The document discusses deadlocks in computer systems. It defines deadlock, presents examples, and describes four conditions required for deadlock to occur. Several methods for handling deadlocks are discussed, including prevention, avoidance, detection, and recovery. Prevention methods aim to ensure deadlocks never occur, while avoidance allows the system to dynamically prevent unsafe states. Detection identifies when the system is in a deadlocked state.
Deadlocks-An Unconditional Waiting Situation in Operating System. We must make sure of This concept well before understanding deep in to Operating System. This PPT will understands you to get how the deadlocks Occur and how can we Detect, avoid and Prevent the deadlocks in Operating Systems.
A brief introduction to Process synchronization in Operating Systems with classical examples and solutions using semaphores. A good starting tutorial for beginners.
Deadlocks-An Unconditional Waiting Situation in Operating System. We must make sure of This concept well before understanding deep in to Operating System. This PPT will understands you to get how the deadlocks Occur and how can we Detect, avoid and Prevent the deadlocks in Operating Systems.
A brief introduction to Process synchronization in Operating Systems with classical examples and solutions using semaphores. A good starting tutorial for beginners.
The Deadlock Problem
System Model
Deadlock Characterization
Methods for Handling Deadlocks
Deadlock Prevention
Deadlock Avoidance
Deadlock Detection
Recovery from Deadlock
This is the twelfth set of slightly updated slides from a Perl programming course that I held some years ago.
I want to share it with everyone looking for intransitive Perl-knowledge.
A table of content for all presentations can be found at i-can.eu.
The source code for the examples and the presentations in ODP format are on https://github.com/kberov/PerlProgrammingCourse
Gives an overview about Process, PCB, Process States, Process Operations, Scheduling, Schedulers, Interprocess communication, shared memory and message passing systems
Virtual Memory
• Copy-on-Write
• Page Replacement
• Allocation of Frames
• Thrashing
• Operating-System Examples
Background
Page Table When Some PagesAre Not in Main Memory
Steps in Handling a Page Fault
In the given presentation, process overview,process management scheduling typesand some more basic concepts were explained.
Kindly refere the presentation.
This Presentation is for Memory Management in Operating System (OS). This Presentation describes the basic need for the Memory Management in our OS and its various Techniques like Swapping, Fragmentation, Paging and Segmentation.
Deadlock is a very important topic in operating system. In this presentation slide, try to relate deadlock with real life scenario and find out some solution with two main algorithm- Safety and Banker's Algorithm.
The Deadlock Problem
System Model
Deadlock Characterization
Methods for Handling Deadlocks
Deadlock Prevention
Deadlock Avoidance
Deadlock Detection
Recovery from Deadlock
This is the twelfth set of slightly updated slides from a Perl programming course that I held some years ago.
I want to share it with everyone looking for intransitive Perl-knowledge.
A table of content for all presentations can be found at i-can.eu.
The source code for the examples and the presentations in ODP format are on https://github.com/kberov/PerlProgrammingCourse
Gives an overview about Process, PCB, Process States, Process Operations, Scheduling, Schedulers, Interprocess communication, shared memory and message passing systems
Virtual Memory
• Copy-on-Write
• Page Replacement
• Allocation of Frames
• Thrashing
• Operating-System Examples
Background
Page Table When Some PagesAre Not in Main Memory
Steps in Handling a Page Fault
In the given presentation, process overview,process management scheduling typesand some more basic concepts were explained.
Kindly refere the presentation.
This Presentation is for Memory Management in Operating System (OS). This Presentation describes the basic need for the Memory Management in our OS and its various Techniques like Swapping, Fragmentation, Paging and Segmentation.
Deadlock is a very important topic in operating system. In this presentation slide, try to relate deadlock with real life scenario and find out some solution with two main algorithm- Safety and Banker's Algorithm.
AVL Tree in Data Structures- It is height balanced tree with balance factor 1, -1 or 0. The different type of rotations used in this tree are: RR, LL, RL, LR
Overview of the fundamental roles in Hydropower generation and the components involved in wider Electrical Engineering.
