Event Control Blocks with CSL requests

The event control block (ECB) is an optional parameter within a CSL request that allows you to specify the address of the z/OS® ECB.

Most CSL requests allow an ECB to be specified. The ECB parameter is optional and specifies the address of the z/OS ECB. When a CSL request completes, the ECB specified by the ECB parameter is posted. If the parameter is not included, the requesting module does not receive control until the request completes.

If an ECB is specified, the invoker of the request must issue a WAIT (or equivalent) after receiving control from the request before the invoker uses or examines any data that is returned by this request (including the RETCODE and RSNCODE fields). If the WAIT is not issued, the data might be invalid.