Concurrency Mode in WCF
Concurrency is used to control number of threads active in an InstanceContext at any one time.
The following three concurrency modes are available:
•Single: Each instance context is allowed to have a maximum of one thread processing messages in the instance context at a time. Other threads wishing to use the same instance context must block until the original thread exits the instance context.
•Multiple: Each service instance can have multiple threads processing messages concurrently. The service implementation must be thread-safe to use this concurrency mode.
•Reentrant: Each service instance processes one message at a time, but accepts re-entrant operation calls. The service only accepts these calls when it is calling out through a WCF client object.