QMimeProvider: fix quadratic loop

Calling QMutableListIterator::remove() in a loop constitutes quadratic
behavior (O(N) function called O(N) times).

Fix by splitting the loop, simplifying it by sharing conditions, and
using std::remove_if(), which is linear.

Removes one more use of mutable Java iterators.

Change-Id: I88bde414777b50996e546bc8cb238619ea4fb645
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: David Faure <david.faure@kdab.com>

1 files changed, 14 insertions, 12 deletions

diff --git a/src/corelib/mimetypes/qmimeprovider.cpp b/src/corelib/mimetypes/qmimeprovider.cpp
index e72f9a30d0..e25eb4272d 100644
--- a/src/corelib/mimetypes/qmimeprovider.cpp
+++ b/src/corelib/mimetypes/qmimeprovider.cpp
@@ -217,22 +217,24 @@ bool QMimeBinaryProvider::isValid()
 bool QMimeBinaryProvider::CacheFileList::checkCacheChanged()
 {
     bool somethingChanged = false;
-    QMutableListIterator<CacheFile *> it(*this);
-    while (it.hasNext()) {
-        CacheFile *cacheFile = it.next();
+    for (CacheFile *cacheFile : qAsConst(*this)) {
         QFileInfo fileInfo(cacheFile->file);
-        if (!fileInfo.exists()) { // This can't happen by just running update-mime-database. But the user could use rm -rf :-)
-            delete cacheFile;
-            it.remove();
-            somethingChanged = true;
-        } else if (fileInfo.lastModified() > cacheFile->m_mtime) {
-            if (!cacheFile->reload()) {
-                delete cacheFile;
-                it.remove();
-            }
+        if (!fileInfo.exists() || fileInfo.lastModified() > cacheFile->m_mtime) {
+            // Deletion can't happen by just running update-mime-database.
+            // But the user could use rm -rf :-)
+            cacheFile->reload(); // will mark itself as invalid on failure
             somethingChanged = true;
         }
     }
+    if (somethingChanged) {
+        auto deleteIfNoLongerValid = [](CacheFile *cacheFile) -> bool {
+            const bool invalid = !cacheFile->isValid();
+            if (invalid)
+                delete cacheFile;
+            return invalid;
+        };
+        erase(std::remove_if(begin(), end(), deleteIfNoLongerValid), end());
+    }
     return somethingChanged;
 }