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Deadlock problem and solution

Deadlock problem and solution. Speaker: Mrak Date: 2012-12-12. Outline. Introduction Deadlock Prevention Deadlock Avoidance Deadlock Detection & Recovery Conclusion Reference. Deadlock introduction. Deadlock DEF: 系統中有 processes 呈現一種互相等待對方資源釋放出來的情況 (circular waiting) 使的這些 process 皆

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Deadlock problem and solution

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  1. Deadlock problem and solution Speaker: Mrak Date: 2012-12-12

  2. Outline • Introduction • Deadlock Prevention • Deadlock Avoidance • Deadlock Detection & Recovery • Conclusion • Reference

  3. Deadlock introduction • Deadlock DEF: • 系統中有processes呈現一種互相等待對方資源釋放出來的情況(circular waiting) • 使的這些process皆 無法往下執行，使 的CPU utilization降 低。 Fig . 1

  4. Deadlock introduction • Mutual exclusion • Fig. 1.1 • Hold&wait • No preemption • Circular waiting • Fig. 2

  5. Deadlock prevention • Howtoprevention-破除下列四點 • Mutual exclusion • Hold&wait • No preemption • priority • Circular waiting • Unique resource ID • Ascending

  6. Deadlock prevention • Circular waiting • Example:

  7. Deadlock prevention • Circular waiting • PF :ascending (Fig. 3) • p1 < p2 <……< pn < p1 • => p1 < p1 --><--

  8. Deadlock avoidance • DEF • 當某process提出資源申請後，OS必須持行一個algorithm(Banker’s)以判斷定process提出的申請後，系統是否除與安全的狀況(不會進入死結)

  9. Deadlock avoidance-banker’s • Example P1提出Request = (1,0,2) 是否核准 Setp1:check Request(P1)<= Need(P1) Setp2:check Request(P1)<=Available Setp3:Allocation+=Request Need-=Request Available-=Request Setp4:run safety algorithm (1,0,2) <= (1,2,2) (1,0,2) <= (3,3,2) (2,0,0) + (1,0,2) =(3,0,2) (1,2,2) - (1,0,2) =(0,2,0) (3,3,2) - (1,0,2) =(2,3,0)

  10. Deadlock avoidance-Safety algorithm Step1:work=available; Finish = Step2:可找到P1滿足 (i)Finish[1]=false (ii)Need1 < work go step3 (0,2,0) < (2,3,0) Step3:Finish[1]=True 且work+=Allocation1 if Finish中還有false goto step 3 else goto step4 Step4:check Finish 皆為True 傳回safe state Sate sequence = p1 , p3 , p4 , p0 , p2

  11. Deadlock Detection & Recovery • Detection DEF: • 每X秒偵測deadlock是否存在，若存在必須恢復正常 Step1: work=Available Finish[i] = if Allocation ≠ 0 set false (0,0,0) if Allocation = 0 set true Step2: 如果找到Pi滿足 (i) Finish[i] = False (ii) Requesti <=work then goto step 3 else goto step 4 Step3:set Finish[i] = true work += Allocationi then goto step 2 Step4: check Finish Array if all is true , No Deadlock

  12. Deadlock Detection & Recovery • Recovery DEF: • Case 1 : kill all process in Deadlock • Case 2 : kill one process each time,then Detection

  13. Conclusion • Deadlock Prevention與Deadlock Avoidance的resources utilization 保證系統不會有deadlock • Deadlock Detection & Recovery resources utilization 但系統可能進入deadlock

  14. reference • https://docs.google.com/a/mail1.ncnu.edu.tw/viewer?a=v&q=cache:t-E9tdn2zpIJ:sjchen.im.nuu.edu.tw/OS/97Spring/Ch_6.pdf+&hl=zh-TW&pid=bl&srcid=ADGEESixtvIiw8J9u-2S89vjdn-umwFUUphLv6k6Z7vT3dflJV1GxvKKTBpqF6C7V4S-C1qV_Hb5WDNVAaArSi9z4Ne4pmoESx5siFAv_edb7WFDgXGX-s4njkpON-u1zcQDqIFWy-jn&sig=AHIEtbTNMCCDDCa0kjMpauyT9mndv7ZxWA[聯合大學] • http://kramli.staff.ui.ac.id/files/2011/02/Chapter-06-OS-Concurrency-Deadlock-and-Starvation.pdf[Manatee Community College]

  15. Q&A

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