Fix concurrency issues

9 files changed, 276 insertions, 103 deletions

diff --git a/src/main/java/org/traccar/api/ExtendedObjectResource.java b/src/main/java/org/traccar/api/ExtendedObjectResource.java
index 007a7b1bd..9e554217e 100644
--- a/src/main/java/org/traccar/api/ExtendedObjectResource.java
+++ b/src/main/java/org/traccar/api/ExtendedObjectResource.java
@@ -55,8 +55,8 @@ public class ExtendedObjectResource<T extends BaseModel> extends BaseObjectResou
             Context.getPermissionsManager().checkDevice(getUserId(), deviceId);
             result.retainAll(manager.getDeviceItems(deviceId));
         }
-        return manager.getItems(result);
 
+        return manager.getItems(result);
     }
 
 }
diff --git a/src/main/java/org/traccar/database/BaseObjectManager.java b/src/main/java/org/traccar/database/BaseObjectManager.java
index 8bf9ef860..e274e5aba 100644
--- a/src/main/java/org/traccar/database/BaseObjectManager.java
+++ b/src/main/java/org/traccar/database/BaseObjectManager.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2017 Anton Tananaev (anton@traccar.org)
+ * Copyright 2017 - 2020 Anton Tananaev (anton@traccar.org)
  * Copyright 2017 Andrey Kunitsyn (andrey@traccar.org)
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
@@ -23,6 +23,8 @@ import java.util.LinkedList;
 import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.locks.ReadWriteLock;
+import java.util.concurrent.locks.ReentrantReadWriteLock;
 
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -32,6 +34,8 @@ public class BaseObjectManager<T extends BaseModel> {
 
     private static final Logger LOGGER = LoggerFactory.getLogger(BaseObjectManager.class);
 
+    private final ReadWriteLock lock = new ReentrantReadWriteLock();
+
     private final DataManager dataManager;
 
     private Map<Long, T> items;
@@ -43,6 +47,22 @@ public class BaseObjectManager<T extends BaseModel> {
         refreshItems();
     }
 
+    protected final void readLock() {
+        lock.readLock().lock();
+    }
+
+    protected final void readUnlock() {
+        lock.readLock().unlock();
+    }
+
+    protected final void writeLock() {
+        lock.writeLock().lock();
+    }
+
+    protected final void writeUnlock() {
+        lock.writeLock().unlock();
+    }
+
     protected final DataManager getDataManager() {
         return dataManager;
     }
@@ -52,12 +72,18 @@ public class BaseObjectManager<T extends BaseModel> {
     }
 
     public T getById(long itemId) {
-        return items.get(itemId);
+        try {
+            readLock();
+            return items.get(itemId);
+        } finally {
+            readUnlock();
+        }
     }
 
     public void refreshItems() {
         if (dataManager != null) {
             try {
+                writeLock();
                 Collection<T> databaseItems = dataManager.getObjects(baseClass);
                 if (items == null) {
                     items = new ConcurrentHashMap<>(databaseItems.size());
@@ -78,12 +104,19 @@ public class BaseObjectManager<T extends BaseModel> {
                 }
             } catch (SQLException error) {
                 LOGGER.warn("Error refreshing items", error);
+            } finally {
+                writeUnlock();
             }
         }
     }
 
     protected void addNewItem(T item) {
-        items.put(item.getId(), item);
+        try {
+            writeLock();
+            items.put(item.getId(), item);
+        } finally {
+            writeUnlock();
+        }
     }
 
     public void addItem(T item) throws SQLException {
@@ -92,7 +125,12 @@ public class BaseObjectManager<T extends BaseModel> {
     }
 
     protected void updateCachedItem(T item) {
-        items.put(item.getId(), item);
+        try {
+            writeLock();
+            items.put(item.getId(), item);
+        } finally {
+            writeUnlock();
+        }
     }
 
     public void updateItem(T item) throws SQLException {
@@ -101,7 +139,12 @@ public class BaseObjectManager<T extends BaseModel> {
     }
 
     protected void removeCachedItem(long itemId) {
-        items.remove(itemId);
+        try {
+            writeLock();
+            items.remove(itemId);
+        } finally {
+            writeUnlock();
+        }
     }
 
     public void removeItem(long itemId) throws SQLException {
@@ -121,7 +164,12 @@ public class BaseObjectManager<T extends BaseModel> {
     }
 
     public Set<Long> getAllItems() {
-        return items.keySet();
+        try {
+            readLock();
+            return items.keySet();
+        } finally {
+            readUnlock();
+        }
     }
 
