Deadlock huwa stat fejn żewġ threads jew aktar huma kollha imblukkati għal dejjem, kull wieħed jistenna riżorsa li jżomm ieħor. Xejn ma jagħmel progress.
L-erba' kundizzjonijiet meħtieġa (Coffman)
L-erbgħa kollha jridu jseħħu f'daqqa — neħħi kwalunkwe waħda u d-deadlock huwa impossibbli:
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1. Mutual exclusion → a resource is held exclusively (only one holder at a time)
2. Hold and wait → a thread holds one resource while waiting to acquire another
3. No preemption → resources can't be forcibly taken; only released voluntarily
4. Circular wait → a cycle: T1 waits for R2 (held by T2), T2 waits for R1 (held by T1)