QNetworkAccessCache: Rename first and last node

'oldest' and 'newest' to me make me thing of 'least recently inserted'
and 'most recently inserted', which is what they used to mean.
But now the expiration can be set per-request so the semantics don't
work anymore.
So, rename to 'nextExpiringNode' and 'lastExpiringNode'. Also rename the
node member elements "older" and "newer" to the more generic "previous"
and "next".

Change-Id: I582267d09c60c68396e4201e4a20185bbf0942e2
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>

src/network/access/qnetworkaccesscache.cpp

@@ -66,13 +66,14 @@ struct QNetworkAccessCache::Node
     QDateTime timestamp;
     QByteArray key;
 
-    Node *older, *newer;
+    Node *previous; // "previous" nodes expire "previous"ly (before us)
+    Node *next; // "next" nodes expire "next" (after us)
     CacheableObject *object;
 
     int useCount;
 
     Node()
-        : older(nullptr), newer(nullptr), object(nullptr), useCount(0)
+        : previous(nullptr), next(nullptr), object(nullptr), useCount(0)
     { }
 };
 
@@ -102,7 +103,7 @@ void QNetworkAccessCache::CacheableObject::setShareable(bool enable)
 }
 
 QNetworkAccessCache::QNetworkAccessCache()
-    : oldest(nullptr), newest(nullptr)
+    : firstExpiringNode(nullptr), lastExpiringNode(nullptr)
 {
 }
 
@@ -130,7 +131,7 @@ void QNetworkAccessCache::clear()
 
     timer.stop();
 
-    oldest = newest = nullptr;
+    firstExpiringNode = lastExpiringNode = nullptr;
 }
 
 /*!
@@ -143,58 +144,61 @@ void QNetworkAccessCache::linkEntry(const QByteArray &key)
     if (!node)
         return;
 
-    Q_ASSERT(node != oldest && node != newest);
-    Q_ASSERT(node->older == nullptr && node->newer == nullptr);
+    Q_ASSERT(node != firstExpiringNode && node != lastExpiringNode);
+    Q_ASSERT(node->previous == nullptr && node->next == nullptr);
     Q_ASSERT(node->useCount == 0);
 
 
     node->timestamp = QDateTime::currentDateTimeUtc().addSecs(node->object->expiryTimeoutSeconds);
 #ifdef QT_DEBUG
-    qDebug() << "QNetworkAccessCache case trying to insert=" <<QString::fromUtf8(key) << node->timestamp;
-    Node *current = newest;
+    qDebug() << "QNetworkAccessCache case trying to insert=" << QString::fromUtf8(key)
+             << node->timestamp;
+    Node *current = lastExpiringNode;
     while (current) {
-        qDebug() << "QNetworkAccessCache item=" << QString::fromUtf8(current->key) << current->timestamp << (current==newest? "newest":"") <<  (current==oldest? "oldest":"");
-        current = current->older;
+        qDebug() << "QNetworkAccessCache item=" << QString::fromUtf8(current->key)
+                 << current->timestamp << (current == lastExpiringNode ? "[last to expire]" : "")
+                 << (current == firstExpiringNode ? "[next to expire]" : "");
+        current = current->previous;
     }
 #endif
 
-    if (newest) {
-        Q_ASSERT(newest->newer == nullptr);
-        if (newest->timestamp < node->timestamp) {
-            // Insert as new newest.
-            node->older = newest;
-            newest->newer = node;
-            newest = node;
-            Q_ASSERT(newest->newer == nullptr);
+    if (lastExpiringNode) {
+        Q_ASSERT(lastExpiringNode->next == nullptr);
+        if (lastExpiringNode->timestamp < node->timestamp) {
+            // Insert as new last-to-expire node.
+            node->previous = lastExpiringNode;
+            lastExpiringNode->next = node;
+            lastExpiringNode = node;
+            Q_ASSERT(lastExpiringNode->next == nullptr);
         } else {
             // Insert in a sorted way, as different nodes might have had different expiryTimeoutSeconds set.
-            Node *current = newest;
-            while (current->older != nullptr && current->older->timestamp >= node->timestamp) {
-                current = current->older;
+            Node *current = lastExpiringNode;
+            while (current->previous != nullptr && current->previous->timestamp >= node->timestamp) {
+                current = current->previous;
             }
-            node->older = current->older;
-            if (node->older)
-                node->older->newer = node;
-            node->newer = current;
-            current->older = node;
-            if (node->older == nullptr) {
-                oldest = node;
-                Q_ASSERT(oldest->older == nullptr);
+            node->previous = current->previous;
+            if (node->previous)
+                node->previous->next = node;
+            node->next = current;
+            current->previous = node;
+            if (node->previous == nullptr) {
+                firstExpiringNode = node;
+                Q_ASSERT(firstExpiringNode->previous == nullptr);
             }
         }
     } else {
-        // no newest yet
-        newest = node;
+        // no current last-to-expire node
+        lastExpiringNode = node;
     }
-    if (!oldest) {
-        // there are no entries, so this is the oldest one too
-        oldest = node;
+    if (!firstExpiringNode) {
+        // there are no entries, so this is the next-to-expire too
+        firstExpiringNode = node;
     }
 }
 
