Chapter 4 Threads Operating System Concepts with Java

Chapter 4: Threads p p p p Overview Multithreading Models Threading Issues Pthreads Windows

Single and Multithreaded Processes Operating System Concepts with Java – 7 th Edition, Nov

Benefits p Responsiveness p Resource Sharing p Economy p Utilization of MP Architectures Operating

Excursion: Programming Models p p UI and network programs have multiple event sources n

User and Kernel Threads p User threads - Thread management done by user-level threads

Kernel Threads Examples n Windows XP/2000 n Solaris n Linux n Tru 64 UNIX

Multithreading Models Mapping user threads to kernel threads: p Many-to-One p One-to-One p Many-to-Many

Many-to-One p p Many user-level threads mapped to single kernel thread Examples: n Solaris

Many-to-One Model Operating System Concepts with Java – 7 th Edition, Nov 15, 2006

One-to-One p p Each user-level thread maps to kernel thread Examples n Windows NT/XP/2000

One-to-one Model Operating System Concepts with Java – 7 th Edition, Nov 15, 2006

Many-to-Many Model p p Allows many user level threads to be mapped to many

Many-to-Many Model Operating System Concepts with Java – 7 th Edition, Nov 15, 2006

Two-level Model p p Similar to M: M, except that it allows a user

Two-level Model Operating System Concepts with Java – 7 th Edition, Nov 15, 2006

Java Threads p Java threads are managed by the JVM p Java threads may

Java Threads - Example Program Operating System Concepts with Java – 7 th Edition,

Java Thread States Operating System Concepts with Java – 7 th Edition, Nov 15,

Java Threads - Producer-Consumer Operating System Concepts with Java – 7 th Edition, Nov

Threading Issues p p p Semantics of fork() and exec() system calls Thread cancellation

Semantics of fork() and exec() p Does fork() duplicate only the calling thread or

Thread Cancellation p p Terminating a thread before it has finished Two general approaches:

Thread Cancellation Deferred cancellation in Java Interrupting a thread Operating System Concepts with Java

Thread Cancellation Deferred cancellation in Java Checking interruption status Operating System Concepts with Java

Signal Handling p p p Signals are used in UNIX systems to notify a

Unix signal handling: asynchronous #include <signal. h> #include <stdio. h> void sigint(int sig) {

Unix signal handling: synchronous #include <signal. h> <setjmp. h> <stdio. h> <unistd. h> int

Signal advice p p p p Very similar to interrupt handlers Keep signal handlers

Thread Pools p p Create a number of threads in a pool where they

Thread Pools p Java provides 3 thread pool architectures: 1. Single thread executor -

Thread Pools A task to be serviced in a thread pool Operating System Concepts

Thread Pools Creating a thread pool in Java Operating System Concepts with Java –

Thread Specific Data p p Allows each thread to have its own copy of

Thread Specific Data Thread-specific data in Java. Operating System Concepts with Java – 7

Scheduler Activations p p p Both M: M and Two-level models require communication to

Pthreads p p p A POSIX standard (IEEE 1003. 1 c) API for thread

Windows XP Threads p p p Implements the one-to-one mapping Each thread contains n

Windows XP Threads Operating System Concepts with Java – 7 th Edition, Nov 15,

Linux Threads p p p Linux refers to them as tasks rather than threads

End of Chapter 4 Operating System Concepts with Java – 7 th Edition, Nov

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Chapter 4: Threads p p p p Overview Multithreading Models Threading Issues Pthreads Windows XP Threads Linux Threads Java Threads Operating System Concepts with Java – 7 th Edition, Nov 15, 2006 4. 2 Silberschatz, Galvin and Gagne © 2007

Excursion: Programming Models p p UI and network programs have multiple event sources n network packets, user input, media input (audio/video) Can never block: n event-based --> finite-state machine p only very short, non-blocking fragments p asynchronous system calls p start, wait for event, transition n thread-based p block for each logical thread of execution § naturally sequential operations § can’t read web page until domain name has been resolved Operating System Concepts with Java – 7 th Edition, Nov 15, 2006 4. 5 read URL sho w erro r query DNS receive response open socket connect succeeds send request receive response display page Silberschatz, Galvin and Gagne © 2007

User and Kernel Threads p User threads - Thread management done by user-level threads library. p Kernel threads - Threads directly supported by the kernel. Operating System Concepts with Java – 7 th Edition, Nov 15, 2006 4. 6 Silberschatz, Galvin and Gagne © 2007

Multithreading Models Mapping user threads to kernel threads: p Many-to-One p One-to-One p Many-to-Many Operating System Concepts with Java – 7 th Edition, Nov 15, 2006 4. 8 Silberschatz, Galvin and Gagne © 2007

Many-to-One p p Many user-level threads mapped to single kernel thread Examples: n Solaris Green Threads n GNU Portable Threads Operating System Concepts with Java – 7 th Edition, Nov 15, 2006 4. 9 Silberschatz, Galvin and Gagne © 2007

One-to-One p p Each user-level thread maps to kernel thread Examples n Windows NT/XP/2000 n Linux n Solaris 9 and later Operating System Concepts with Java – 7 th Edition, Nov 15, 2006 4. 11 Silberschatz, Galvin and Gagne © 2007

