SynchronizedDictionaryAcquireWriteLock Method

Only a single thread can hold the write lock at any given time, and no other threads will be able to acquire either a read lock or a write lock until the write lock is released.

This method should always be used in combination with a ReleaseWriteLock method in the following manner:

dict.AcquireWriteLock();
try
{
    // access dictionary
}
finally
{
    dict.ReleaseWriteLock();
}

Reference