Concurrent Systems II - Bad Request - Trinity College Dublin

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Semaphores • Semaphore = sema [signal] + phoros [bearer] (from Greek). • Historically, semaphores were used for long-distance optical signalling, e.g. lanterns, flags, coloured arms, etc. ◾ E.g. Semaphores (“the Chappe system”) were used in France from late 1700s to mid 1800s for military and governmental use. 66 Trinity College Dublin © Mike Brady 2007
Semaphores • Computer Semaphores [specifically “counting semaphores”] invented by Edsger W. Dijkstra, named after signalling semaphores. • Can be thought of as a special case of a condition variable, a nonnegative counter value. • Producer and Consumer Threads • Can be implemented as a special case of Condition Variables 67 Trinity College Dublin © Mike Brady 2007
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Concurrent Systems II (CS3D4/CS3BA2
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POSIX Threads • POSIX Threads aka
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Six Separate Threads Master Thread
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Where… • ‘thread’ is the ID
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Hello World -- Creating Threads int
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Hello World -- Thread Function void
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Wilde/Stoker/Ubuntu h-3.1$ cc -lpth
Page 15 and 16: Interaction • No thread interacti
Page 17 and 18: Interactions & Dependencies • Int
Page 19 and 20: …to do Parallel Programming • H
Page 21 and 22: Hardware Main Memory Level 2 Cache
Page 23 and 24: Shared Memory Machine • Each proc
Page 25 and 26: Concurrent Program • A Concurrent
Page 27 and 28: Communication • A parallel progra
Page 29 and 30: 1 - Flow Dependence S1: write to lo
Page 31 and 32: 3 - Output Dependence S1: write to
Page 33 and 34: Dependence in Loops j k k i 1 2 j 5
Page 35 and 36: How can we transform it? • We can
Page 37 and 38: Issues: • The variable sum, as wr
Page 39 and 40: Summarising: • We could paralleli
Page 41 and 42: Example • Sample function: y = 0.
Page 43 and 44: Synchronisation • We’ve looked
Page 45 and 46: Shared Variable S: Thread 1 after T
Page 47 and 48: Mutual Exclusion in pthreads. • M
Page 49 and 50: Shared Variable S Protected by Mute
Page 51 and 52: Lock and Unlock Mutex • pthread_m
Page 53 and 54: } /********** Critical Section ****
Page 55 and 56: Problem Tutorial • The transpose
Page 57 and 58: Producers and Consumers • Essenti
Page 59 and 60: Condition Variables (2) • Dramati
Page 61 and 62: From Thread U’s POV (2) • If C
Page 63 and 64: From Thread U’s POV (4) • Acqui
Page 65: Thread S (2) • Acquire Mutex M
Page 69 and 70: Semaphore Consumer ◾Acquire Mutex
Page 71 and 72: Semaphores (3) • Useful for count
Page 73 and 74: Sample Solution for ∏ • Calcula
Page 75 and 76: unsigned long long clock_cycles() {
Page 77 and 78: The Challenge of Concurrency • Co
Page 79 and 80: Concurrent Execution • A concurre
Page 81 and 82: Notation Trivial Concurrent Program
Page 83 and 84: Trivial Concurrent Program p1: n
Page 85 and 86: Example — Jumping Frogs • A fro
Page 87 and 88: If the frogs can only move “forwa
Page 89 and 90: State Diagrams for Processes • A
Page 91 and 92: Book Reference Principles of concur
Page 93 and 94: Correctness • (Correctness in Seq
Page 95 and 96: Using State machines • We can des
Page 97 and 98: The Critical Section Problem (2)
Page 99 and 100: Observations & Implications • Rem
Page 101 and 102: Simplify Critical Section Problem i
Page 103 and 104: State Transitions r1,s1,1 r1: await
Page 105 and 106: Deadlock Free? • Deadlock Free: I
Page 107 and 108: Scorecard Mutual Exclusion Deadlock
Page 109 and 110: Attempt #2 Critical Section Problem
Page 111 and 112: Attempt #2 Fails… • Attempt 2 f
Page 113 and 114: Attempt #3 Critical Section Problem
Page 115 and 116: Attempt #3 Fails… • Attempt 3 f
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Attempt #4 loop forever Critical Se
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Attempt #4 Fails… • Attempt 3 f
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Attempt #5, derived from #4 Critica
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Verification of concurrent programs
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A quick overview of some mathematic
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A quick overview of some mathematic
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Proving correctness by induction
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A quick overview of some temporal l
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A quick overview of some temporal l
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Temporal logic at work • Consider
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Promela • Promela [Protocol/Proce
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Process (2) • A process type (pro
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SPIN Hello World Example SPIN = Sim
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Promela Variables (2) • Arrays
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Statements (2) • The skip stateme
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If Statement if :: (n % 2 != 0) ->
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Atomic Statement atomic { stat1; st
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Process Execution / Evaluation Sema
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The Closed World Assumption • The
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Process memory management • In a
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Virtual memory • Give each proces
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Virtual memory 0 0 process 1 2 32 0
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Memory management requirements and
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E.g. Virtual memory implementation
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Multi-level page tables Virtual add
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Typical process memory layout memor
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Translation look aside buffer • E
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Page fault handling Start Access pa
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Fetch policy • When should a page
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Page replacement policy • A page
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Page replacement policy • First-I
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Clock Algorithm 179 Trinity College
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Resident set management • Variabl
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Resident set management Local Repla
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Resident set management Δ Working
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Resident set management 187 Trinity
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Cleaning policy • Page buffering
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Load control • We can use a few d
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Process state transitions • Proce
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Preemptive and nonpreemptive schedu
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Scheduling algorithms • First-Com
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Scheduling algorithms • Shortest-
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Scheduling algorithms • Priority
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Scheduling algorithms • Round-Rob
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Example Process Arrival Time Next B
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Scheduling algorithms • Multi-lev
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Scheduling algorithms • Multi-lev
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Multi-processor scheduling • Flyn
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Layered file I/O (1) Application Di
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Disk access • Disks are slow ◾
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Disk scheduling • So, the order i
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Disk scheduling algorithms (2) •
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Concurrent Systems II - Bad Request - Trinity College Dublin

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