Many-to-Many Model p p 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 Thread. Fiber package Operating System Concepts with Java – 7 th Edition, Nov 15, 2006 4. 13 Silberschatz, Galvin and Gagne © 2007

Two-level Model p p Similar to M: M, except that it allows a user thread to be bound to kernel thread Examples n IRIX n HP-UX n Tru 64 UNIX n Solaris 8 and earlier Operating System Concepts with Java – 7 th Edition, Nov 15, 2006 4. 15 Silberschatz, Galvin and Gagne © 2007

Java Threads p Java threads are managed by the JVM p Java threads may be created by: n Implementing the Runnable interface Operating System Concepts with Java – 7 th Edition, Nov 15, 2006 4. 17 Silberschatz, Galvin and Gagne © 2007

Threading Issues p p p Semantics of fork() and exec() system calls Thread cancellation Signal handling Thread pools Thread specific data Scheduler activations Operating System Concepts with Java – 7 th Edition, Nov 15, 2006 4. 24 Silberschatz, Galvin and Gagne © 2007

Semantics of fork() and exec() p Does fork() duplicate only the calling thread or all threads? Operating System Concepts with Java – 7 th Edition, Nov 15, 2006 4. 25 Silberschatz, Galvin and Gagne © 2007

Thread Cancellation p p Terminating a thread before it has finished Two general approaches: n Asynchronous cancellation terminates the target thread immediately n Deferred cancellation allows the target thread to periodically check if it should be cancelled Operating System Concepts with Java – 7 th Edition, Nov 15, 2006 4. 26 Silberschatz, Galvin and Gagne © 2007

Signal Handling p p p 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: n Deliver the signal to the thread to which the signal applies n Deliver the signal to every thread in the process n Deliver the signal to certain threads in the process n Assign a specific threa to receive all signals for the process Operating System Concepts with Java – 7 th Edition, Nov 15, 2006 4. 29 Silberschatz, Galvin and Gagne © 2007

Unix signal handling: asynchronous #include <signal. h> #include <stdio. h> void sigint(int sig) { printf("signal handler %dn", sig); /* re-set the signal handler again for next time */ signal(SIGINT, sigint); } int main(int argc, char *argv[]) { signal(SIGINT, sigint); while (1) { sleep(5); } } Operating System Concepts with Java – 7 th Edition, Nov 15, 2006 4. 30 Silberschatz, Galvin and Gagne © 2007

Unix signal handling: synchronous #include <signal. h> <setjmp. h> <stdio. h> <unistd. h> int div; static jmp_buf env; void sigfpe(int sig) { printf("signal handler %dn", sig); div = 2; siglongjmp(env, 1); } int main(int argc, char *argv[]) { int x = 42; signal(SIGFPE, sigfpe); printf("before divisionn"); div = 0; if (sigsetjmp(env, 0) != 0) { printf("we tried to divide by zero: %d! n", div); } x /= div; printf("after division: %d %dn", x, div); return 0; } Operating System Concepts with Java – 7 th Edition, Nov 15, 2006 4. 31 Silberschatz, Galvin and Gagne © 2007

Signal advice p p p p Very similar to interrupt handlers Keep signal handlers short Mask signals to avoid signal-in-signal n sigprocmask() Use fault signals for cleanup, not fixup n SIGBUS, SIGSEGV, SIGFPE Can only use a single alarm() timer n need timer manager otherwise Signals are relatively slow n lots of context switches n asynchronous I/O Don’t rely on restart too much Avoid longjmp() Operating System Concepts with Java – 7 th Edition, Nov 15, 2006 4. 32 Silberschatz, Galvin and Gagne © 2007

Thread Pools p p Create a number of threads in a pool where they await work Advantages: n Usually slightly faster to service a request with an existing thread than create a new thread n Allows the number of threads in the application(s) to be bound to the size of the pool http: //www-128. ibm. com/developerworks/java/library/j-jtp 0730. html Operating System Concepts with Java – 7 th Edition, Nov 15, 2006 4. 33 Silberschatz, Galvin and Gagne © 2007

Thread Pools p Java provides 3 thread pool architectures: 1. Single thread executor - pool of size 1. 2. Fixed thread executor - pool of fixed size. 3. Cached thread pool - pool of unbounded size Operating System Concepts with Java – 7 th Edition, Nov 15, 2006 4. 34 Silberschatz, Galvin and Gagne © 2007

Thread Specific Data p p 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 with Java – 7 th Edition, Nov 15, 2006 4. 37 Silberschatz, Galvin and Gagne © 2007

Scheduler Activations p p p 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 Operating System Concepts with Java – 7 th Edition, Nov 15, 2006 4. 39 Silberschatz, Galvin and Gagne © 2007

Pthreads p p p A POSIX standard (IEEE 1003. 1 c) 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) Operating System Concepts with Java – 7 th Edition, Nov 15, 2006 4. 40 Silberschatz, Galvin and Gagne © 2007

Windows XP Threads p p p Implements the one-to-one mapping Each thread contains n A thread id n Register set n Separate user and kernel stacks n Private data storage area The register set, stacks, and private storage area are known as the context of the threads Operating System Concepts with Java – 7 th Edition, Nov 15, 2006 4. 41 Silberschatz, Galvin and Gagne © 2007

Linux Threads p p p 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) Operating System Concepts with Java – 7 th Edition, Nov 15, 2006 4. 43 Silberschatz, Galvin and Gagne © 2007