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A process with two threads of execution, running on one processor Program vs. Process vs. Thread Scheduling, Preemption, Context Switching. In computer science, a thread of execution is the smallest sequence of programmed instructions that can be managed independently by a scheduler, which is typically a part of the operating system. [1]
Thread scheduling is also a major problem in multithreading. Merging data from two processes can often incur significantly higher costs compared to processing the same data on a single thread, potentially by two or more orders of magnitude due to overheads such as inter-process communication and synchronization. [2] [3] [4]
The TCB is "the manifestation of a thread in an operating system." Each thread has a thread control block. An operating system keeps track of the thread control blocks in kernel memory. [2] An example of information contained within a TCB is: Thread Identifier: Unique id (tid) is assigned to every new thread; Stack pointer: Points to thread's ...
For instance, to handle an IF-ELSE block where various threads of a processor execute different paths, all threads must actually process both paths (as all threads of a processor always execute in lock-step), but masking is used to disable and enable the various threads as appropriate. Masking is avoided when control flow is coherent for the ...
In a multiprocessor system, task parallelism is achieved when each processor executes a different thread (or process) on the same or different data. The threads may execute the same or different code. In the general case, different execution threads communicate with one another as they work, but this is not a requirement.
However, in a multitasking operating system, the operating system switches between processes or threads to allow the execution of multiple processes simultaneously. [2] For every switch, the operating system must save the state of the currently running process, followed by loading the next process state, which will run on the CPU.
Concurrent data structures are significantly more difficult to design and to verify as being correct than their sequential counterparts. The primary source of this additional difficulty is concurrency, exacerbated by the fact that threads must be thought of as being completely asynchronous: they are subject to operating system preemption, page faults, interrupts, and so on.
In 2010, IBM released systems based on the POWER7 processor with eight cores with each having four Simultaneous Intelligent Threads. This switches the threading mode between one thread, two threads or four threads depending on the number of process threads being scheduled at the time.