Cache static compilation units

If we load the same file multiple times, we can re-use the old mapping.
In fact we may leak memory if we don't. The fact that we have to use a
mutex here is somewhat regrettable, but I haven't found a better way
of serializing access.

Task-number: QTBUG-89659
Pick-to: 5.15
Change-Id: Iaa44ac80faa5e95f30c05e950ab35083a8b0416b
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

3 files changed, 61 insertions, 12 deletions

diff --git a/src/qml/jsruntime/qv4compilationunitmapper.cpp b/src/qml/jsruntime/qv4compilationunitmapper.cpp
index 74f34a284d..f3e2b445d1 100644
--- a/src/qml/jsruntime/qv4compilationunitmapper.cpp
+++ b/src/qml/jsruntime/qv4compilationunitmapper.cpp
@@ -40,23 +40,69 @@
 #include "qv4compilationunitmapper_p.h"
 
 #include <private/qv4compileddata_p.h>
-#include <QFileInfo>
-#include <QDateTime>
-#include <QCoreApplication>
+#include <private/qv4executablecompilationunit_p.h>
+
+#include <QtCore/qdatetime.h>
+#include <QtCore/qmutex.h>
+#include <QtCore/qhash.h>
 
 QT_BEGIN_NAMESPACE
 
 using namespace QV4;
 
-CompilationUnitMapper::CompilationUnitMapper()
-    : dataPtr(nullptr)
+class StaticUnitCache
 {
+public:
+    StaticUnitCache() : m_lock(&s_mutex) {}
 
-}
+    CompilationUnitMapper get(const QString &file)
+    {
+        const auto it = s_staticUnits.constFind(file);
+        return it == s_staticUnits.constEnd() ? CompilationUnitMapper() : *it;
+    }
+
+    void set(const QString &file, const CompilationUnitMapper &staticUnit) {
+        s_staticUnits.insert(file, staticUnit);
+    }
+
+private:
+    QMutexLocker<QMutex> m_lock;
+
+    static QMutex s_mutex;
+
+    // We can copy the mappers around because they're all static, that is the dtors are noops.
+    static QHash<QString, CompilationUnitMapper> s_staticUnits;
+};
+
+QHash<QString, CompilationUnitMapper> StaticUnitCache::s_staticUnits;
+QMutex StaticUnitCache::s_mutex;
 
 CompilationUnitMapper::~CompilationUnitMapper()
 {
     close();
 }
 
+CompiledData::Unit *CompilationUnitMapper::get(
+        const QString &cacheFilePath, const QDateTime &sourceTimeStamp, QString *errorString)
+{
+    StaticUnitCache cache;
+
+    CompilationUnitMapper mapper = cache.get(cacheFilePath);
+    if (mapper.dataPtr) {
+        auto *unit = reinterpret_cast<CompiledData::Unit *>(mapper.dataPtr);
+        if (ExecutableCompilationUnit::verifyHeader(unit, sourceTimeStamp, errorString)) {
+            *this = mapper;
+            return unit;
+        }
+
+        return nullptr;
+    }
+
+    CompiledData::Unit *data = open(cacheFilePath, sourceTimeStamp, errorString);
+    if (data && (data->flags & CompiledData::Unit::StaticData))
+        cache.set(cacheFilePath, *this);
+
+    return data;
+}
+
 QT_END_NAMESPACE
diff --git a/src/qml/jsruntime/qv4compilationunitmapper_p.h b/src/qml/jsruntime/qv4compilationunitmapper_p.h
index 80f914c141..10ad0a6ede 100644
--- a/src/qml/jsruntime/qv4compilationunitmapper_p.h
+++ b/src/qml/jsruntime/qv4compilationunitmapper_p.h
@@ -65,17 +65,20 @@ struct Unit;
 class CompilationUnitMapper
 {
 public:
-    CompilationUnitMapper();
     ~CompilationUnitMapper();
 
-    CompiledData::Unit *open(const QString &cacheFilePath, const QDateTime &sourceTimeStamp, QString *errorString);
-    void close();
+    CompiledData::Unit *get(
+            const QString &cacheFilePath, const QDateTime &sourceTimeStamp, QString *errorString);
 
 private:
+    CompiledData::Unit *open(
+            const QString &cacheFilePath, const QDateTime &sourceTimeStamp, QString *errorString);
+    void close();
+
 #if defined(Q_OS_UNIX)
-    size_t length;
+    size_t length = 0;
 #endif
-    void *dataPtr;
+    void *dataPtr = nullptr;
 };
 
 }
diff --git a/src/qml/jsruntime/qv4executablecompilationunit.cpp b/src/qml/jsruntime/qv4executablecompilationunit.cpp
index 5aaec63a05..8ef8ae2221 100644
--- a/src/qml/jsruntime/qv4executablecompilationunit.cpp
+++ b/src/qml/jsruntime/qv4executablecompilationunit.cpp
@@ -764,7 +764,7 @@ bool ExecutableCompilationUnit::loadFromDisk(const QUrl &url, const QDateTime &s
 
     const QStringList cachePaths = { sourcePath + QLatin1Char('c'), localCacheFilePath(url) };
     for (const QString &cachePath : cachePaths) {
-        CompiledData::Unit *mappedUnit = cacheFile->open(cachePath, sourceTimeStamp, errorString);
+        CompiledData::Unit *mappedUnit = cacheFile->get(cachePath, sourceTimeStamp, errorString);
         if (!mappedUnit)
             continue;