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What is the difference between a Java thread and a process? I believe many inexperienced people are at a loss about it. Therefore, this article summarizes the causes and solutions of the problem. Through this article, I hope you can solve this problem.

I. what is the process

A process is the basic unit of resource allocation (CPU, memory, etc.), and it is an instance of program execution. When the program is running, the system will create a process, allocate resources to it, and then put the process into the process ready queue. When the process scheduler selects it, it will allocate CPU time to it, and the program will actually run. The advantage of the process is to improve the running efficiency of CPU and execute multiple programs at the same time, that is, concurrent execution. But strictly speaking, it is not absolute to execute multiple programs at the same time, but CPU switches between different processes at high speed through scheduling algorithms such as time slices. Processes, similar to human beings, are generated, have long or short effective lives, can produce one or more sub-processes, and will eventually die out. Each child process has only one parent process. By the way, a child process is generated in Linux by calling the fork () function. When a child process is created, it is almost identical to the parent process. It comes from the address space of the parent process, copy. Although they can share pages with program code, they each have their own data space. Changes to the child process's memory do not affect the parent process, and vice versa.

What is a thread

Thread is an execution path, which is the smallest unit of program execution. It is an execution flow of a process and the basic unit of CPU scheduling and dispatching. A process can be composed of many threads. All resources of the process are shared among threads, and each thread has its own stack and local variables. Threads are independently scheduled and executed by CPU, which allows multiple threads to run at the same time in a multi-CPU environment. Similarly, multithreading can also implement concurrent operations, allocating one thread for each request. A thread is a path that can be executed. Multithreading means that multiple execution paths are executed at the same time (in parallel).

Third, the characteristics of threads and processes (1) process characteristics:

1: independence: a process is an independent entity in the system, it can own resources independently, each process has its own independent address space, without the operation of the process itself, the user process can not directly access the address space of other processes.

2: dynamic: the difference between a process and a program is that the process is dynamic, there is a concept of time in the process, and the process has its own life cycle and different states.

3: concurrency: multiple processes can be executed concurrently on a single processor without affecting each other.

(2) Thread characteristics

1: lightweight entity

The entity units in the thread basically do not own the system resources, but there are only a few essential resources that can run independently. The entities of a thread include programs, data, and TCB. Thread is a dynamic concept, and its dynamic characteristics are described by thread control block TCB.

2: the basic unit of independent scheduling and dispatch

In multi-thread OS, thread is the basic unit that can run independently, so it is also the basic unit of independent scheduling and dispatching. However, because threads are "light", thread switching is very fast and inexpensive (in a unified process).

3: can be executed concurrently

Multiple threads in a process can be executed concurrently, even allowing all threads in a process to execute concurrently; similarly, threads in different processes can execute concurrently, making full use of and giving full play to the ability of processors and peripherals to work in parallel.

4: share process resources

All threads in the same process can share the resources owned by the process, first of all, all threads have the same address space (the address space of the process), which means that the thread can access each virtual address in the address space; in addition, it can also access the open files, timers, semaphore mechanisms owned by the process, and so on. Because threads within the same process share memory and files, threads do not have to call the kernel to communicate with each other.

Fourth, the difference between processes and threads:

1. It is easy to create new threads. However, creating a new process requires repeating the parent process.

2. Threads can control other threads of the same process. The process cannot control the sibling process, only its child process.

3. The process has its own memory space. The thread uses the memory space of the process and shares it with other threads of the process; instead of giving each thread a separate bit of space in the process.

4. Threads (in the same process) run in a shared memory space, while processes run in a different memory space.

5. Threads can use wait (), notify (), notifyAll () and other methods to communicate directly with other threads (the same process); however, processes need to use "inter-process communication" (IPC) to communicate with other processes in the operating system.

After reading the above, have you mastered the method of what is the difference between Java threads and processes? If you want to learn more skills or want to know more about it, you are welcome to follow the industry information channel, thank you for reading!

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