 /*!
     Removes the entry pointed by \a key from the linked list.
-    Returns \c true if the entry removed was the oldest one.
+    Returns \c true if the entry removed was the next to expire.
  */
 bool QNetworkAccessCache::unlinkEntry(const QByteArray &key)
 {
@@ -202,30 +206,30 @@ bool QNetworkAccessCache::unlinkEntry(const QByteArray &key)
     if (!node)
         return false;
 
-    bool wasOldest = false;
-    if (node == oldest) {
-        oldest = node->newer;
-        wasOldest = true;
+    bool wasFirst = false;
+    if (node == firstExpiringNode) {
+        firstExpiringNode = node->next;
+        wasFirst = true;
     }
-    if (node == newest)
-        newest = node->older;
-    if (node->older)
-        node->older->newer = node->newer;
-    if (node->newer)
-        node->newer->older = node->older;
+    if (node == lastExpiringNode)
+        lastExpiringNode = node->previous;
+    if (node->previous)
+        node->previous->next = node->next;
+    if (node->next)
+        node->next->previous = node->previous;
 
-    node->newer = node->older = nullptr;
-    return wasOldest;
+    node->next = node->previous = nullptr;
+    return wasFirst;
 }
 
 void QNetworkAccessCache::updateTimer()
 {
     timer.stop();
 
-    if (!oldest)
+    if (!firstExpiringNode)
         return;
 
-    qint64 interval = QDateTime::currentDateTimeUtc().msecsTo(oldest->timestamp);
+    qint64 interval = QDateTime::currentDateTimeUtc().msecsTo(firstExpiringNode->timestamp);
     if (interval <= 0) {
         interval = 0;
     }
@@ -254,19 +258,19 @@ void QNetworkAccessCache::timerEvent(QTimerEvent *)
     // expire old items
     const QDateTime now = QDateTime::currentDateTimeUtc();
 
-    while (oldest && oldest->timestamp < now) {
-        Node *next = oldest->newer;
-        oldest->object->dispose();
-        hash.remove(oldest->key); // oldest gets deleted
-        delete oldest;
-        oldest = next;
+    while (firstExpiringNode && firstExpiringNode->timestamp < now) {
+        Node *next = firstExpiringNode->next;
+        firstExpiringNode->object->dispose();
+        hash.remove(firstExpiringNode->key); // `firstExpiringNode` gets deleted
+        delete firstExpiringNode;
+        firstExpiringNode = next;
     }
 
     // fixup the list
-    if (oldest)
-        oldest->older = nullptr;
+    if (firstExpiringNode)
+        firstExpiringNode->previous = nullptr;
     else
-        newest = nullptr;
+        lastExpiringNode = nullptr;
 
     updateTimer();
 }
@@ -323,10 +327,10 @@ QNetworkAccessCache::CacheableObject *QNetworkAccessCache::requestEntryNow(const
     }
 
     // entry not in use, let the caller have it
-    bool wasOldest = unlinkEntry(key);
+    bool wasNext = unlinkEntry(key);
     ++node->useCount;
 
-    if (wasOldest)
+    if (wasNext)
         updateTimer();
     return node->object;
 }
@@ -346,7 +350,7 @@ void QNetworkAccessCache::releaseEntry(const QByteArray &key)
         if (node->object->expires)
             linkEntry(key);
 
-        if (oldest == node)
+        if (firstExpiringNode == node)
             updateTimer();
     }
 }

src/network/access/qnetworkaccesscache_p.h

@@ -111,8 +111,8 @@ protected:
 private:
     // idea copied from qcache.h
     NodeHash hash;
-    Node *oldest;
-    Node *newest;
+    Node *firstExpiringNode;
+    Node *lastExpiringNode;
 
     QBasicTimer timer;