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Transcript
Chapter 4: Threads
Chapter 4: Threads
 Overview
 Multithreading Models
 Threading Issues
 Java Threads
Operating System Concepts – 7th edition, Jan 23, 2005
4.2
Silberschatz, Galvin and Gagne ©2005
Single and Multithreaded Processes
A Thread is a lightweight process
Operating System Concepts – 7th edition, Jan 23, 2005
4.3
Silberschatz, Galvin and Gagne ©2005
Examples
 Word program
 Web servers
Operating System Concepts – 7th edition, Jan 23, 2005
4.4
Silberschatz, Galvin and Gagne ©2005
Benefits
 Responsiveness
 Resource Sharing
 Economy

Creation

Context switch
 Utilization of Multiprocessor Architectures
Operating System Concepts – 7th edition, Jan 23, 2005
4.5
Silberschatz, Galvin and Gagne ©2005
User Threads
 Thread management done by user-level threads library
 Library provides support for thread creation scheduling and
managing with no support from kernel
 User thread is fast to create and manage
 Drawback

If the kernel is single thread then any blocking system call will cause
the entire process to block
Operating System Concepts – 7th edition, Jan 23, 2005
4.6
Silberschatz, Galvin and Gagne ©2005
Kernel Threads
 Supported by the Kernel
 Kernel threads is slower to create and manage than user threads
 If a thread performs a blocking system call, the kernel can schedule
another thread
 The kernel can schedule threads on different processors.
 Examples

Windows XP/2000

Solaris

Linux
Operating System Concepts – 7th edition, Jan 23, 2005
4.7
Silberschatz, Galvin and Gagne ©2005
Multithreading Models
 Many-to-One
 One-to-One
 Many-to-Many
Operating System Concepts – 7th edition, Jan 23, 2005
4.8
Silberschatz, Galvin and Gagne ©2005
Many-to-One
 Many user-level threads mapped to single kernel thread
Operating System Concepts – 7th edition, Jan 23, 2005
4.9
Silberschatz, Galvin and Gagne ©2005
One-to-One
 Each user-level thread maps to kernel thread
 Examples

Windows NT/XP/2000

Linux

Solaris 9 and later
Operating System Concepts – 7th edition, Jan 23, 2005
4.10
Silberschatz, Galvin and Gagne ©2005
One-to-one Model
• More concurrently
• allow multiple threads to run in parallel on multiprocessor
• high overhead which affect the performance of the system.
Operating System Concepts – 7th edition, Jan 23, 2005
4.11
Silberschatz, Galvin and Gagne ©2005
Many-to-Many Model
 Allows many user level threads to be mapped to many kernel
threads
 Allows the operating system to create a sufficient number of
kernel threads

Depending on the application or machine.
Operating System Concepts – 7th edition, Jan 23, 2005
4.12
Silberschatz, Galvin and Gagne ©2005
Many-to-Many Model
Operating System Concepts – 7th edition, Jan 23, 2005
4.13
Silberschatz, Galvin and Gagne ©2005
Java Threads
 Java threads are managed by the JVM
 Java threads may be created by:

Extending Thread class

Implementing the Runnable interface
Operating System Concepts – 7th edition, Jan 23, 2005
4.14
Silberschatz, Galvin and Gagne ©2005
Operating System Concepts – 7th edition, Jan 23, 2005
4.15
Silberschatz, Galvin and Gagne ©2005
Operating System Concepts – 7th edition, Jan 23, 2005
4.16
Silberschatz, Galvin and Gagne ©2005
Operating System Concepts – 7th edition, Jan 23, 2005
4.17
Silberschatz, Galvin and Gagne ©2005
Operating System Concepts – 7th edition, Jan 23, 2005
4.18
Silberschatz, Galvin and Gagne ©2005
Threading Issues
 Semantics of fork() system call
 Thread cancellation
 Signal handling
 Thread pools
 Thread specific data
Operating System Concepts – 7th edition, Jan 23, 2005
4.19
Silberschatz, Galvin and Gagne ©2005
Semantics of fork() and exec()
 Does fork() duplicate only the calling thread or all threads?
Operating System Concepts – 7th edition, Jan 23, 2005
4.20
Silberschatz, Galvin and Gagne ©2005
Thread Cancellation
 Terminating a thread before it has finished
 Two general approaches:

Asynchronous cancellation terminates the target
thread immediately

Deferred cancellation allows the target thread to
periodically check if it should be cancelled
Operating System Concepts – 7th edition, Jan 23, 2005
4.21
Silberschatz, Galvin and Gagne ©2005
Signal Handling

Signals are used in UNIX systems to notify a process that a
particular event has occurred

A signal handler is used to process signals

1.
Signal is generated by particular event
2.
Signal is delivered to a process
3.
Signal is handled
Options:

Deliver the signal to the thread to which the signal applies

Deliver the signal to every thread in the process

Deliver the signal to certain threads in the process

Assign a specific thread to receive all signals for the
process
Operating System Concepts – 7th edition, Jan 23, 2005
4.22
Silberschatz, Galvin and Gagne ©2005
Thread Pools
 Create a number of threads in a pool where they await work
 Advantages:

Usually slightly faster to service a request with an existing
thread than create a new thread

Allows the number of threads in the application(s) to be
bound to the size of the pool
Operating System Concepts – 7th edition, Jan 23, 2005
4.23
Silberschatz, Galvin and Gagne ©2005
Thread Specific Data
 Allows each thread to have its own copy of data
 Useful when you do not have control over the thread
creation process (i.e., when using a thread pool)
Operating System Concepts – 7th edition, Jan 23, 2005
4.24
Silberschatz, Galvin and Gagne ©2005
End of Chapter 4