This paper presents the design and construction of hydroelectric dams from the hydrologist’s survey of the valley before construction, all aspects and involved disciplines, fluid dynamics, structural engineering, generation and mains frequency regulation to the very transmission of power through the network in the United Kingdom.
Author: Robbie Edward Sayers
Collaborators and co editors: Charlie Sims and Connor Healey.
(C) 2024 Robbie E. Sayers
Water scarcity is the lack of fresh water resources to meet the standard water demand. There are two type of water scarcity. One is physical. The other is economic water scarcity.
CFD Simulation of By-pass Flow in a HRSG module by R&R Consult.pptxR&R Consult
CFD analysis is incredibly effective at solving mysteries and improving the performance of complex systems!
Here's a great example: At a large natural gas-fired power plant, where they use waste heat to generate steam and energy, they were puzzled that their boiler wasn't producing as much steam as expected.
R&R and Tetra Engineering Group Inc. were asked to solve the issue with reduced steam production.
An inspection had shown that a significant amount of hot flue gas was bypassing the boiler tubes, where the heat was supposed to be transferred.
R&R Consult conducted a CFD analysis, which revealed that 6.3% of the flue gas was bypassing the boiler tubes without transferring heat. The analysis also showed that the flue gas was instead being directed along the sides of the boiler and between the modules that were supposed to capture the heat. This was the cause of the reduced performance.
Based on our results, Tetra Engineering installed covering plates to reduce the bypass flow. This improved the boiler's performance and increased electricity production.
It is always satisfying when we can help solve complex challenges like this. Do your systems also need a check-up or optimization? Give us a call!
Work done in cooperation with James Malloy and David Moelling from Tetra Engineering.
More examples of our work https://www.r-r-consult.dk/en/cases-en/
Courier management system project report.pdfKamal Acharya
It is now-a-days very important for the people to send or receive articles like imported furniture, electronic items, gifts, business goods and the like. People depend vastly on different transport systems which mostly use the manual way of receiving and delivering the articles. There is no way to track the articles till they are received and there is no way to let the customer know what happened in transit, once he booked some articles. In such a situation, we need a system which completely computerizes the cargo activities including time to time tracking of the articles sent. This need is fulfilled by Courier Management System software which is online software for the cargo management people that enables them to receive the goods from a source and send them to a required destination and track their status from time to time.
Explore the innovative world of trenchless pipe repair with our comprehensive guide, "The Benefits and Techniques of Trenchless Pipe Repair." This document delves into the modern methods of repairing underground pipes without the need for extensive excavation, highlighting the numerous advantages and the latest techniques used in the industry.
Learn about the cost savings, reduced environmental impact, and minimal disruption associated with trenchless technology. Discover detailed explanations of popular techniques such as pipe bursting, cured-in-place pipe (CIPP) lining, and directional drilling. Understand how these methods can be applied to various types of infrastructure, from residential plumbing to large-scale municipal systems.
Ideal for homeowners, contractors, engineers, and anyone interested in modern plumbing solutions, this guide provides valuable insights into why trenchless pipe repair is becoming the preferred choice for pipe rehabilitation. Stay informed about the latest advancements and best practices in the field.