 }
diff --git a/src/main/java/org/traccar/database/CommandsManager.java b/src/main/java/org/traccar/database/CommandsManager.java
index dc9512d9e..de6eeeba8 100644
--- a/src/main/java/org/traccar/database/CommandsManager.java
+++ b/src/main/java/org/traccar/database/CommandsManager.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2017 Anton Tananaev (anton@traccar.org)
+ * Copyright 2017 - 2020 Anton Tananaev (anton@traccar.org)
  * Copyright 2017 Andrey Kunitsyn (andrey@traccar.org)
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
@@ -142,14 +142,33 @@ public class CommandsManager  extends ExtendedObjectManager<Command> {
     }
 
     private Queue<Command> getDeviceQueue(long deviceId) {
-        if (!deviceQueues.containsKey(deviceId)) {
-            deviceQueues.put(deviceId, new ConcurrentLinkedQueue<Command>());
+        Queue<Command> deviceQueue;
+        try {
+            readLock();
+            deviceQueue = deviceQueues.get(deviceId);
+        } finally {
+            readUnlock();
+        }
+        if (deviceQueue != null) {
+            return deviceQueue;
+        } else {
+            try {
+                writeLock();
+                return deviceQueues.computeIfAbsent(deviceId, key -> new ConcurrentLinkedQueue<>());
+            } finally {
+                writeUnlock();
+            }
         }
-        return deviceQueues.get(deviceId);
     }
 
     public void sendQueuedCommands(ActiveDevice activeDevice) {
-        Queue<Command> deviceQueue = deviceQueues.get(activeDevice.getDeviceId());
+        Queue<Command> deviceQueue;
+        try {
+            readLock();
+            deviceQueue = deviceQueues.get(activeDevice.getDeviceId());
+        } finally {
+            readUnlock();
+        }
         if (deviceQueue != null) {
             Command command = deviceQueue.poll();
             while (command != null) {
diff --git a/src/main/java/org/traccar/database/DeviceManager.java b/src/main/java/org/traccar/database/DeviceManager.java
index fa95adeb2..fe17f7ced 100644
--- a/src/main/java/org/traccar/database/DeviceManager.java
+++ b/src/main/java/org/traccar/database/DeviceManager.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2016 - 2019 Anton Tananaev (anton@traccar.org)
+ * Copyright 2016 - 2020 Anton Tananaev (anton@traccar.org)
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -58,11 +58,16 @@ public class DeviceManager extends BaseObjectManager<Device> implements Identity
     public DeviceManager(DataManager dataManager) {
         super(dataManager, Device.class);
         this.config = Context.getConfig();
-        if (devicesByPhone == null) {
-            devicesByPhone = new ConcurrentHashMap<>();
-        }
-        if (devicesByUniqueId == null) {
-            devicesByUniqueId = new ConcurrentHashMap<>();
+        try {
+            writeLock();
+            if (devicesByPhone == null) {
+                devicesByPhone = new ConcurrentHashMap<>();
+            }
+            if (devicesByUniqueId == null) {
+                devicesByUniqueId = new ConcurrentHashMap<>();
+            }
+        } finally {
+            writeUnlock();
         }
         dataRefreshDelay = config.getLong("database.refreshDelay", DEFAULT_REFRESH_DELAY) * 1000;
         lookupGroupsAttribute = config.getBoolean("deviceManager.lookupGroupsAttribute");
@@ -108,11 +113,20 @@ public class DeviceManager extends BaseObjectManager<Device> implements Identity
 
     @Override
     public Device getByUniqueId(String uniqueId) throws SQLException {
-        boolean forceUpdate = !devicesByUniqueId.containsKey(uniqueId) && !config.getBoolean("database.ignoreUnknown");
-
+        boolean forceUpdate;
+        try {
+            readLock();
+            forceUpdate = !devicesByUniqueId.containsKey(uniqueId) && !config.getBoolean("database.ignoreUnknown");
+        } finally {
+            readUnlock();
+        }
         updateDeviceCache(forceUpdate);
-
-        return devicesByUniqueId.get(uniqueId);
+        try {
+            readLock();
+            return devicesByUniqueId.get(uniqueId);
+        } finally {
+            readUnlock();
+        }
     }
 
     @Override
@@ -134,7 +148,12 @@ public class DeviceManager extends BaseObjectManager<Device> implements Identity
     }
 
     public Device getDeviceByPhone(String phone) {
-        return devicesByPhone.get(phone);
+        try {
+            readLock();
+            return devicesByPhone.get(phone);
+        } finally {
+            readUnlock();
+        }
     }
 
