Silberschatz, Galvin and Gagne  Operating System Concepts Chapter 5: Threads Overview Multithreading Models Threading Issues Pthreads Solaris 2 Threads Windows 2000 Threads Linux Threads Java Threads

Silberschatz, Galvin and Gagne  Operating System Concepts Single and Multithreaded Processes

Silberschatz, Galvin and Gagne  Operating System Concepts Benefits Responsiveness Resource Sharing Economy Utilization of MP Architectures

Silberschatz, Galvin and Gagne  Operating System Concepts User Threads Thread management done by user-level threads library Examples - POSIX Pthreads - Mach C-threads - Solaris threads

Silberschatz, Galvin and Gagne  Operating System Concepts Kernel Threads Supported by the Kernel Examples - Windows 95/98/NT/ Solaris - Tru64 UNIX - BeOS - Linux

Silberschatz, Galvin and Gagne  Operating System Concepts Multithreading Models Many-to-One One-to-One Many-to-Many

Silberschatz, Galvin and Gagne  Operating System Concepts Many-to-One Many user-level threads mapped to single kernel thread. Used on systems that do not support kernel threads.

Silberschatz, Galvin and Gagne  Operating System Concepts Many-to-One Model

Silberschatz, Galvin and Gagne  Operating System Concepts One-to-One Each user-level thread maps to kernel thread. Examples - Windows 95/98/NT/ OS/2

Silberschatz, Galvin and Gagne  Operating System Concepts One-to-one Model

Silberschatz, Galvin and Gagne  Operating System Concepts 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. Solaris 2 Windows NT/2000 with the ThreadFiber package

Silberschatz, Galvin and Gagne  Operating System Concepts Many-to-Many Model

Silberschatz, Galvin and Gagne  Operating System Concepts Threading Issues Semantics of fork() and exec() system calls. Thread cancellation. Signal handling Thread pools Thread specific data

Silberschatz, Galvin and Gagne  Operating System Concepts The fork and exec system calls Two versions of fork()  Duplicates all threads: not necessary if exec is called immediately  Duplicates only the thread that invoked the fork system call

Silberschatz, Galvin and Gagne  Operating System Concepts Thread cancellation Task of terminating a thread before is has completed Two different scenarios:  Asynchronous cancellation  Deferred cancellation Difficulty occurs when:  Resources have been allocated to a cancelled thread  While the cancelled thread is updating shared data Problems can be alleviated with deferred cancellation at cancellation point

Silberschatz, Galvin and Gagne  Operating System Concepts Signal Handling A signal is used to notify a process that a particular event has occurred. e.g. divide by zero, illegal memory access A signal can be received:  Synchronously: delivered to the process causing the signal  Asynchronously: generated by an external event Signal pattern:  A signal is generated by the occurrence of a particular event  A generated signal is delivered to a process  Once delivered, the signal must be handled Handler:  Default signal handler  User-defined handler

Silberschatz, Galvin and Gagne  Operating System Concepts Signal Handling Where should a signal be delivered: (depend on signal type)  Thread to which the signal applies  Every thread in the process  Certain thread in the process  A specific thread assigned (APC)

Silberschatz, Galvin and Gagne  Operating System Concepts Thread Pools Creating a separate thread is superior than creating a separate process when a server receiving a request:  Less time for creating thread  However, unlimited threads could exhaust system resources Thread Pools: to create a number of threads at process startup and place them into a pool If the pool contains no available thread, the server waits until one becomes free

Silberschatz, Galvin and Gagne  Operating System Concepts Thread-Specific Data Each thread needs its own copy of certain data in some circumstances

Silberschatz, Galvin and Gagne  Operating System Concepts Pthreads a POSIX standard (IEEE 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.

Silberschatz, Galvin and Gagne  Operating System Concepts Solaris 2 Threads

Silberschatz, Galvin and Gagne  Operating System Concepts Solaris Process

Silberschatz, Galvin and Gagne  Operating System Concepts Windows 2000 Threads Implements the one-to-one mapping. Each thread contains - a thread id - register set - separate user and kernel stacks - private data storage area

Silberschatz, Galvin and Gagne  Operating System Concepts Linux 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)

Silberschatz, Galvin and Gagne  Operating System Concepts Java Threads Java threads may be created by:  Extending Thread class  Implementing the Runnable interface Java threads are managed by the JVM.

Silberschatz, Galvin and Gagne  Operating System Concepts Java Thread States