4.5 Prevention and Handling Strategies

Overcoming Deadlock 
 Since detecting and recovering from a deadlock in an embedded system is very difficult, the best approach is prevention. This is done by breaking one of the four Coffman conditions. 
 
 Break Circular Wait : Enforce a strict lock ordering for all resources. If all tasks are required to lock Mutex 1 before Mutex 2, the deadlock scenario described above could never happen. This is the most common and effective deadlock prevention strategy 
 Break Hold and Wait : Request all required resources at once. 
 Detection and Recovery : Mechanisms like a wait-for graph can be used to detect cycles. If a deadlock is detected, the system can recover by aborting one of the tasks (termination) or forcibly taking a resource (preemption). However, this is rarely implemented on microcontrollers.
 
 
 
 
 Overcoming Priority Inversion and Starvation 
 
 
 Priority Inheritance : This is the solution to priority inversion. If a high-priority task is blocked waiting for a mutex held by a low-priority task, the low-priority task will temporarily "inherit" the priority of the high-priority task. This allows the low-priority task to run quickly, finish its work, and release the mutex as soon as possible. 
 Note: Mutexes in FreeRTOS already implement this mechanism automatically. 
 
 
 Priority Ceiling : Each resource is assigned a priority ceiling, which is the highest priority level of any task that can access it. When a task locks the resource, its priority is immediately raised to that ceiling level until it releases it. 
 
 
 Aging : To prevent starvation, the priority of a task that has been waiting for a long time can be gradually increased. This way, a low-priority task will eventually have a high enough priority to be executed. 
 
 
 Fair Scheduling : Using a scheduling algorithm (like round-robin for tasks of the same priority) to ensure all tasks get a fair share of CPU time.