Dealing with kernel waiting, sleeping, and delay mechanisms

The term sleeping in this section refers to a mechanism by which a task (on behalf of the running kernel code) voluntarily relaxes the processor, with the possibility of another task being scheduled. While simple sleeping would consist of a task sleeping and being awakened after a given duration (to passively delay an operation, for example), there are sleeping mechanisms based on external events (such as data availability). Simple sleeps are implemented in the kernel using dedicated APIs; waking up from such sleeps is implicit (handled by the kernel itself) after the duration expires. The other sleeping mechanism is conditioned on an event and the waking-up is explicit (another task must explicitly wake us up based on a condition, else we sleep forever) unless a sleeping timeout is specified. This mechanism is implemented in the kernel using the concept of wait queues. That said, both sleep APIs and wait queues implement...