     @Override
@@ -176,8 +195,7 @@ public class DeviceManager extends BaseObjectManager<Device> implements Identity
     }
 
     public Set<Long> getAllManagedItems(long userId) {
-        Set<Long> result = new HashSet<>();
-        result.addAll(getAllUserItems(userId));
+        Set<Long> result = new HashSet<>(getAllUserItems(userId));
         for (long managedUserId : Context.getUsersManager().getUserItems(userId)) {
             result.addAll(getAllUserItems(managedUserId));
         }
@@ -186,34 +204,68 @@ public class DeviceManager extends BaseObjectManager<Device> implements Identity
 
     @Override
     public Set<Long> getManagedItems(long userId) {
-        Set<Long> result = new HashSet<>();
-        result.addAll(getUserItems(userId));
+        Set<Long> result = new HashSet<>(getUserItems(userId));
         for (long managedUserId : Context.getUsersManager().getUserItems(userId)) {
             result.addAll(getUserItems(managedUserId));
         }
         return result;
     }
 
-    private void putUniqueDeviceId(Device device) {
-        if (devicesByUniqueId == null) {
-            devicesByUniqueId = new ConcurrentHashMap<>(getAllItems().size());
+    private void addByUniqueId(Device device) {
+        try {
+            writeLock();
+            if (devicesByUniqueId == null) {
+                devicesByUniqueId = new ConcurrentHashMap<>();
+            }
+            devicesByUniqueId.put(device.getUniqueId(), device);
+        } finally {
+            writeUnlock();
+        }
+    }
+
+    private void removeByUniqueId(String deviceUniqueId) {
+        try {
+            writeLock();
+            if (devicesByUniqueId != null) {
+                devicesByUniqueId.remove(deviceUniqueId);
+            }
+        } finally {
+            writeUnlock();
+        }
+    }
+
+    private void addByPhone(Device device) {
+        try {
+            writeLock();
+            if (devicesByPhone == null) {
+                devicesByPhone = new ConcurrentHashMap<>();
+            }
+            devicesByPhone.put(device.getPhone(), device);
+        } finally {
+            writeUnlock();
         }
-        devicesByUniqueId.put(device.getUniqueId(), device);
     }
 
-    private void putPhone(Device device) {
-        if (devicesByPhone == null) {
-            devicesByPhone = new ConcurrentHashMap<>(getAllItems().size());
+    private void removeByPhone(String phone) {
+        if (phone == null || phone.isEmpty()) {
+            return;
+        }
+        try {
+            writeLock();
+            if (devicesByPhone != null) {
+                devicesByPhone.remove(phone);
+            }
+        } finally {
+            writeUnlock();
         }
-        devicesByPhone.put(device.getPhone(), device);
     }
 
     @Override
     protected void addNewItem(Device device) {
         super.addNewItem(device);
-        putUniqueDeviceId(device);
+        addByUniqueId(device);
         if (device.getPhone() != null  && !device.getPhone().isEmpty()) {
-            putPhone(device);
+            addByPhone(device);
         }
         if (Context.getGeofenceManager() != null) {
             Position lastPosition = getLastPosition(device.getId());
@@ -234,18 +286,16 @@ public class DeviceManager extends BaseObjectManager<Device> implements Identity
         cachedDevice.setDisabled(device.getDisabled());
         cachedDevice.setAttributes(device.getAttributes());
         if (!device.getUniqueId().equals(cachedDevice.getUniqueId())) {
-            devicesByUniqueId.remove(cachedDevice.getUniqueId());
+            removeByUniqueId(cachedDevice.getUniqueId());
             cachedDevice.setUniqueId(device.getUniqueId());
-            putUniqueDeviceId(cachedDevice);
+            addByUniqueId(cachedDevice);
         }
         if (device.getPhone() != null && !device.getPhone().isEmpty()
                 && !device.getPhone().equals(cachedDevice.getPhone())) {
             String phone = cachedDevice.getPhone();
-            if (phone != null && !phone.isEmpty()) {
-                devicesByPhone.remove(phone);
-            }
+            removeByPhone(phone);
             cachedDevice.setPhone(device.getPhone());
-            putPhone(cachedDevice);
+            addByPhone(cachedDevice);
         }
     }
 
