gaspersic/freeCodeCamp
1
0
Fork 0
Code Issues Pull Requests Projects Releases Wiki Activity

fix(guide): Fix all frontmatter

Browse Source
This commit is contained in:
Bouncey
2018-10-19 13:53:51 +01:00
committed by Stuart Taylor
parent 569bd7c3a7
commit 6d511c558a
146 changed files with 926 additions and 1469 deletions
Download Patch File Download Diff File Expand all files Collapse all files

17
guide/english/computer-science/deadlock/index.md
View File

@ -1,4 +1,9 @@
# Deadlocks
---
title: Deadlock
---
## Deadlock
### The Deadlock Problem
- A set of blocked processes each holding a resource and waiting to acquire a resource held by another process in the set.
- Example
@ -16,7 +21,7 @@
### Deadlock Characterization
Deadlock can arise if four conditions hold simultaneously.
- **Mutual exclusion** : only one process at a time can use a resource.
- **Mutual exclusion** : only one process at a time can use a resource.
- **Hold and wait** : a process holding at least one resource is waiting to acquire additional resources held by other processes.
- **No preemption** : a resource can be released only voluntarily by the process holding it, after that process has completed its task.
- **Circular wait** : there exists a set { P<sub>0</sub>, P<sub>1</sub>, …, P<sub>0</sub> } of waiting processes such that P<sub>0</sub> is waiting for a resource that is held by P<sub>1</sub>, P<sub>1</sub> is waiting for a resource that is held by P<sub>2</sub>, …, P<sub>n –1</sub> is waiting for a resource that is held by P<sub>n</sub>, and P<sub>0</sub> is waiting for a resource that is held by P<sub>0</sub>.
@ -28,16 +33,16 @@ Deadlock can arise if four conditions hold simultaneously.
### Deadlock Prevention
- **Mutual Exclusion** – It is not required for sharable resources; must hold for nonsharable resources.
- **Hold and Wait** – It must guarantee that whenever a process requests a resource, it does not hold any other resources.
- Require process to request and be allocated all its resources before it begins execution, or allow process to request resources only when the process has none.
- Low resource utilization; starvation possible.
- **No Preemption** –
- If a process that is holding some resources requests another resource that cannot be immediately allocated to it, then all resources currently being held are released.
- **No Preemption** –
- If a process that is holding some resources requests another resource that cannot be immediately allocated to it, then all resources currently being held are released.
- Preempted resources are added to the list of resources for which the process is waiting.
- Process will be restarted only when it can regain its old resources, as well as the new ones that it is requesting.
- **Circular Wait** – It imposes a total ordering of all resource types, and require that each process requests resources in an increasing order of enumeration.