Minimizing wake lease acquisition with timeouts
Imagine that you have a Driver X which receives interrupts which can wake the system. The driver does some processing on the interrupt and passes an event on to Driver Y. We really only want Driver X to obtain a wake lease when an interrupt arrives which actually wakes the system or when Driver X observes the system starting to suspend within a timeout period of the last time we received an interrupt.
This strategy is not relevant when using Protocol Interlocks, since that strategy provides guarantees that Driver Y processed the event.
Refer to Taking Action on Suspend or Resume for how to observe
system suspend transitions. If Driver X receives an interrupt after it observes
suspend and before it observes resume then it should call
ActivityGovernor.AcquireWakeLease. Driver X can then ack the interrupt,
schedule a time to drop the wake lease, and pass the event on to Driver Y.
Driver X must keep a record of the last time an interrupt arrived. When Driver X observes the system suspending it must see if the current time is less than the last interrupt arrival time plus the timeout and if so, acquire a wake lease and hold it until the timeout for the last received interrupt arrives.
Using timeouts as a solution here is challenging because we must guess how long it will take Driver Y to receive the event and process it. Practically speaking, a good timeout value is even harder because often it won't be just the time in Driver Y we must account for, but also Component 1, Component 2, etc. Another challenge is picking a timeout that works on all system configurations Driver X runs on.