Hands-On System Programming with Linux

Priority inversion

Let's visualize an application that contains three threads; one of them is a high priority thread (let's calls it thread A with priority 90), the other is a low priority thread (let's calls it thread B with priority 10) and finally a medium priority thread, C. (The priority range for the SCHED_FIFO scheduling policy is 1 to 99, with 99 being the highest possible priority; more on this in a later chapter.) So, we can imagine that we have these three threads within a process at differing priorities:

• Thread A: high priority, 90
• Thread B: low priority, 10
• Thread C: medium priority, 45

Furthermore, let's consider that we have some shared resource, X, which is coveted by threads A and B; this, of course, constitutes a critical ...