public User GetUserFromId(int id)
{
try
{
this.readerWriterLock.EnterReadLock();
if (this.userCache.ContainsKey(id))
{
return(this.userCache[id]);
}
}
finally
{
this.readerWriterLock.ExitReadLock();
}
// We don't use a global lock while reading the user from the table
// We lock only the 'id' that we are trying to retrieve. For each id,
// we use a dummy lock object. This lock object is used to synchronize
// the threads attempting to read the same user object.
// The list of lock objects are stored in a dictionary.
// We first lock the dictionary and get/create a lock object for this id.
// Then we lock the lock object and check if another thread added the user to
// the cache already. If so, we return.
// Else we read it from the database, add the user to the user cache and exit.
object lockObject = null;
try
{
lock (this.userLockObjects)
{
if (!this.userLockObjects.ContainsKey(id))
{
this.userLockObjects.Add(id, new object());
}
lockObject = this.userLockObjects[id];
}
Monitor.Enter(lockObject);
if (this.userCache.ContainsKey(id))
{
return(this.userCache[id]);
}
User user = UserDbQuery.InternalGetUserFromId(id);
if (user == null)
{
return(null);
}
this.userCache.Add(id, user);
if (user.UserData.UserType != UserType.Group)
{
this.phoneUserCache.Add(user.UserData.PhoneNumber, user);
}
return(user);
}
finally
{
Monitor.Exit(lockObject);
lock (this.userLockObjects)
{
if (this.userLockObjects.ContainsKey(id))
{
this.userLockObjects.Remove(id);
}
}
}
}
public List <User> GetUsersFromPhones(List <string> phoneNumbers)
{
List <User> users = new List <User>();
List <string> notFoundPhoneNumbers = new List <string>();
Dictionary <int, User> addedUsers = new Dictionary <int, User>();
foreach (string phoneNumber in phoneNumbers)
{
try
{
this.readerWriterLock.EnterReadLock();
if (this.phoneUserCache.ContainsKey(phoneNumber))
{
User user = this.phoneUserCache[phoneNumber];
if (!addedUsers.ContainsKey(user.UserData.Id))
{
users.Add(this.phoneUserCache[phoneNumber]);
addedUsers.Add(user.UserData.Id, user);
}
}
else
{
notFoundPhoneNumbers.Add(phoneNumber);
}
}
finally
{
this.readerWriterLock.ExitReadLock();
}
}
List <User> notFoundUsers = UserDbQuery.InternalGetUsersFromPhones(notFoundPhoneNumbers);
foreach (User u in notFoundUsers)
{
if (!addedUsers.ContainsKey(u.UserData.Id))
{
users.Add(u);
addedUsers.Add(u.UserData.Id, u);
}
}
foreach (User user in notFoundUsers)
{
object lockObject = null;
try
{
lock (this.userLockObjects)
{
if (!this.userLockObjects.ContainsKey(user.UserData.Id))
{
this.userLockObjects.Add(user.UserData.Id, new object());
}
lockObject = this.userLockObjects[user.UserData.Id];
}
Monitor.Enter(lockObject);
if (this.userCache.ContainsKey(user.UserData.Id))
{
continue;
}
this.userCache.Add(user.UserData.Id, user);
this.phoneUserCache.Add(user.UserData.PhoneNumber, user);
}
finally
{
Monitor.Exit(lockObject);
lock (this.userLockObjects)
{
if (this.userLockObjects.ContainsKey(user.UserData.Id))
{
this.userLockObjects.Remove(user.UserData.Id);
}
}
}
}
return(users);
}
