Implicit Threading

• Growing in popularity as numbers of threads increase, program correctness more difficult with explicit threads (baso programmers are bad so we use libs cos it gets too complicated)

• Creation and management of threads done by compilers and run-time libraries rather than programmers

Thread Pools

Java Examples

Factory methods for creating new threads in Java:

• 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
  • Separating task to be performed from mechanics of creating task allows different
    strategies for running task i.e.,Tasks could be scheduled to run periodically

Fork-Join

Java Examples

Even more Java

Multiple threads (tasks) are forked, and then joined.

Look at it from left to right (makes more sence)

OpenMP

C++ Example

loop in parallel

• Set of compiler directives and an API for C, C++, FORTRAN

• Provides support for parallel programming in shared-memory environments

• Identifies parallel regions – blocks of code that can run in parallel

#pragma omp parallel // c++

Create as many threads as there are cores

Grand Central Dispatch

• Apple technology for macOS and iOS operating systems

• Extensions to C, C++ and Objective-C languages, API, and run-time library

• Allows identification of parallel sections

• Manages most of the details of threading

• Block is in “^{ }” :
  ˆ{ printf("I am a block"); }

• Blocks placed in dispatch queue
  • Assigned to available thread in thread pool when removed from queue

Types of Dispatch Queue

concurrent – blocks removed in FIFO order but several may be removed at a time

serial – blocks removed in FIFO order, queue is per process, called main queue

Note: Programmers can create additional serial queues within program