Circuit breaker uses a dedicated thread pool, separate from the server thread pool, to execute services for which a circuit breaker is configured. This thread pool is referred to as the circuit breaker thread pool. You can specify the minimum and maximum number of threads in the circuit breaker thread pool.

At run time, circuit breaker uses a thread from the circuit breaker thread pool to execute the requested service, passing the service invocation pipeline to the new thread. This thread is separate from the thread executing the calling service. The calling service waits for a response from the requested service. Circuit breaker returns the service results and then returns the thread to the circuit breaker thread pool. The calling service then proceeds with execution. If the requested service is configured to treat a time out as a failure event and the service does not execute to completion before the timeout period elapses, circuit breaker returns an exception to the calling service. If the Cancel thread on timeout property is set to false, circuit breaker orphans the thread. If the Cancel thread on timeout property is set to true, circuit breaker attempts to cancels the thread. If the thread cannot be canceled, circuit breaker abandons the thread.

Circuit breaker uses a separate thread pool because it decouples the thread that executes the calling service from the thread that executes the requested service. This decoupling allows the calling service to proceed with execution if the requested service does not complete before the timeout period elapses. As a result, failures can return quickly. For example, suppose that a circuit breaker is configured for a service that reads information from a database. If the database goes off line, an attempt to connect to the unavailable database and execute a query may wait a while before returning because network input/output operations typically cannot be interrupted. By using a separate thread for the requested service, the circuit breaker can abandon the thread and return an exception to the client without needing to wait for the input/output operation to complete.

You can configure the size of the circuit breaker thread pool by specifying the minimum and maximum number of threads for the pool. When the server starts, the circuit breaker thread pool initially contains the minimum number of threads. The server adds threads to the pool, as needed, until the pool contains the maximum number of allowed threads. If the pool reaches the maximum number of threads, before executing the next requested service with a configured circuit breaker, circuit breaker must wait for a thread to be returned to the pool.

The server provides server configuration parameters for specifying the minimum and maximum number of threads in the circuit breaker thread pool.

Use the server configuration properties to size the circuit breaker thread pool appropriately for your environment. Keep in mind that all services for which a circuit breaker is configured share the circuit breaker thread pool.