To serialize an SRB, use the SUSPEND and RESUME macros. The SUSPEND macro identifies the SRB that is to be suspended. In response to the SUSPEND macro, the system provides a token that identifies the SRB and invokes a user-provided exit routine. The exit routine must save the token and then decide whether to suspend the SRB or to allow it to continue running. The RESUME macro enables a program to request that the system resume execution of a suspended SRB or purge the SRB.