NO1 Uk best vashikaran specialist in delhi vashikaran baba near me online vas...Amil Baba Dawood bangali
Contact with Dawood Bhai Just call on +92322-6382012 and we'll help you. We'll solve all your problems within 12 to 24 hours and with 101% guarantee and with astrology systematic. If you want to take any personal or professional advice then also you can call us on +92322-6382012 , ONLINE LOVE PROBLEM & Other all types of Daily Life Problem's.Then CALL or WHATSAPP us on +92322-6382012 and Get all these problems solutions here by Amil Baba DAWOOD BANGALI
#vashikaranspecialist #astrologer #palmistry #amliyaat #taweez #manpasandshadi #horoscope #spiritual #lovelife #lovespell #marriagespell#aamilbabainpakistan #amilbabainkarachi #powerfullblackmagicspell #kalajadumantarspecialist #realamilbaba #AmilbabainPakistan #astrologerincanada #astrologerindubai #lovespellsmaster #kalajaduspecialist #lovespellsthatwork #aamilbabainlahore#blackmagicformarriage #aamilbaba #kalajadu #kalailam #taweez #wazifaexpert #jadumantar #vashikaranspecialist #astrologer #palmistry #amliyaat #taweez #manpasandshadi #horoscope #spiritual #lovelife #lovespell #marriagespell#aamilbabainpakistan #amilbabainkarachi #powerfullblackmagicspell #kalajadumantarspecialist #realamilbaba #AmilbabainPakistan #astrologerincanada #astrologerindubai #lovespellsmaster #kalajaduspecialist #lovespellsthatwork #aamilbabainlahore #blackmagicforlove #blackmagicformarriage #aamilbaba #kalajadu #kalailam #taweez #wazifaexpert #jadumantar #vashikaranspecialist #astrologer #palmistry #amliyaat #taweez #manpasandshadi #horoscope #spiritual #lovelife #lovespell #marriagespell#aamilbabainpakistan #amilbabainkarachi #powerfullblackmagicspell #kalajadumantarspecialist #realamilbaba #AmilbabainPakistan #astrologerincanada #astrologerindubai #lovespellsmaster #kalajaduspecialist #lovespellsthatwork #aamilbabainlahore #Amilbabainuk #amilbabainspain #amilbabaindubai #Amilbabainnorway #amilbabainkrachi #amilbabainlahore #amilbabaingujranwalan #amilbabainislamabad
Democratizing Fuzzing at Scale by Abhishek Aryaabh.arya
Presented at NUS: Fuzzing and Software Security Summer School 2024
This keynote talks about the democratization of fuzzing at scale, highlighting the collaboration between open source communities, academia, and industry to advance the field of fuzzing. It delves into the history of fuzzing, the development of scalable fuzzing platforms, and the empowerment of community-driven research. The talk will further discuss recent advancements leveraging AI/ML and offer insights into the future evolution of the fuzzing landscape.
Industrial Training at Shahjalal Fertilizer Company Limited (SFCL)MdTanvirMahtab2
This presentation is about the working procedure of Shahjalal Fertilizer Company Limited (SFCL). A Govt. owned Company of Bangladesh Chemical Industries Corporation under Ministry of Industries.
Vaccine management system project report documentation..pdfKamal Acharya
The Division of Vaccine and Immunization is facing increasing difficulty monitoring vaccines and other commodities distribution once they have been distributed from the national stores. With the introduction of new vaccines, more challenges have been anticipated with this additions posing serious threat to the already over strained vaccine supply chain system in Kenya.
2. DEADLOCKS
Definition and example of deadlock
System Model
Deadlock Characterization
Methods for Handling Deadlocks
Deadlock Prevention
Deadlock Avoidance
Deadlock Detection
Recovery from Deadlock
2
3. CHAPTER OBJECTIVES
To develop a description of deadlocks,
which prevent sets of concurrent
processes from completing their tasks.
To present a number of different
methods for preventing or avoiding
deadlocks in a computer system.
3
4. DEFINITION OF DEADLOCK
A set of two or more processes are deadlocked if
they are blocked (i.e., in the waiting state) each
holding a resource and waiting to acquire a
resource held by another process in the set.
Or
A process is deadlocked if it is waiting for an
event which is never going to happen.
Deadlocks can occur via system calls, locking, etc.
4
5. EXAMPLE OF DEADLOCK
Semaphores A and B, each initialized to 1:
P_0 P_1
---------- ----------
A.wait(); B.wait();
B.wait(); A.wait();
A.signal(); B.signal();
B.signal(); A.signal();
5
7. SYSTEM MODEL
System consists of resources
Resource types R1, R2, . . ., Rm
CPU cycles, memory space, I/O devices
Each resource type Ri has Wi instances.
Each process utilizes a resource as follows:
request
use
Release
7
8. DEADLOCK CHARACTERIZATION
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 {P0, P1, …, Pn} of
waiting processes such that P0 is waiting for a resource
that is held by P1, P1 is waiting for a resource that is held
by P2, …, Pn–1 is waiting for a resource that is held by Pn,
and Pn is waiting for a resource that is held by P0.
Deadlock can arise if four conditions hold simultaneously.
