ericltw
commented
6 years ago Single threading
In computer programming, single-threading is the processing of one command at a time. The opposite of single-threading is multithreading.
Multithreading
Multithreading is mainly found in multitasking operating system. Multithreading is widespread programming and execution model that allows multiple threads to exist within the context of one process. These threads share the process's resource, but are able to execute independently. The threaded programming model provides developers with a useful abstraction of concurrent execution. Multithreading can also be applied to one process to enable parallel execution on a multiprocessing system.
Multithreaded applications have the following advantages:
- Responsiveness: multithreading can allow an application to remain responsive to input.
- Fast execution: this advantage of the multithreaded program allows it to operate faster on computer system that have multiple CPUs or one or more multi-core processors, or across a cluster of machine, because the threads of the program naturally lend themselves to parallel execution, assuming sufficient independence (that the don't need to wait each other).
- Lower resource consumption: using threads, an application can serve multiple clients concurrently using fewer resource than it would need when using multiple process copies of itself. For example, the Apache HTTP server uses thread pools: a pool of listener threads for listening to incoming request, and pool of server threads for processing those requests.
- Better system utilization: as an example, a file system using multiple threads can achieve higher throughput and lower latency since data in a faster medium (such as cache memory) can be retrieve by one thread while another thread retrieves data from a slower medium (such as external storage) with neither thread waiting for the other to finish.
- Simplified sharing and communication: unlike processes, which require a message passing or shared memory mechanism to perform inter-process communication, threads can communication through data, code and files they already share.
- Parallelization: applications looking to use multicore or multi-CPU systems can use multithreading to split data and tasks into parallel subtasks and let the underlying architecture manage how the threads run, either concurrently on one core or in parallel on multiple cores.
Multithreading has the following drawbacks:
- Synchronization: since threads share the same address space, the programmer must be careful to avoid race conditions and other non-intuitive behaviors. In order for data be correctly manipulated, threads will often need to rendezvous in time in order to process the data in the correct order. Threads may also require mutually exclusive operations in order to prevent common data form being simultaneously modified or read while in the process of being modified. Careless use of such primitives can lead to deadlocks , livelocks or races over a resource.
- Thread crashes a process: an illegal operation performed by a thread crashes the entire process; therefore, one misbehaving thread can disrupt the processing of all the other threads in the application.
What is a program
Program is an executable file containing the set of instructions written to perform a specific job on your computer. For example, chrome.exe is an executable file containing the set of instructions written so that we can view web pages. notpad.exe is an executable file containing the set of instructions which help us to edit and print the text files.
What is a process
Process is an executing instance of a program. For example, when you double click on Google Chrome icon on your computer, you start a process which will run the Google Chrome program. When you double click on a notepad icon on your computer, a process is started that will run the notepad program.
A process is sometimes refereed as active entity as it resides on the primary memory and leaves the memory if the system is rebooted. Several process may related to same program. For example, you can run multiple instance of a notepad program. Each instance is referred as a process.
What is a thread
Thread is the smallest executable unit of a process. For example, when you run a notepad program, operating system creates a process and starts the execution of main thread of the process.
A process can have multiple threads. Each thread will have their own task and own path of execution in a process. For example, in a notepad program, one thread will be taking user inputs and another thread will be printing a document.
All threads of the same process share memory of the that process. As threads of the same process share the same memory, communication between the threads is fast.
Processes and threads can be represented like below,
Process vs Thread
Reference