both m_timer.startOneShot(0, FROM_HERE);  and  
Scheduler::shared()->postLoadingTask(FROM_HERE,
m_executeScriptsTaskFactory.task());  cancel any previously posted task.

 }
 
 void ScriptRunner::notifyScriptReady(ScriptLoader* scriptLoader, ExecutionType executionType)
@@ -99,7 +101,7 @@ void ScriptRunner::notifyScriptReady(ScriptLoader* scriptLoader, ExecutionType e
         ASSERT(!m_scriptsToExecuteInOrder.isEmpty());
         break;
     }
-    m_timer.startOneShot(0, FROM_HERE);
+    Scheduler::shared()->postLoadingTask(FROM_HERE, m_executeScriptsTaskFactory.task());

[Sami, 2015/02/10 18:40:01]

Ditto.

[alex clarke (OOO till 29th), 2015/02/18 18:28:20]

Acknowledged.

 }
 
 void ScriptRunner::notifyScriptLoadError(ScriptLoader* scriptLoader, ExecutionType executionType)
@@ -127,24 +129,28 @@ void ScriptRunner::movePendingAsyncScript(ScriptRunner* newRunner, ScriptLoader*
     }
 }
 
-void ScriptRunner::timerFired(Timer<ScriptRunner>* timer)
+void ScriptRunner::executeScripts()
 {
-    ASSERT_UNUSED(timer, timer == &m_timer);
-
     RefPtrWillBeRawPtr<Document> protect(m_document.get());
 
-    WillBeHeapVector<RawPtrWillBeMember<ScriptLoader> > scriptLoaders;
-    scriptLoaders.swap(m_scriptsToExecuteSoon);

[Sami, 2015/02/10 18:40:01]

Should we still take a snapshot of the pending scripts here? Otherwise we may
end up spinning here for much longer if shouldYield never ends returning true
and new scripts keep coming in. Also I don't think the ordering is preserved if
either m_scriptsToExecuteSoon or m_scriptsToExecuteInOrder get modified inside
the loop.

[alex clarke (OOO till 29th), 2015/02/18 18:28:20]

Good spot, that is a problem.
m_scriptsToExecuteSoon and m_scriptsToExecuteInOrder are only ever appended to. 
As long as we don't execute too many scripts we're good.

-
-    size_t numInOrderScriptsToExecute = 0;
-    for (; numInOrderScriptsToExecute < m_scriptsToExecuteInOrder.size() && m_scriptsToExecuteInOrder[numInOrderScriptsToExecute]->isReady(); ++numInOrderScriptsToExecute)
-        scriptLoaders.append(m_scriptsToExecuteInOrder[numInOrderScriptsToExecute]);
-    if (numInOrderScriptsToExecute)
-        m_scriptsToExecuteInOrder.remove(0, numInOrderScriptsToExecute);
+    while (!m_scriptsToExecuteSoon.isEmpty()) {
+        if (Scheduler::shared()->shouldYieldForHighPriorityWork()) {
+            Scheduler::shared()->postLoadingTask(FROM_HERE, m_executeScriptsTaskFactory.task());
+            return;
+        }
+        m_scriptsToExecuteSoon.takeFirst()->execute();
+        m_document->decrementLoadEventDelayCount();
+    }
 
-    size_t size = scriptLoaders.size();
-    for (size_t i = 0; i < size; ++i) {
-        scriptLoaders[i]->execute();
+    while (!m_scriptsToExecuteInOrder.isEmpty()) {
+        if (!m_scriptsToExecuteInOrder.first()->isReady()) {
+            break;
+        }
+        if (Scheduler::shared()->shouldYieldForHighPriorityWork()) {
+            Scheduler::shared()->postLoadingTask(FROM_HERE, m_executeScriptsTaskFactory.task());
+            return;
+        }
+        m_scriptsToExecuteInOrder.takeFirst()->execute();
         m_document->decrementLoadEventDelayCount();
     }
 }