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Chapter 4: Threads (Overview (Benefits (Responsiveness, Resource sharing,…

- - - - Solaris green threads
      - GNU portable threads
  - - - Windows
      - Linux
      - Solaris 9 and later
  - - - Solaris prior to version 9
      - Windows with the ThreadFiber package
  - - - IRIX
      - HP-UX
      - Tru64 UNIX
- - - - Some UNIXes have two versions of fork
    - - Usually works as normal
  - - - Default
        
        Kernel runs when handling signal
      - User-defined
        
        can override default
  - - - Asynchronous cancellation
        
        Terminates the target thread immediately
      - Deferred cancellation
        
        Allows the target thread to periodically check if it should be cancelled
- - - - Definition
        
        A system can perform more than one task simultaneously (Multi-core system)
      - Types
        
        Data
        
        Distribute subsets of the same data across multiple cores, same operation on each
        
        Task
        
        Distributing threads across cores, each thread performing unique operation.
    - - Supports more than one task making progress (Single-core system)
  - - - Management done by user-level threads library
      - Primary thread libraries
        
        POSIX Pthreads
        
        Windows threads
        
        Java threads
    - - Supported by the kenel
      - Example
        
        Windows
        
        Solaris
        
        Linux
- - - - Extending thread class
      - Implementing the runnable interface
  - - - Thread pools
        
        Create a number of threads in a pool where they await work
        
        Pros
        
        Slightly faster to service a request with an existing thread than create a new thread
        
        Allows the number of threads in the application to be bound to the size of the pool
        
        Separating task to be performed from mechanics of creating task allows different strategies for running task
      - OpenMP
        
        Set of compiler directives and an API for C, C++, Fortran
        
        Provides support for parallel programming in shared-memory environments
        
        Identifies parallel regions
      - Grand Central Dispatch
        
        Type of dispatch queues
        
        Serial
        
        Blocks removed in FIFO order, queue is per process called main queue
        
        Concurrent
        
        Removed in FIFO order but several may be removed at a time
        
        Apple technology for Mac OS X and iOS OS
- - - - ETHREAD
        
        Includes pointer to process to which thread belongs to KHTREAD in kernel space
        
        Executive thread block
      - KTHREAD
        
        Kernel thread block
        
        Scheduling and sync info, kernel-mode stack
      - TEB
        
        Thread environment block
        
        Thread id, user-mode stack