Shulou(Shulou.com)06/02 Report--

This article introduces the relevant knowledge of "the difference between Linux thread and process and its communication mode". In the operation of actual cases, many people will encounter such a dilemma. Next, let the editor lead you to learn how to deal with these situations! I hope you can read it carefully and be able to achieve something!

Concept

Thread: the smallest unit that the operating system can schedule operations. Is an execution process in a process that can run multiple threads in a process.

Process: an instance of an executing program.

The difference between process and thread

A program has at least one process, and a process has at least one thread.

The division scale of threads is smaller than that of processes, which makes multithreaded programs have high concurrency.

In addition, the process has an independent memory unit during execution, and multiple threads share memory, which greatly improves the running efficiency of the program.

There is a difference between a thread and a process during execution. Each independent thread has an entrance to the program, a sequential execution sequence, and an exit to the program.

However, threads cannot execute independently and must be stored in the application, which provides multiple thread execution control.

From a logical point of view, the significance of multithreading is that there are multiple execution parts in an application that can be executed at the same time.

However, the operating system does not regard multiple threads as multiple independent applications to achieve process scheduling and management and resource allocation. This is the important difference between processes and threads.

A process is a running activity of a program with a certain independent function on a certain data set, and a process is an independent unit of resource allocation and scheduling in the system.

A thread is an entity of a process and the basic unit of CPU scheduling and dispatching. It is a smaller basic unit that can run independently than a process.

The thread itself basically does not own system resources, only a few resources that are essential to running (such as program counters, a set of registers and stacks), but it can share all the resources owned by the process with other threads belonging to the same process.

One thread can create and undo another thread; multiple threads in the same process can execute concurrently.

Summary:

The main difference between processes and threads is that they are different ways of managing operating system resources.

A process has an independent address space. After a process crashes, it will not affect other processes in protected mode, and threads are just different execution paths in a process.

Threads have their own stacks and local variables, but there is no separate address space between threads, so the death of a thread equals the death of the whole process, so a multi-process program is more robust than a multi-thread program, but when a process is switched, it consumes more resources and is less efficient.

However, for some concurrent operations that require simultaneous and shared variables, only threads can be used, not processes.

If you are interested in going deeper, I suggest you take a look at "Modern operating system" or "Design and implementation of operating system". Yeah, just one question.

Interprocess communication

Brief introduction of several main means of inter-process communication under linux:

Pipes (Pipe) and named pipes (named pipe): pipes can be used for communication between related processes. Named pipes overcome the limitation that pipes do not have names, so in addition to the functions of pipes, they also allow communication between unrelated processes.

Signal (Signal): a signal is a complex mode of communication that notifies the receiving process that an event has occurred. In addition to being used for inter-process communication, the process can also send signals to the process itself. Linux not only supports the early signal semantic function sigal of Unix, but also supports the signal function sigaction which semantically conforms to the Posix.1 standard (in fact, this function is based on BSD. In order to realize the reliable signal mechanism and unify the external interface, BSD uses the sigaction function to re-implement the signal function).

Message queuing (Message): message queuing is a linked list of messages, including Posix message queuing system V message queues. Processes with sufficient permissions can add messages to the queue, and processes that are given read permission can read away messages from the queue. Message queue overcomes the shortcomings that the signal carries less information, the pipeline can only carry unformatted byte flow and the buffer size is limited.

Shared memory: allows multiple processes to access the same memory space, which is the fastest available IPC form. It is designed for the low efficiency of other communication mechanisms. It is often used in conjunction with other communication mechanisms, such as semaphores, to achieve synchronization and mutual exclusion between processes.

Semaphores (semaphore): mainly used as a means of synchronization between processes and between different threads of the same process.

Socket (Socket): a more general mechanism for inter-process communication that can be used for inter-process communication between different machines. Originally developed by the BSD branch of the Unix system, it is now generally portable to other types of Unix systems: both Linux and System V variants support sockets.

Comparison, advantages and disadvantages of various modes of communication:

Pipes: slow speed, limited capacity, and only parent-child processes can communicate

Named named pipe: any process can communicate, but the speed is slow

Message queue: the capacity is limited by the system, and you should pay attention to the problem that you didn't finish reading the data last time when you read it for the first time.

Semaphores: complex messages cannot be passed, they can only be used for synchronization

Shared memory: the capacity can be easily controlled and the speed is fast, but keep synchronized. For example, when one process is writing, another process should pay attention to the problem of reading and writing, which is equivalent to thread safety in threads. Of course, the shared memory area can also be used for inter-thread communication, but this is not necessary. Threads already share a piece of memory within the same process.

Inter-thread communication

By accessing shared variables (Note: synchronization issues need to be addressed)

Flow through pipe

This is the end of the content of "the difference between Linux threads and processes and how they communicate". Thank you for reading. If you want to know more about the industry, you can follow the website, the editor will output more high-quality practical articles for you!

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.