deadlockfree

Deadlockfree is the property of a system, typically a concurrent or distributed system, in which deadlocks cannot occur. A deadlock is a situation where a set of processes waits indefinitely for resources held by each other, resulting in no progress. The concept is tied to the four Coffman conditions for deadlock: mutual exclusion, hold and wait, no preemption, and circular wait; eliminating or mitigating any of these conditions can render a system deadlockfree.

Achieving deadlock freedom involves design choices that prevent circular waiting or resource contention from causing indefinite blocking. Common approaches include:

- Resource ordering: requiring that all processes acquire resources in a globally fixed order, which prevents circular wait.

- All-at-once requests or preemption: processes request all needed resources at once or have resources preempted to break waits.

- Non-blocking synchronization: using lock-free or wait-free data structures to avoid blocking entirely.

- Try-lock with backoff: attempting to acquire a lock and backing off or retrying in a way that avoids cyclic dependencies.

- Resource brokers or hierarchies: using a centralized mechanism to grant resources, avoiding arbitrary interleavings.

In distributed systems and databases, deadlockfree design may be complemented by timeouts, deadlock detection with subsequent rollback, or scheduling policies that guarantee progress under contention. Verification methods such as formal proofs, model checking, or static analysis are often employed to establish deadlock freedom for critical components.

Applications span operating systems, database transaction managers, concurrent data structures, and real-time systems. While deadlockfreedom improves liveness, it can constrain concurrency or increase complexity, so trade-offs are typically considered during design.