8
9. RESOURCE-ALLOCATION GRAPH
V is partitioned into two types:
P = {P1, P2, …, Pn}, the set consisting of all the
processes in the system
R = {R1, R2, …, Rm}, the set consisting of all
resource types in the system
request edge – directed edge Pi → Rj
assignment edge – directed edge Rj → Pi
A set of vertices V and a set of edges E.
9
14. BASIC FACTS
If graph contains no cycles ⇒ no deadlock
If graph contains a cycle ⇒
if only one instance per resource type, then
deadlock
if several instances per resource type,
possibility of deadlock
14
15. QUESTION 1
Suppose there are three processes P1, P2 and P3.
P1 requires 2 resources, P2 requires 3 resources
P3 requires 4 resources. What are the minimum
no. of resources required so that system will
never enter in deadlock?
Solution:
Assign one less no. of resources than required to
each process.
i.e. firstly assign 1---P1, 2---P2, 3---P3. Then, to
complete any of given process we simply need 1
more resource.
So total no resources required: 1+2+3+1=7
15
16. QUESTION 2
Suppose there are three processes P1, P2 and P3.
P1 requires 3 resources, P2 requires 5 resources
P3 requires 7 resources. What are the minimum
no. of resources required so that system will
never enter in deadlock?
Answer: 13
The minimum 13 resources are required so that
system must be in safe state.
16
17. MINIMUM RESOURCES REQUIRED
In general, minimum no. of resources required so
that system must be in safe state:
{(R1-1)+(R2-1)+(R3-1)+--------------+(Rn-1)}+1
(∑Ri-n)+1 where i is from 1 to n
17
(∑Ri-n)+1
18. QUESTION 3
Suppose there are five processes P1, P2, P3, P4
and P5. P1 requires 4 resources, P2 requires 3
resources, P3 requires 2 resources, P4 requires 9
resources, P5 requires 8 resources. What are the
minimum no. of resources required so that
system will never enter in deadlock?
Solution:
R=26, n=5.
Minimum no. of resources required: 26-5+1=22
18
19. MAXIMUM PROCESSES FOR SAFE
STATE
If total no. of resources and need of each
process are given, then no. of process can also
be calculated.
This can be calculated by using same concept.
19
20. QUESTION 4
Suppose each process needs 5 units of resources
and total no. of resources are 15. What are the
maximum no. of process should run in safe state?
Solution:
(r-1)*n +1<=R where r is no. of resources
required, n is no. of processes, R is total no. of
process.
r=5, R=15
(5-1)*n+1<=15 => 4*n+1<=15
n<=14/4 => n<=3.5
So, no. of max. processes n=3 20
21. QUESTION 5
Suppose each process needs 3 units of resources
and total no. of resources are 100. What are the
maximum no. of process should run in safe state?
Answer :49
21
22. METHODS FOR HANDLING
DEADLOCKS
Ensure that the system will never enter a
deadlock state:
Deadlock prevention
Deadlock avoidence
Allow the system to enter a deadlock state and
then recover
Ignore the problem and pretend that deadlocks
never occur in the system; used by most
operating systems, including UNIX
22
23. DEADLOCK PREVENTION
Mutual Exclusion – not required for
sharable resources (e.g., read-only files); must
hold for non-sharable resources
Hold and Wait – 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 allocated to it.
Low resource utilization; starvation
possible
Restrain the ways request can be made
23
24. DEADLOCK PREVENTION (CONT.)
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 – impose a total ordering of all
resource types, and require that each process
requests resources in an increasing order of
enumeration
24
25. DEADLOCK AVOIDANCE
Simplest and most useful model requires
that each process declare the maximum
number of resources of each type that it
may need
The deadlock-avoidance algorithm
dynamically examines the resource-
allocation state to ensure that there can
never be a circular-wait condition
Resource-allocation state is defined by the
number of available and allocated resources,
and the maximum demands of the processes
Requires that the system has some additional a priori information
available
25
26. SAFE STATE
When a process requests an available resource, system
must decide if immediate allocation leaves the system in a
safe state
System is in safe state if there exists a sequence <P1, P2,
…, Pn> of ALL the processes in the systems such that for
each Pi, the resources that Pi can still request can be
satisfied by currently available resources + resources held
by all the Pj, with j < I
That is:
If Pi resource needs are not immediately available,
then Pi can wait until all Pj have finished
When Pj is finished, Pi can obtain needed resources,
execute, return allocated resources, and terminate
When Pi terminates, Pi +1 can obtain its needed
resources, and so on
26
27. BASIC FACTS
If a system is in safe state ⇒ no deadlocks
If a system is in unsafe state ⇒ possibility
of deadlock
Avoidance ⇒ ensure that a system will
never enter an unsafe state.
