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VM: Fix memory leak during shutdown
The way runtime/platform/hashmap.h:HashMap was implemented so far did not allow deleting elements while iterating over the map. If one iterated like this HashMap::Entry* cursor = map.Start(); while (cursor != NULL) { if (cond) { map.Remove(cursor->key, cursor->hash); } cursor = map.Next(cursor); } Then the iteration `cursor` will skip elements. This is due to the fact that `HashMap::Remove()` is left-rotating elements in certain cases and `HashMap::Next()` will unconditionally advance to the next position in the backing store. PROBLEM IS: There was existing code which did remove elements while iterating over a HashMap. R=fschneider@google.com Review URL: https://codereview.chromium.org/2533303005 .
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@ -171,7 +171,7 @@ void TestSet(IntKeyHash hash, int size) {
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}
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UNIT_TEST_CASE(Set) {
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UNIT_TEST_CASE(HashMap_Basic) {
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TestSet(WordHash, 100);
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TestSet(Hash, 100);
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TestSet(CollisionHash1, 50);
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@ -180,4 +180,47 @@ UNIT_TEST_CASE(Set) {
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TestSet(CollisionHash4, 50);
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}
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UNIT_TEST_CASE(HashMap_RemoveDuringIteration) {
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class Utils {
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public:
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static bool MatchFun(void* key1, void* key2) { return key1 == key2; }
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static void* Key(intptr_t i) { return reinterpret_cast<void*>(i); }
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static void* Value(intptr_t i) { return reinterpret_cast<void*>(i); }
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static uint32_t HashCode(intptr_t key) { return 1; }
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};
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HashMap map(Utils::MatchFun, 8);
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// Add 6 (1, 1), ..., (6, 60) entries to the map all with a hashcode of 1
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// (i.e. have all keys have collinding hashcode).
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//
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// This causes the probing position in the hashmap to be 1 and open-addressing
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// with linear probing will fill in the slots towards the right
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// (i.e. from 1..6).
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for (intptr_t i = 1; i <= 6 /* avoid rehash at 7 */; i++) {
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HashMap::Entry* entry = map.Lookup(Utils::Key(i), Utils::HashCode(i), true);
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entry->value = Utils::Value(10 * i);
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}
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// Now we iterate over all elements and delete the current element. Since all
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// our entries have a colliding hashcode of 1, each deletion will cause all
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// following elements to be left-rotated by 1.
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intptr_t i = 0;
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HashMap::Entry* current = map.Start();
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while (current != NULL) {
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i++;
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EXPECT_EQ(Utils::Key(i), current->key);
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EXPECT_EQ(Utils::Value(10 * i), current->value);
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// Every 2nd element we keep to hit the left-rotation case only sometimes.
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if (i % 2 == 0) {
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current = map.Remove(current);
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} else {
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current = map.Next(current);
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}
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}
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EXPECT_EQ(6, i);
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}
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} // namespace dart
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@ -196,7 +196,8 @@ Dart_Handle ListeningSocketRegistry::CreateBindListen(Dart_Handle socket_object,
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}
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bool ListeningSocketRegistry::CloseOneSafe(OSSocket* os_socket) {
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bool ListeningSocketRegistry::CloseOneSafe(OSSocket* os_socket,
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bool update_hash_maps) {
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ASSERT(!mutex_->TryLock());
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ASSERT(os_socket != NULL);
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ASSERT(os_socket->ref_count > 0);
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@ -204,6 +205,7 @@ bool ListeningSocketRegistry::CloseOneSafe(OSSocket* os_socket) {
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if (os_socket->ref_count > 0) {
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return false;
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}
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if (update_hash_maps) {
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// We free the OS socket by removing it from two datastructures.
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RemoveByFd(os_socket->socketfd);
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@ -225,6 +227,7 @@ bool ListeningSocketRegistry::CloseOneSafe(OSSocket* os_socket) {
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// Remove element from the list which is not the first one.
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prev->next = os_socket->next;
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}
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}
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ASSERT(os_socket->ref_count == 0);
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delete os_socket;
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@ -234,9 +237,10 @@ bool ListeningSocketRegistry::CloseOneSafe(OSSocket* os_socket) {
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void ListeningSocketRegistry::CloseAllSafe() {
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MutexLocker ml(mutex_);
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for (HashMap::Entry* p = sockets_by_fd_.Start(); p != NULL;
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p = sockets_by_fd_.Next(p)) {
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CloseOneSafe(reinterpret_cast<OSSocket*>(p->value));
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for (HashMap::Entry* cursor = sockets_by_fd_.Start(); cursor != NULL;
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cursor = sockets_by_fd_.Next(cursor)) {
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CloseOneSafe(reinterpret_cast<OSSocket*>(cursor->value), false);
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}
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}
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@ -245,7 +249,7 @@ bool ListeningSocketRegistry::CloseSafe(intptr_t socketfd) {
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ASSERT(!mutex_->TryLock());
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OSSocket* os_socket = LookupByFd(socketfd);
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if (os_socket != NULL) {
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return CloseOneSafe(os_socket);
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return CloseOneSafe(os_socket, true);
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} else {
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// It should be impossible for the event handler to close something that
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// hasn't been created before.
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@ -469,7 +469,7 @@ class ListeningSocketRegistry {
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void InsertByFd(intptr_t fd, OSSocket* socket);
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void RemoveByFd(intptr_t fd);
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bool CloseOneSafe(OSSocket* os_socket);
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bool CloseOneSafe(OSSocket* os_socket, bool update_hash_maps);
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void CloseAllSafe();
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HashMap sockets_by_port_;
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@ -106,11 +106,27 @@ void HashMap::Remove(void* key, uint32_t hash) {
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// Clear the candidate which will not break searching the hash table.
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candidate->key = NULL;
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candidate->value = NULL;
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occupancy_--;
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}
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HashMap::Entry* HashMap::Remove(Entry* entry) {
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Remove(entry->key, entry->hash);
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// A key can only exist once in the map and we just removed `key`. This means
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// that either a left-rotation has happened (in which case `entry` points
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// already to the next element (in terms of iteration order)) or alternatively
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// we can use the normal `Next()` call to move in iteration order.
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if (entry->key != NULL) {
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// A left-rotation happened. `entry` points already to the next element in
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// iteration order.
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return entry;
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} else {
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return Next(entry);
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}
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}
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void HashMap::Clear(ClearFun clear) {
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// Mark all entries as empty.
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const Entry* end = map_end();
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@ -118,7 +134,6 @@ void HashMap::Clear(ClearFun clear) {
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if ((clear != NULL) && (p->key != NULL)) {
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clear(p->value);
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}
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p->value = NULL;
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p->key = NULL;
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}
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occupancy_ = 0;
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@ -61,8 +61,28 @@ class HashMap {
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Entry* Lookup(void* key, uint32_t hash, bool insert);
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// Removes the entry with matching key.
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//
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// WARNING: This method cannot be called while iterating a `HashMap`
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// otherwise the iteration might step over elements!
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void Remove(void* key, uint32_t hash);
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// Removes the entry and returns the next entry (in iteration order) after
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// this one.
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//
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// Usage instructions for removing elements during iteration:
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//
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// HashMap::Entry* current = map.Start();
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// while (current != NULL) {
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// ...
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// if (condition) {
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// current = map.Remove(current);
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// } else {
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// current = map.Next(current);
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// }
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// }
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//
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Entry* Remove(Entry* entry);
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// Empties the hash map (occupancy() == 0), and calls the function 'clear' on
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// each of the values if given.
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void Clear(ClearFun clear = NULL);
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