The document discusses different methods for deadlock prevention including: 1) Ensuring that at least one of the four conditions for deadlock (mutually exclusive, hold and wait, no preemption, circular wait) does not occur. 2) Converting non-shareable resources to shareable resources to prevent mutual exclusion. 3) Having processes request all resources before starting or only request resources when none are held to prevent hold and wait. 4) Allowing preemption of resources from waiting processes to prevent no preemption. 5) Requiring processes request resources in a standardized order to prevent circular wait.

1. DEADLOCK PREVENTIONDEADLOCK PREVENTION
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2. DEADLOCK PREVENTIONDEADLOCK PREVENTION
• Deadlock prevention means that take theDeadlock prevention means that take the
preventive methods before the deadlockpreventive methods before the deadlock
occurs.occurs.
• To prevent the occurance of a deadlock, byTo prevent the occurance of a deadlock, by
ensuring that atleast one of these conditionsensuring that atleast one of these conditions
(i.e. mutually exclusive, no-preemption, hold(i.e. mutually exclusive, no-preemption, hold
and wait and circular wait) can not hold.and wait and circular wait) can not hold.
• System may cause side effects i.e. low deviceSystem may cause side effects i.e. low device
utilization and reduced system throughput.utilization and reduced system throughput.

3. MUTUAL EXCLUSIONMUTUAL EXCLUSION
• It means only one process can use theIt means only one process can use the
resource.resource.
• The resource are in non-shareable mode only.The resource are in non-shareable mode only.
• This condition is denied byThis condition is denied by
““Convert the all non-shareableConvert the all non-shareable
resources to shareable resources”resources to shareable resources”
• Applying the above method to prevent theApplying the above method to prevent the
deadlock.deadlock.

4. HOLD-WAITHOLD-WAIT
• A process may hold a resource of the same time itA process may hold a resource of the same time it
requests another one resource that are held by otherrequests another one resource that are held by other
processes.processes.
• This condition is denied byThis condition is denied by
1.1. A process request the resources only whenA process request the resources only when
the process has none.the process has none.
2.2. Each process to request resources and beEach process to request resources and be
allocated all its resources before it beginsallocated all its resources before it begins
execution.execution.
• Applying these methods to prevent the deadlock.Applying these methods to prevent the deadlock.

5. NO-PREEMPTIONNO-PREEMPTION
• IIt means resources are not released in thet means resources are not released in the
middle of the processing of a resource.middle of the processing of a resource.
• This condition is denoted byThis condition is denoted by
1.1. A process requests some resources, toA process requests some resources, to
check whether they are allocated tocheck whether they are allocated to
waiting process.waiting process.
2.2. If so, we preempt the desired resourcesIf so, we preempt the desired resources
from the waiting process and allocatefrom the waiting process and allocate
them to the requesting process.them to the requesting process.

6. CIRCULAR WAITCIRCULAR WAIT
• It means processes are waiting for resourcesIt means processes are waiting for resources
that are held by operation processes inthat are held by operation processes in
circular way.circular way.
• This condition is defined byThis condition is defined by
– It improve a total ordering of all resources.It improve a total ordering of all resources.
– It require that each process requestsIt require that each process requests
resources in an increasing order ofresources in an increasing order of
enumeration.enumeration.