@@ -256,10 +306,8 @@ public class DeviceManager extends BaseObjectManager<Device> implements Identity
             String deviceUniqueId = cachedDevice.getUniqueId();
             String phone = cachedDevice.getPhone();
             super.removeCachedItem(deviceId);
-            devicesByUniqueId.remove(deviceUniqueId);
-            if (phone != null && !phone.isEmpty()) {
-                devicesByPhone.remove(phone);
-            }
+            removeByUniqueId(deviceUniqueId);
+            removeByPhone(phone);
         }
         positions.remove(deviceId);
     }
diff --git a/src/main/java/org/traccar/database/DriversManager.java b/src/main/java/org/traccar/database/DriversManager.java
index 930951460..d111cd643 100644
--- a/src/main/java/org/traccar/database/DriversManager.java
+++ b/src/main/java/org/traccar/database/DriversManager.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2017 Anton Tananaev (anton@traccar.org)
+ * Copyright 2017 - 2020 Anton Tananaev (anton@traccar.org)
  * Copyright 2017 Andrey Kunitsyn (andrey@traccar.org)
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
@@ -27,22 +27,44 @@ public class DriversManager extends ExtendedObjectManager<Driver> {
 
     public DriversManager(DataManager dataManager) {
         super(dataManager, Driver.class);
-        if (driversByUniqueId == null) {
-            driversByUniqueId = new ConcurrentHashMap<>();
+        try {
+            writeLock();
+            if (driversByUniqueId == null) {
+                driversByUniqueId = new ConcurrentHashMap<>();
+            }
+        } finally {
+            writeUnlock();
         }
     }
 
-    private void putUniqueDriverId(Driver driver) {
-        if (driversByUniqueId == null) {
-            driversByUniqueId = new ConcurrentHashMap<>(getAllItems().size());
+    private void addByUniqueId(Driver driver) {
+        try {
+            writeLock();
+            if (driversByUniqueId == null) {
+                driversByUniqueId = new ConcurrentHashMap<>();
+            }
+            driversByUniqueId.put(driver.getUniqueId(), driver);
+        } finally {
+            writeUnlock();
+        }
+    }
+
+    private void removeByUniqueId(String driverUniqueId) {
+        try {
+            writeLock();
+            if (driversByUniqueId == null) {
+                driversByUniqueId = new ConcurrentHashMap<>();
+            }
+            driversByUniqueId.remove(driverUniqueId);
+        } finally {
+            writeUnlock();
         }
-        driversByUniqueId.put(driver.getUniqueId(), driver);
     }
 
     @Override
     protected void addNewItem(Driver driver) {
         super.addNewItem(driver);
-        putUniqueDriverId(driver);
+        addByUniqueId(driver);
     }
 
     @Override
@@ -50,9 +72,9 @@ public class DriversManager extends ExtendedObjectManager<Driver> {
         Driver cachedDriver = getById(driver.getId());
         cachedDriver.setName(driver.getName());
         if (!driver.getUniqueId().equals(cachedDriver.getUniqueId())) {
-            driversByUniqueId.remove(cachedDriver.getUniqueId());
+            removeByUniqueId(cachedDriver.getUniqueId());
             cachedDriver.setUniqueId(driver.getUniqueId());
-            putUniqueDriverId(cachedDriver);
+            addByUniqueId(cachedDriver);
         }
         cachedDriver.setAttributes(driver.getAttributes());
     }
@@ -63,11 +85,16 @@ public class DriversManager extends ExtendedObjectManager<Driver> {
         if (cachedDriver != null) {
             String driverUniqueId = cachedDriver.getUniqueId();
             super.removeCachedItem(driverId);
-            driversByUniqueId.remove(driverUniqueId);
+            removeByUniqueId(driverUniqueId);
         }
     }
 
     public Driver getDriverByUniqueId(String uniqueId) {
-        return driversByUniqueId.get(uniqueId);
+        try {
+            readLock();
+            return driversByUniqueId.get(uniqueId);
+        } finally {
+            readUnlock();
+        }
     }
 }
diff --git a/src/main/java/org/traccar/database/ExtendedObjectManager.java b/src/main/java/org/traccar/database/ExtendedObjectManager.java
index ceb85b537..93e5820fb 100644
--- a/src/main/java/org/traccar/database/ExtendedObjectManager.java
+++ b/src/main/java/org/traccar/database/ExtendedObjectManager.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2017 Anton Tananaev (anton@traccar.org)
+ * Copyright 2017 - 2020 Anton Tananaev (anton@traccar.org)
  * Copyright 2017 Andrey Kunitsyn (andrey@traccar.org)
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
@@ -45,24 +45,45 @@ public abstract class ExtendedObjectManager<T extends BaseModel> extends SimpleO
     }
 
