Another interesting use of message queues is shown in Figure 15-10. Here, a task (the server) is used to monitor error conditions that are sent to it by other tasks or ISRs (clients). For example, a client detects whether the RPM of the rotating wheel has been exceeded, another client detects whether an over-temperature exists, and yet another client detects that a user pressed a shutdown button. When the clients detect error conditions, they send a message through the message queue. The message sent indicates the error detected, which threshold was exceeded, the error code that is associated with error conditions, or even suggests the address of a function that will handle the error, and more.
Figure 15-10 Clients and Servers