Speed up qsTr() by caching the translation context

qsTr() uses QFileInfo::baseName() to determine the translation
context from a URL.
The problem is that creating a QFileInfo object (and thus a
file engine object), as well as processing the URL to determine
the base name part, is very expensive.

By caching the last translation URL and context, qsTr() becomes
5x faster.
Only the most recent URL is cached, because a script's text will
be translated all at once (as the script is evaluated), so for
scripts with multiple translated strings only the first qsTr()
call will cause a cache miss.

The performance could be improved even further by getting rid of
the QFileInfo dependency altogether; created QTBUG-9939 for that
since it's a more risky change.

Task-number: QTBUG-6908
Reviewed-by: Olivier Goffart

2 files changed, 19 insertions, 2 deletions

diff --git a/src/script/api/qscriptengine.cpp b/src/script/api/qscriptengine.cpp
index 58c8d83..f732907 100644
--- a/src/script/api/qscriptengine.cpp
+++ b/src/script/api/qscriptengine.cpp
@@ -792,6 +792,7 @@ JSC::JSValue JSC_HOST_CALL functionQsTr(JSC::ExecState *exec, JSC::JSObject*, JS
     if ((args.size() > 2) && !args.at(2).isNumber())
         return JSC::throwError(exec, JSC::GeneralError, "qsTranslate(): third argument (n) must be a number");
 #ifndef QT_NO_QOBJECT
+    QScriptEnginePrivate *engine = scriptEngineFromExec(exec);
     JSC::UString context;
     // The first non-empty source URL in the call stack determines the translation context.
     {
@@ -799,7 +800,7 @@ JSC::JSValue JSC_HOST_CALL functionQsTr(JSC::ExecState *exec, JSC::JSObject*, JS
         while (frame) {
             if (frame->codeBlock() && frame->codeBlock()->source()
                 && !frame->codeBlock()->source()->url().isEmpty()) {
-                context = QFileInfo(frame->codeBlock()->source()->url()).baseName();
+                context = engine->translationContextFromUrl(frame->codeBlock()->source()->url());
                 break;
             }
             frame = frame->callerFrame()->removeHostCallFrameFlag();
@@ -921,6 +922,8 @@ QScriptEnginePrivate::QScriptEnginePrivate()
     activeAgent = 0;
     agentLineNumber = -1;
     processEventsInterval = -1;
+    cachedTranslationUrl = JSC::UString();
+    cachedTranslationContext = JSC::UString();
     JSC::setCurrentIdentifierTable(oldTable);
 }
 
@@ -3307,6 +3310,15 @@ bool QScriptEnginePrivate::hasDemarshalFunction(int type) const
     return info && (info->demarshal != 0);
 }
 
+JSC::UString QScriptEnginePrivate::translationContextFromUrl(const JSC::UString &url)
+{
+    if (url != cachedTranslationUrl) {
+        cachedTranslationContext = QFileInfo(url).baseName();
+        cachedTranslationUrl = url;
+    }
+    return cachedTranslationContext;
+}
+
 /*!
     \internal
 */
diff --git a/src/script/api/qscriptengine_p.h b/src/script/api/qscriptengine_p.h
index 5c2007f..fd47208 100644
--- a/src/script/api/qscriptengine_p.h
+++ b/src/script/api/qscriptengine_p.h
@@ -63,6 +63,7 @@
 #include "RegExpObject.h"
 #include "SourceProvider.h"
 #include "Structure.h"
+#include "UString.h"
 #include "JSGlobalObject.h"
 #include "JSValue.h"
 
@@ -73,7 +74,6 @@ namespace JSC
     typedef ExecState CallFrame;
     class JSCell;
     class JSGlobalObject;
-    class UString;
 }
 
 
@@ -298,6 +298,8 @@ public:
     static inline QScriptDeclarativeClass *declarativeClass(JSC::JSValue);
     static inline QScriptDeclarativeClass::Object *declarativeObject(JSC::JSValue);
 
+    JSC::UString translationContextFromUrl(const JSC::UString &);
+
 #ifndef QT_NO_QOBJECT
     JSC::JSValue newQObject(QObject *object,
         QScriptEngine::ValueOwnership ownership = QScriptEngine::QtOwnership,
@@ -367,6 +369,9 @@ public:
     QScriptValue abortResult;
     bool inEval;
 
+    JSC::UString cachedTranslationUrl;
+    JSC::UString cachedTranslationContext;
+
     QSet<QString> importedExtensions;
     QSet<QString> extensionsBeingImported;