     public final Set<Long> getGroupItems(long groupId) {
-        if (!groupItems.containsKey(groupId)) {
-            groupItems.put(groupId, new HashSet<Long>());
+        try {
+            readLock();
+            Set<Long> result = groupItems.get(groupId);
+            if (result != null) {
+                return new HashSet<>(result);
+            } else {
+                return new HashSet<>();
+            }
+        } finally {
+            readUnlock();
         }
-        return groupItems.get(groupId);
     }
 
     public final Set<Long> getDeviceItems(long deviceId) {
-        if (!deviceItems.containsKey(deviceId)) {
-            deviceItems.put(deviceId, new HashSet<Long>());
+        try {
+            readLock();
+            Set<Long> result = deviceItems.get(deviceId);
+            if (result != null) {
+                return new HashSet<>(result);
+            } else {
+                return new HashSet<>();
+            }
+        } finally {
+            readUnlock();
         }
-        return deviceItems.get(deviceId);
     }
 
     public Set<Long> getAllDeviceItems(long deviceId) {
-        if (!deviceItemsWithGroups.containsKey(deviceId)) {
-            deviceItemsWithGroups.put(deviceId, new HashSet<Long>());
+        try {
+            readLock();
+            Set<Long> result = deviceItemsWithGroups.get(deviceId);
+            if (result != null) {
+                return new HashSet<>(result);
+            } else {
+                return new HashSet<>();
+            }
+        } finally {
+            readUnlock();
         }
-        return deviceItemsWithGroups.get(deviceId);
     }
 
     @Override
@@ -74,41 +95,48 @@ public abstract class ExtendedObjectManager<T extends BaseModel> extends SimpleO
     public void refreshExtendedPermissions() {
         if (getDataManager() != null) {
             try {
-
                 Collection<Permission> databaseGroupPermissions =
                         getDataManager().getPermissions(Group.class, getBaseClass());
 
-                groupItems.clear();
-                for (Permission groupPermission : databaseGroupPermissions) {
-                    getGroupItems(groupPermission.getOwnerId()).add(groupPermission.getPropertyId());
-                }
-
                 Collection<Permission> databaseDevicePermissions =
                         getDataManager().getPermissions(Device.class, getBaseClass());
 
+                writeLock();
+
+                groupItems.clear();
                 deviceItems.clear();
                 deviceItemsWithGroups.clear();
 
+                for (Permission groupPermission : databaseGroupPermissions) {
+                    groupItems
+                            .computeIfAbsent(groupPermission.getOwnerId(), key -> new HashSet<>())
+                            .add(groupPermission.getPropertyId());
+                }
+
                 for (Permission devicePermission : databaseDevicePermissions) {
-                    getDeviceItems(devicePermission.getOwnerId()).add(devicePermission.getPropertyId());
-                    getAllDeviceItems(devicePermission.getOwnerId()).add(devicePermission.getPropertyId());
+                    deviceItems
+                            .computeIfAbsent(devicePermission.getOwnerId(), key -> new HashSet<>())
+                            .add(devicePermission.getPropertyId());
+                    deviceItemsWithGroups
+                            .computeIfAbsent(devicePermission.getOwnerId(), key -> new HashSet<>())
+                            .add(devicePermission.getPropertyId());
                 }
 
                 for (Device device : Context.getDeviceManager().getAllDevices()) {
                     long groupId = device.getGroupId();
-                    while (groupId != 0) {
-                        getAllDeviceItems(device.getId()).addAll(getGroupItems(groupId));
+                    while (groupId > 0) {
+                        deviceItemsWithGroups
+                                .computeIfAbsent(device.getId(), key -> new HashSet<>())
+                                .addAll(groupItems.getOrDefault(groupId, new HashSet<>()));
                         Group group = Context.getGroupsManager().getById(groupId);
-                        if (group != null) {
-                            groupId = group.getGroupId();
-                        } else {
-                            groupId = 0;
-                        }
+                        groupId = group != null ? group.getGroupId() : 0;
                     }
                 }
 
