What are the 4 types of deadlock?

Deadlocks in operating systems can be classified based on the type of resources and the situations causing them. Here are the four main types of deadlock:

1. Resource Deadlock

This occurs when processes compete for non-shareable resources and hold them while waiting for additional resources.

Example

• Process A holds Resource X and requests Resource Y.
• Process B holds Resource Y and requests Resource X.
• Both processes are stuck, waiting indefinitely.

Key Features

• Involves physical or logical resources (e.g., files, memory, printers).
• Results from circular wait and hold-and-wait conditions.

2. Communication Deadlock

This type arises when processes are waiting for messages or signals from each other to proceed, but none can send or receive due to cyclic dependencies.

Example

• Process A waits for a message from Process B.
• Process B waits for a message from Process A.
• Neither process progresses.

Key Features

• Involves inter-process communication (IPC) mechanisms.
• Common in distributed systems and message-passing scenarios.

3. Thread Deadlock

Occurs in multithreading environments when threads within a single process block each other by competing for shared resources.

Example

• Thread 1 locks Resource X and waits for Resource Y.
• Thread 2 locks Resource Y and waits for Resource X.

Key Features

• Involves synchronization issues with mutexes, semaphores, or locks.
• Common in applications using multithreading.

4. Circular Wait Deadlock

This is a generic form where a cycle of processes exists, and each process is waiting for a resource held by the next process in the cycle.

Example

• Process A → waits for Resource X held by Process B.
• Process B → waits for Resource Y held by Process C.
• Process C → waits for Resource Z held by Process A.

Key Features

• A direct result of the circular wait condition.
• Often resolved by breaking the circular dependency.

How to Prevent or Handle Deadlocks

• Avoidance Techniques: Use algorithms like the Banker's Algorithm to allocate resources safely.
• Prevention Strategies: Remove one of the four necessary conditions for deadlocks.
• Detection and Recovery: Periodically check for deadlocks and resolve them by terminating or rolling back processes.

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