27
29. AVOIDANCE ALGORITHMS
Single instance of a resource type
Use a resource-allocation graph
Multiple instances of a resource type
Use the banker’s algorithm
29
30. RESOURCE-ALLOCATION GRAPH
SCHEME
Claim edge Pi → Rj indicated that process Pj
may request resource Rj; represented by a
dashed line
Claim edge converts to request edge when a
process requests a resource
Request edge converted to an assignment edge
when the resource is allocated to the process
When a resource is released by a process,
assignment edge reconverts to a claim edge
Resources must be claimed a priori in the
system
30
33. RESOURCE-ALLOCATION GRAPH
ALGORITHM
Suppose that process Pi requests a resource Rj
The request can be granted only if converting
the request edge to an assignment edge does
not result in the formation of a cycle in the
resource allocation graph
33
34. BANKER’S ALGORITHM
Multiple instances
Each process must a priori claim maximum
use
When a process requests a resource it may
have to wait
When a process gets all its resources it must
return them in a finite amount of time
34
35. DATA STRUCTURES FOR THE BANKER’S
ALGORITHM
Available: Vector of length m. If available [j] = k, there are k
instances of resource type Rj available
Max: n x m matrix. If Max [i,j] = k, then process Pi may
request at most k instances of resource type Rj
Allocation: n x m matrix. If Allocation[i,j] = k then Pi is
currently allocated k instances of Rj
Need: n x m matrix. If Need[i,j] = k, then Pi may need k more
instances of Rj to complete its task
Need [i,j] = Max[i,j] – Allocation [i,j]
Let n = number of processes, and m = number of resources types.
35
36. SAFETY ALGORITHM
1. Let Work and Finish be vectors of length m and n, respectively.
Initialize:
Work = Available
Finish [i] = false for i = 0, 1, …, n- 1
2. Find an i such that both:
(a) Finish [i] = false
(b) Needi ≤ Work
If no such i exists, go to step 4
3. Work = Work + Allocationi
Finish[i] = true
go to step 2
4. If Finish [i] == true for all i, then the system is in a safe state
36
37. RESOURCE-REQUEST ALGORITHM FOR
PROCESS PI
Requesti = request vector for process Pi. If Requesti [j] = k
then process Pi wants k instances of resource type Rj
1. If Requesti ≤ Needi go to step 2. Otherwise, raise error
condition, since process has exceeded its maximum claim
2. If Requesti ≤ Available, go to step 3. Otherwise Pi must
wait, since resources are not available
3. Pretend to allocate requested resources to Pi by modifying
the state as follows:
Available = Available – Requesti;
Allocationi = Allocationi + Requesti;
Needi = Needi – Requesti;
If safe ⇒ the resources are allocated to Pi
If unsafe ⇒ Pi must wait, and the old resource-allocation
state is restored
37
38. EXAMPLE OF BANKER’S ALGORITHM
5 processes P0 through P4;
3 resource types:
A (10 instances), B (5instances), and C (7 instances)
Snapshot at time T0:
Allocation Max Available
A B C A B C A B C
P0 0 1 0 7 5 3 3 3 2
P1 2 0 0 3 2 2
P2 3 0 2 9 0 2
P3 2 1 1 2 2 2
P4 0 0 2 4 3 3
38
39. EXAMPLE (CONT.)
The content of the matrix Need is defined to be Max – Allocation
Need
A B C
P0 7 4 3
P1 1 2 2
P2 6 0 0
P3 0 1 1
P4 4 3 1
The system is in a safe state since the sequence < P1, P3, P4, P2, P0>
satisfies safety criteria
39
40. EXAMPLE: P1 REQUEST (1,0,2)
Check that Request ≤ Available (that is, (1,0,2) ≤ (3,3,2) ⇒ true
Allocation Need Available
A B C A B C A B C
P0 0 1 0 7 4 3 2 3 0
P1 3 0 2 0 2 0
P2 3 0 2 6 0 0
P3 2 1 1 0 1 1
P4 0 0 2 4 3 1
Executing safety algorithm shows that sequence < P1, P3, P4, P0, P2>
satisfies safety requirement
Can request for (3,3,0) by P4 be granted?
