QMimeDatabase: fix performance regression when using the internal XML

That XML was parsed over and over again, because the QMimeXMLProvider
was re-created instead of re-used.

Pick-to: 5.15
Change-Id: I07ff005d3f238afc1490b69a58cf4815e67d418c
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

3 files changed, 26 insertions, 3 deletions

diff --git a/src/corelib/mimetypes/qmimedatabase.cpp b/src/corelib/mimetypes/qmimedatabase.cpp
index aef4bc4a6b..7a9bf2880d 100644
--- a/src/corelib/mimetypes/qmimedatabase.cpp
+++ b/src/corelib/mimetypes/qmimedatabase.cpp
@@ -97,7 +97,7 @@ bool QMimeDatabasePrivate::shouldCheck()
 void QMimeDatabasePrivate::loadProviders()
 {
     // We use QStandardPaths every time to check if new files appeared
-    QStringList mimeDirs = QStandardPaths::locateAll(QStandardPaths::GenericDataLocation, QLatin1String("mime"), QStandardPaths::LocateDirectory);
+    const QStringList mimeDirs = QStandardPaths::locateAll(QStandardPaths::GenericDataLocation, QLatin1String("mime"), QStandardPaths::LocateDirectory);
     const auto fdoIterator = std::find_if(mimeDirs.constBegin(), mimeDirs.constEnd(), [](const QString &mimeDir) -> bool {
         return QFileInfo::exists(mimeDir + QStringLiteral("/packages/freedesktop.org.xml")); }
     );
@@ -108,12 +108,22 @@ void QMimeDatabasePrivate::loadProviders()
 
     if (QMimeXMLProvider::InternalDatabaseAvailable && fdoIterator == mimeDirs.constEnd()) {
         m_providers.reserve(mimeDirs.size() + 1);
-        m_providers.push_back(Providers::value_type(new QMimeXMLProvider(this, QMimeXMLProvider::InternalDatabase)));
+        // Check if we already have a provider for the InternalDatabase
+        const auto isInternal = [](const std::unique_ptr<QMimeProviderBase> &prov)
+        {
+            return prov && prov->isInternalDatabase();
+        };
+        const auto it = std::find_if(currentProviders.begin(), currentProviders.end(), isInternal);
+        if (it == currentProviders.end()) {
+            m_providers.push_back(Providers::value_type(new QMimeXMLProvider(this, QMimeXMLProvider::InternalDatabase)));
+        } else {
+            m_providers.push_back(std::move(*it));
+        }
     } else {
         m_providers.reserve(mimeDirs.size());
     }
 
-    for (const QString &mimeDir : qAsConst(mimeDirs)) {
+    for (const QString &mimeDir : mimeDirs) {
         const QString cacheFile = mimeDir + QStringLiteral("/mime.cache");
         QFileInfo fileInfo(cacheFile);
         // Check if we already have a provider for this dir
diff --git a/src/corelib/mimetypes/qmimeprovider.cpp b/src/corelib/mimetypes/qmimeprovider.cpp
index 6766a1bbec..7a6c522a9d 100644
--- a/src/corelib/mimetypes/qmimeprovider.cpp
+++ b/src/corelib/mimetypes/qmimeprovider.cpp
@@ -167,6 +167,11 @@ bool QMimeBinaryProvider::isValid()
     return m_cacheFile != nullptr;
 }
 
+bool QMimeBinaryProvider::isInternalDatabase() const
+{
+    return false;
+}
+
 // Position of the "list offsets" values, at the beginning of the mime.cache file
 enum {
     PosAliasListOffset = 4,
@@ -692,6 +697,11 @@ bool QMimeXMLProvider::isValid()
     return true;
 }
 
+bool QMimeXMLProvider::isInternalDatabase() const
+{
+    return m_directory == internalMimeFileName();
+}
+
 QMimeType QMimeXMLProvider::mimeTypeForName(const QString &name)
 {
     return m_nameMimeTypeMap.value(name);
diff --git a/src/corelib/mimetypes/qmimeprovider_p.h b/src/corelib/mimetypes/qmimeprovider_p.h
index 9c91903684..f9c8ef384c 100644
--- a/src/corelib/mimetypes/qmimeprovider_p.h
+++ b/src/corelib/mimetypes/qmimeprovider_p.h
@@ -71,6 +71,7 @@ public:
     virtual ~QMimeProviderBase() {}
 
     virtual bool isValid() = 0;
+    virtual bool isInternalDatabase() const = 0;
     virtual QMimeType mimeTypeForName(const QString &name) = 0;
     virtual void addFileNameMatches(const QString &fileName, QMimeGlobMatchResult &result) = 0;
     virtual void addParents(const QString &mime, QStringList &result) = 0;
@@ -98,6 +99,7 @@ public:
     virtual ~QMimeBinaryProvider();
 
     bool isValid() override;
+    bool isInternalDatabase() const override;
     QMimeType mimeTypeForName(const QString &name) override;
     void addFileNameMatches(const QString &fileName, QMimeGlobMatchResult &result) override;
     void addParents(const QString &mime, QStringList &result) override;
@@ -143,6 +145,7 @@ public:
     ~QMimeXMLProvider();
 
     bool isValid() override;
+    bool isInternalDatabase() const override;
     QMimeType mimeTypeForName(const QString &name) override;
     void addFileNameMatches(const QString &fileName, QMimeGlobMatchResult &result) override;
     void addParents(const QString &mime, QStringList &result) override;