Two conditions must hold for a deadlock to occur with reusable resources:

  1. Hold and wait: A process is already holding one resource and is requesting another resource.
  2. Circular wait: A process must issue a resource request that closes a cycle involving at least two processes and two resources.

Deadlock is structurally impossible if either of the two conditions are eliminated.

Eliminating Hold and Wait

Several alternatives to eliminating the hold-and-wait condition exist:

  1. Every process must request all resources ever needed at the same time. While simple, this leads to poor resource utilization since resources are held for unnecessarily long periods of time and thus unavailable to other processes.
  2. Every process must release all currently held resources prior to making any new request. Improves utilization but results in repeated requests and releases of frequently used resources.
  3. A process can be given the ability to test whether a needed resource is currently available. The process must release all currently held resources only if the requested resource is not currently available. Otherwise the new resource may be requested and allocated immediately.

Static Deadlock Prevention was originally found on Access 2 Learn

Assistant Professor

Walter Wimberly is an Assistant Professor at a regional college in Tennessee, teaching Computer Science in the Software Engineering track. He works as a student advisor, oversees curriculum changes, develops new courses, and manages the advisory panel.
Walter taught full time for about 7 years, before going back into “industry” as a full stack Software Developer for a dozen years. There he focused on web based projects coding in JavaScript/jQuery and utilizing the Bootstrap CSS Framework on the front-end, and coding in PHP, ASP/ASP.Net, SQL on the back-end.

Since he loves teaching, he taught as an adjunct web and digital media classes for eight (8) years, while working in industry, and has since returned to teaching full time.

He has been married for over 25 years, and is father to several special needs boys. As such, he is working on some projects to help others who have special needs to be self-sufficient, and support the care givers of those with special needs. Check out his Autism blog for more info.

Similar Posts

Semaphores

ByWalter Wimberly

The software solution presented before only works if there is two processes competing for the same code block. Likewise, it is not real efficient if it needs to be used a lot. Semaphores are general-purpose primitives that allow solving a variety of synchronization problems in a systematic manner. A semaphore is a non-negative integer variable that…

Deadlock Detection

ByWalter Wimberly

A deadlock in a resource allocation graph can be detected by executing a graph reduction algorithm by repeating this process: Select an unblocked process p. Remove p, including all request and allocation edges connected to p. Anything left is blocked, and risks deadlock. However, it is considered completely reducible if there are no processes left…

The Implementation of Semaphores

ByWalter Wimberly

Most contemporary computer architectures offer hardware support for process synchronization in the form of specialized machine instructions. The test-and-set instruction (TS) copies a variable into a register and sets the variable to zero in one indivisible machine cycle. Test-and-set has the form TS(R, x) where R is a register and x is a memory location and performs…

Classic Synchronization Problems

ByWalter Wimberly

The Readers-Writers Problem The readers-writers problem is an extension of the critical section problem where two types of processes, readers and writers. However, it involves an interesting issue when the processes compete for access to a common resource. Multiple readers are allowed to enter the critical section concurrently but only one writer is allowed to…