Upload
jennifer-morgan
View
252
Download
6
Tags:
Embed Size (px)
Citation preview
Chapter 4: ThreadsChapter 4: Threads
Adapted to COP4610 by Robert van Engelen
4.2 Silberschatz, Galvin and Gagne ©2005Operating System Concepts – 7th edition, Jan 23, 2005
Process Versus ThreadProcess Versus Thread
A process has its own address space, file descriptors of open files and devices, and other resources
fork() duplicates the process
A single process can have a single thread of control or multiple threads
A new thread can be started at any time
Each thread shares the same data, file descriptors, and code of the process
A thread has its own registers, stack (for function calls), and program counter
4.3 Silberschatz, Galvin and Gagne ©2005Operating System Concepts – 7th edition, Jan 23, 2005
Single and Multithreaded ProcessesSingle and Multithreaded Processes
4.4 Silberschatz, Galvin and Gagne ©2005Operating System Concepts – 7th edition, Jan 23, 2005
BenefitsBenefits
Benefits of multi-threading Responsiveness (e.g. main thread executes while
another waits for I/O) Resource sharing Economy (threads are cheap compared to processes) Utilization of MP architectures
For example, one thread of a Web browser renders the content of a page while another downloads data
4.5 Silberschatz, Galvin and Gagne ©2005Operating System Concepts – 7th edition, Jan 23, 2005
User ThreadsUser Threads
Thread management done by user-level threads library
Three primary thread libraries:
POSIX Pthreads
Win32 threads
Java threads
4.6 Silberschatz, Galvin and Gagne ©2005Operating System Concepts – 7th edition, Jan 23, 2005
Kernel ThreadsKernel Threads
Supported by the Kernel
Examples
Windows XP/2000
Solaris
Linux
Tru64 UNIX
Mac OS X
4.7 Silberschatz, Galvin and Gagne ©2005Operating System Concepts – 7th edition, Jan 23, 2005
Multithreading ModelsMultithreading Models
Many-to-One
One-to-One
Many-to-Many
4.8 Silberschatz, Galvin and Gagne ©2005Operating System Concepts – 7th edition, Jan 23, 2005
Many-to-OneMany-to-One
Many user-level threads mapped to single kernel thread
Examples:
Solaris Green Threads
GNU Portable Threads
4.9 Silberschatz, Galvin and Gagne ©2005Operating System Concepts – 7th edition, Jan 23, 2005
One-to-OneOne-to-One
Each user-level thread maps to kernel thread
Examples
Windows NT/XP/2000
Linux
Solaris 9 and later
4.10 Silberschatz, Galvin and Gagne ©2005Operating System Concepts – 7th edition, Jan 23, 2005
Many-to-Many ModelMany-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
Solaris prior to version 9
Windows NT/2000 with the ThreadFiber package
4.11 Silberschatz, Galvin and Gagne ©2005Operating System Concepts – 7th edition, Jan 23, 2005
Two-level ModelTwo-level Model
Similar to M:M, except that it allows a user thread to be bound to kernel thread
Examples
IRIX
HP-UX
Tru64 UNIX
Solaris 8 and earlier
4.12 Silberschatz, Galvin and Gagne ©2005Operating System Concepts – 7th edition, Jan 23, 2005
Threading IssuesThreading Issues
Semantics of fork() and exec() system calls
Thread cancellation
Signal handling
Thread pools
Thread specific data
Scheduler activations
4.13 Silberschatz, Galvin and Gagne ©2005Operating System Concepts – 7th edition, Jan 23, 2005
Semantics of fork() and exec()Semantics of fork() and exec()
Does fork() duplicate only the calling thread or all threads?