             } catch (SQLException | ClassNotFoundException error) {
                 LOGGER.warn("Refresh permissions error", error);
+            } finally {
+                writeUnlock();
             }
         }
     }
diff --git a/src/main/java/org/traccar/database/GroupsManager.java b/src/main/java/org/traccar/database/GroupsManager.java
index d8404c614..81f1968aa 100644
--- a/src/main/java/org/traccar/database/GroupsManager.java
+++ b/src/main/java/org/traccar/database/GroupsManager.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2017 Anton Tananaev (anton@traccar.org)
+ * Copyright 2017 - 2020 Anton Tananaev (anton@traccar.org)
  * Copyright 2017 Andrey Kunitsyn (andrey@traccar.org)
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
@@ -95,8 +95,7 @@ public class GroupsManager extends BaseObjectManager<Group> implements Managable
 
     @Override
     public Set<Long> getManagedItems(long userId) {
-        Set<Long> result = new HashSet<>();
-        result.addAll(getUserItems(userId));
+        Set<Long> result = getUserItems(userId);
         for (long managedUserId : Context.getUsersManager().getUserItems(userId)) {
             result.addAll(getUserItems(managedUserId));
         }
diff --git a/src/main/java/org/traccar/database/SimpleObjectManager.java b/src/main/java/org/traccar/database/SimpleObjectManager.java
index 15dda4520..eb8284d4e 100644
--- a/src/main/java/org/traccar/database/SimpleObjectManager.java
+++ b/src/main/java/org/traccar/database/SimpleObjectManager.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2017 Anton Tananaev (anton@traccar.org)
+ * Copyright 2017 - 2020 Anton Tananaev (anton@traccar.org)
  * Copyright 2017 Andrey Kunitsyn (andrey@traccar.org)
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
@@ -42,16 +42,22 @@ public abstract class SimpleObjectManager<T extends BaseModel> extends BaseObjec
 
     @Override
     public final Set<Long> getUserItems(long userId) {
-        if (!userItems.containsKey(userId)) {
-            userItems.put(userId, new HashSet<Long>());
+        try {
+            readLock();
+            Set<Long> result = userItems.get(userId);
+            if (result != null) {
+                return new HashSet<>(result);
+            } else {
+                return new HashSet<>();
+            }
+        } finally {
+            readUnlock();
         }
-        return userItems.get(userId);
     }
 
     @Override
     public Set<Long> getManagedItems(long userId) {
-        Set<Long> result = new HashSet<>();
-        result.addAll(getUserItems(userId));
+        Set<Long> result = getUserItems(userId);
         for (long managedUserId : Context.getUsersManager().getUserItems(userId)) {
             result.addAll(getUserItems(managedUserId));
         }
@@ -71,16 +77,16 @@ public abstract class SimpleObjectManager<T extends BaseModel> extends BaseObjec
     public final void refreshUserItems() {
         if (getDataManager() != null) {
             try {
-                if (userItems != null) {
-                    userItems.clear();
-                } else {
-                    userItems = new ConcurrentHashMap<>();
-                }
+                writeLock();
+                userItems = new ConcurrentHashMap<>();
                 for (Permission permission : getDataManager().getPermissions(User.class, getBaseClass())) {
-                    getUserItems(permission.getOwnerId()).add(permission.getPropertyId());
+                    Set<Long> items = userItems.computeIfAbsent(permission.getOwnerId(), key -> new HashSet<>());
+                    items.add(permission.getPropertyId());
                 }
             } catch (SQLException | ClassNotFoundException error) {
                 LOGGER.warn("Error getting permissions", error);
+            } finally {
+                writeUnlock();
             }
         }
     }
diff --git a/src/main/java/org/traccar/database/UsersManager.java b/src/main/java/org/traccar/database/UsersManager.java
index 576a9e6c7..b741a85b6 100644
--- a/src/main/java/org/traccar/database/UsersManager.java
+++ b/src/main/java/org/traccar/database/UsersManager.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2017 Anton Tananaev (anton@traccar.org)
+ * Copyright 2017 - 2020 Anton Tananaev (anton@traccar.org)
  * Copyright 2017 Andrey Kunitsyn (andrey@traccar.org)
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
@@ -16,7 +16,6 @@
  */
 package org.traccar.database;
 
-import java.util.HashSet;
 import java.util.Map;
 import java.util.Set;
 import java.util.concurrent.ConcurrentHashMap;
@@ -73,8 +72,7 @@ public class UsersManager extends SimpleObjectManager<User> {
 
     @Override
     public Set<Long> getManagedItems(long userId) {
-        Set<Long> result = new HashSet<>();
-        result.addAll(getUserItems(userId));
+        Set<Long> result = getUserItems(userId);
         result.add(userId);
         return result;
     }