Threads And Concurrency Questions Long
A deadlock in multithreading refers to a situation where two or more threads are unable to proceed because each thread is waiting for a resource that is held by another thread in the same group. In other words, it is a state where two or more threads are stuck in a circular dependency, causing a halt in the execution of the program.
Deadlocks occur due to the following four necessary conditions:
1. Mutual Exclusion: At least one resource must be held in a non-sharable mode, meaning only one thread can access it at a time.
2. Hold and Wait: A thread holding a resource is waiting to acquire another resource that is currently being held by another thread.
3. No Preemption: Resources cannot be forcibly taken away from a thread; they can only be released voluntarily.
4. Circular Wait: A circular chain of two or more threads exists, where each thread is waiting for a resource held by another thread in the chain.
When these conditions are met, a deadlock can occur. Once a deadlock happens, the threads involved will remain in a blocked state indefinitely, resulting in a program freeze or crash.
To prevent deadlocks, various techniques can be employed, such as:
1. Resource Ordering: Ensuring that threads always request resources in the same order, preventing circular wait conditions.
2. Resource Allocation Graph: Analyzing the resource allocation graph to detect potential deadlocks and taking appropriate actions to avoid them.
3. Deadlock Detection and Recovery: Implementing algorithms to detect deadlocks and recover from them by releasing resources or terminating threads.
4. Avoidance: Using algorithms that dynamically analyze resource requests and predict if they will lead to a deadlock. If a potential deadlock is detected, the request can be delayed or denied.
It is crucial to design multithreaded programs carefully, considering the potential for deadlocks and implementing appropriate strategies to prevent or handle them.