Chapter14_PPT

– In each case, thread eventually returns to Started state – Thread method Interrupt returns waiting or sleeping threads to Started state
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Chapter 14 - Multithreading
Outline
14.1 14.2 14.3 14.4 14.5 14.6 14.7 Introduction Thread States: Life Cycle of a Thread Thread Priorities and Thread Scheduling Thread Synchronization and Class Monitor Producer/Consumer Relationship without Thread Synchronization Producer/Consumer Relationship with Thread Synchronization Producer/Consumer Relationship: Circular Buffer
• Upcoming example: Threads sleeping and printing
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Priority Highest
A C
B
Priority AboveNormal
Priority Normal
Priority BelowNormal
number of Constructor milliseconds for thread to wait
5 seconds
' method Print controls thread that prints messages Public Sub Print() Name property ' obtain reference to Dim current As Thread
• Creating a thread
– Create instance of class Thread – Thread begins in Unstarted state
• Started state
– Indicates thread is ready to execute – Entered when method Start is called on an Unstarted thread
.2
Thread States: Life Cycle of a Thread
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• Thread states
– At any time, each thread is in one of several thread states – Indicates how thread should execute
• Blocked state
– Entered when thread issues an input/output request – When request is complete, thread returns to Started state
2002 Prentice Hall. All rights reserved.
All rights reserved.
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14.1 Introduction
• Multithreading
– Allows concurrent execution of multiple tasks:
• Compiling a program • Sending a file to a printer • Receiving email messages
Thread.Sleep(sleepTime)
' print thread name Console.WriteLine( & " done sleeping") End Sub ' Print End Class ' CMessagePrinter
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• ThreadStart delegate terminates • Program calls Thread object’s Abort method – Throws a ThreadAbortException in the thread
– Normally causes thread to terminate
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• Suspended state
– Entered when a thread’s Suspend method is called – Method Resume returns thread to Started state
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Outline
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namespace provides multithreading capabilities
MessagePrinter.vb Define CMessagePrinter
' constructor to initialize a CMessagePrinter object Determine random Public Sub New()
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• Timeslicing
– Enables threads of equal priority to share a processor – Quantum: a brief burst of processor time – Threads execute for a quantum, then stop
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• Running state
– Operating system assigns a processor to highest priority Started thread – Indicates that a thread has a processor – Running thread’s ThreadStart delegate executes
Print gets string representation for thread CurrentThread currently executing thread = Thread.CurrentThread property Name property Shared method Sleep of Thread class Call to state Sleep puts current thread in WaitSleepJoin for specified number of milliseconds
Shared property CurrentThread ' pick random sleep time between 0 and of Thread class obtains reference to sleepTime = randomObject.Next(5001) End Sub ' New thread currently executing
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• WaitSleepJoin state
– Entered by:
• Calling Monitor method Wait – Thread stops executing until another thread calls Monitor method Pulse or PulseAll • Calling Thread method Sleep – Thread waits a specified number of milliseconds • Calling another thread’s Join method – Thread waits until joined thread terminates
14.3
Thread Priorities and Thread Scheduling
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• Thread priorities
– ThreadPriority enumeration (System.Threading namespace) – By default, threads have priority Normal – Used by thread scheduler to determine when each thread should execute – Lower priority threads do not execute until all higher priority threads terminate
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Start Started
quantum expiration
Running
dispatch (assign a processor)
WaitSleepJoin
Suspended
Stopped
Blocked
Resume
Fig. 14.1 Thread life cycle.