Can request for (0,2,0) by P0 be granted? 40
42. SINGLE INSTANCE OF EACH RESOURCE
TYPE
Maintain wait-for graph
Nodes are processes
Pi → Pj if Pi is waiting for Pj
Periodically invoke an algorithm that searches for
a cycle in the graph. If there is a cycle, there
exists a deadlock
An algorithm to detect a cycle in a graph requires
an order of n2
operations, where n is the number
of vertices in the graph
42
44. SEVERAL INSTANCES OF A
RESOURCE TYPE
Available: A vector of length m indicates
the number of available resources of each
type
Allocation: An n x m matrix defines the
number of resources of each type currently
allocated to each process
Request: An n x m matrix indicates the
current request of each process. If Request
[i][j] = k, then process Pi is requesting k
more instances of resource type Rj. 44
45. DETECTION ALGORITHM
1.Let Work and Finish be vectors of length m and
n, respectively Initialize:
(a) Work = Available
(b)For i = 1,2, …, n, if Allocationi ≠ 0, then
Finish[i] = false; otherwise, Finish[i] = true
2.Find an index i such that both:
(a)Finish[i] == false
(b)Requesti ≤ Work
If no such i exists, go to step 4
45
46. DETECTION ALGORITHM (CONT.)
3.Work = Work + Allocationi
Finish[i] = true
go to step 2
4.If Finish[i] == false, for some i, 1 ≤ i ≤ n, then
the system is in deadlock state. Moreover, if
Finish[i] == false, then Pi is deadlocked
Algorithm requires an order of O(m x n2
)
operations to detect whether the system is in
deadlocked state
46
47. EXAMPLE OF DETECTION
ALGORITHM
Five processes P0 through P4;three resource types
A (7 instances), B (2 instances), and C (6 instances)
Snapshot at time T0:
Allocation Request Available
A B C A B C A B C
P0 0 1 0 0 0 0 0 0 0
P1 2 0 0 2 0 2
P2 3 0 3 0 0 0
P3 2 1 1 1 0 0
P4 0 0 2 0 0 2
Sequence <P0, P2, P3, P1, P4> will result in Finish[i] = true for all i
47
48. EXAMPLE (CONT.)
P2 requests an additional instance of type C
Request
A B C
P0 0 0 0
P1 2 0 2
P2 0 0 1
P3 1 0 0
P4 0 0 2
State of system?
Can reclaim resources held by process P0, but insufficient
resources to fulfill other processes; requests
Deadlock exists, consisting of processes P1, P2, P3, and P4
48
49. DETECTION-ALGORITHM USAGE
When, and how often, to invoke depends on:
How often a deadlock is likely to occur?
How many processes will need to be rolled
back?
one for each disjoint cycle
If detection algorithm is invoked arbitrarily,
there may be many cycles in the resource graph
and so we would not be able to tell which of the
many deadlocked processes “caused” the
deadlock.
49
50. RECOVERY FROM DEADLOCK: PROCESS
TERMINATION
Abort all deadlocked processes
Abort one process at a time until the deadlock cycle is eliminated
In which order should we choose to abort?
1. Priority of the process
2. How long process has computed, and how much longer to
completion
3. Resources the process has used
4. Resources process needs to complete
5. How many processes will need to be terminated
6. Is process interactive or batch?
50
51. RECOVERY FROM DEADLOCK: RESOURCE
PREEMPTION
Selecting a victim – minimize cost
Rollback – return to some safe state, restart
process for that state
Starvation – same process may always be picked
as victim, include number of rollback in cost factor
51