Some systems provide two versions of fork
One that copies all threads
One that creates a process with a single thread
4.14 Silberschatz, Galvin and Gagne ©2005Operating System Concepts – 7th edition, Jan 23, 2005
Thread CancellationThread Cancellation
Terminating a thread before it has finished
Two general approaches:
Asynchronous cancellation one thread terminates the target thread immediately
Deferred cancellation allows the target thread to periodically check a flag if it should be cancelled
Allows a thread to cancel at a safe point, called a cancellation point in Pthreads
4.15 Silberschatz, Galvin and Gagne ©2005Operating System Concepts – 7th edition, Jan 23, 2005
Signal HandlingSignal Handling
Signals are used in UNIX systems to notify a process that a particular event has occurred (e.g. control-C)
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
4.16 Silberschatz, Galvin and Gagne ©2005Operating System Concepts – 7th edition, Jan 23, 2005
Thread PoolsThread Pools
Create a number of threads in a pool where they await work
With more work than threads, work is queued until a thread fetches it from the queue
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
4.17 Silberschatz, Galvin and Gagne ©2005Operating System Concepts – 7th edition, Jan 23, 2005
Thread Specific DataThread 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)
4.18 Silberschatz, Galvin and Gagne ©2005Operating System Concepts – 7th edition, Jan 23, 2005
Scheduler ActivationsScheduler Activations
Both M:M and two-level models require communication to maintain the appropriate number of kernel threads allocated to the application
Scheduler activations provide upcalls - a communication mechanism from the kernel to the thread library
This communication allows an application to maintain the correct number kernel threads
4.19 Silberschatz, Galvin and Gagne ©2005Operating System Concepts – 7th edition, Jan 23, 2005
PthreadsPthreads
A POSIX standard (IEEE 1003.1c) API for thread creation and synchronization
API specifies behavior of the thread library, implementation is up to development of the library
Common in UNIX operating systems (Solaris, Linux, Mac OS X)
4.20 Silberschatz, Galvin and Gagne ©2005Operating System Concepts – 7th edition, Jan 23, 2005
C Pthread ExampleC Pthread Example#include <pthread.h>#include <stdio.h>int sum; /* this data is shared by the thread(s) */void *runner(void *param); /* the thread code, see next slide */
int main(int argc, char *argv[]){ pthread_t tid; /* the thread identifier */ pthread_attr_t attr; /* set of attributes for the thread */ int stat; /* the thread exit value */ if (argc != 2) { fprintf(stderr,"usage: a.out <integer value>\n"); return -1; /* causes exit(-1); */ } if (atoi(argv[1]) < 0) { fprintf(stderr,"Argument %d must be non-negative\n",atoi(argv[1])); return -1; /* causes exit(-1); */ } pthread_attr_init(&attr); /* get the default attributes */ pthread_create(&tid,&attr,runner,argv[1]); /* create the thread */ pthread_join(tid,&stat); /* now wait for the thread to exit */ printf("sum = %d\n",sum);}
4.21 Silberschatz, Galvin and Gagne ©2005Operating System Concepts – 7th edition, Jan 23, 2005
C Pthread Example (cont’d)C Pthread Example (cont’d)
/* The thread will begin control in this function */void *runner(void *param){ int i, upper = atoi(param); sum = 0; if (upper > 0) { for (i = 1; i <= upper; i++) sum += i; } pthread_exit(0); /* exit the thread with status 0 */ }
4.22 Silberschatz, Galvin and Gagne ©2005Operating System Concepts – 7th edition, Jan 23, 2005
Windows XP ThreadsWindows XP Threads
Implements the one-to-one mapping
Each thread contains
A thread id
Register set
Separate user and kernel stacks
Private data storage area
The register set, stacks, and private storage area are known as the context of the threads
The primary data structures of a thread include:
ETHREAD (executive thread block)
KTHREAD (kernel thread block)
TEB (thread environment block)
4.23 Silberschatz, Galvin and Gagne ©2005Operating System Concepts – 7th edition, Jan 23, 2005
Linux ThreadsLinux Threads
Linux refers to them as tasks rather than threads
Thread creation is done through clone() system call
clone() allows a child task to share the address space of the parent task (process)
Linux also supports Pthreads
4.24 Silberschatz, Galvin and Gagne ©2005Operating System Concepts – 7th edition, Jan 23, 2005
Java ThreadsJava Threads
Java threads are managed by the JVM
Java threads may be created by:
Extending Thread class
Implementing the Runnable interface
4.25 Silberschatz, Galvin and Gagne ©2005Operating System Concepts – 7th edition, Jan 23, 2005
Java Thread States Java Thread States
End of Chapter 4End of Chapter 4