Several ways for Linux processes to communicate with each other

First: Pipeline communication.

When two processes communicate through a pipeline, the process that sends the information is called the write process; The process that receives the information is called the read process. The intermediate medium of the pipeline communication mode is the file, which is usually called the pipe file, which connects a write process and a read process together like a pipe to achieve communication between the two processes. The write process writes information to the pipeline file through the write end; The read process reads information from the pipeline file through the readout.

The two processes work together to write and read continuously, forming a pipeline for both parties to pass information through the pipeline.

The second type is message buffered communication.

Multiple independent processes can communicate with each other through a message buffering mechanism. The implementation of this communication is based on the message buffer as the intermediate medium, and the sending and receiving operations of both parties to the communication are based on the message. In memory, message buffers are organized into queues, often referred to as message queues.

Once a message queue is created, it can be shared by multiple processes, and the process that sends a message can send any message to the specified message queue at any time and check if there is a receiving process waiting for the message it sends. If so, it wakes up, and the process receiving the message can get the message to the specified message queue when it needs it, and if the message has not arrived, it goes to sleep and wait.

The third type: shared memory communication.

In view of the shortcomings of message buffering, which requires CPU usage for message replication, OS provides a communication method for direct data exchange between processes. Shared memory, as the name suggests, allows multiple processes to communicate with the same memory segment with the support of external communication protocols or synchronous, mutex mechanisms, it is one of the most efficient data communication methods, which is characterized by no intermediate links, and directly maps the shared memory pages to the respective virtual address spaces of the processes that communicate with each other through attachments, so that multiple processes can directly access the same physical memory page.

1 Pipe and named pipe: Pipe can be used for communication between related processes, and named pipe overcomes the limitation of pipe without name, so it allows communication between unrelated processes in addition to the functions that pipes have;

2. Signal: Signal is a more complex communication method, which is used to notify the receiving process that a certain event has occurred, in addition to being used for inter-process communication, the process can also send a signal to the process itself; In addition to supporting UNIX's early signal semantic function Sigal, Linux also supports the signal function SigAction that conforms to the standard semantics (in fact, this function is based on BSD, which re-implements the signal function with the sigaction function in order to achieve a reliable signal mechanism and unify the external interface);

3. Message queue: A message queue is a linked table of messages, including the POSIX message queue System V. Processes with sufficient permissions can add messages to the queue, and processes with read permissions can read away messages from the queue.

Message queues overcome the shortcomings of the small amount of information that signals can carry, the pipeline can only carry unformatted byte streams, and the buffer size is limited.

4 Shared Memory: Enables multiple processes to access the same memory space, which is the fastest form of IPC available. It is designed to deal with the inefficiency 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.

5Semaphore: It is mainly used as a means of synchronization between processes and between different threads of the same process.

6 sockets: A more general inter-process communication mechanism that can be used for inter-process communication between different machines. Originally developed by the BSD branch of the Unix system, it can now be ported to other Unix-like systems

Both Linux and System V variants support sockets.

Inter-process communicationInter-process communication is the transmission or exchange of information between different processes, the user space of the process is independent of each other, and the process can use the system space to exchange information.

A pipe is a half-duplex method of communication where data can only flow in one direction. If you want to have duplex communication, you need to establish two pipes.

Pipelines can only be used between processes that are related, such as parent-child or sibling processes.

Named

pipe) is also a duplex mode of communication, but it allows for unrelated inter-process use.

Semophore

A semaphore is often used as a locking mechanism, which is a counter that controls access to a shared resource by multiple processes, preventing multiple processes from accessing a shared resource at the same time. Semaphores are mainly used as a means of synchronization between processes or between different threads of the same process.

Signal (sinal).

Signaling is a more complex communication method used to notify the receiving process that certain events have occurred, and it is necessary to pay attention to whether the function called in signal processing is signal-safe.

Message queue (message

queue)

A message queue is a linked list of messages that is stored in the kernel and identified by a message queue identifier.

Shared memory (shared

memory)

Shared memory is a piece of memory that is accessed by other processes, created by a single process, and accessible by multiple processes. Shared memory is the fastest IPC method, and it is specifically designed to address the low operational efficiency of other inter-process communication methods. It is often used in conjunction with other communication mechanisms, such as semaphores, to enable synchronization and communication between processes.

Sockets

Sockets are also a way of inter-process communication, and unlike other methods, it can be used for process communication between different hosts (which is also its primary purpose).

Disadvantages of several ways.

Pipelines: Slow, limited capacity, and can only be used for kinship interprocess communication.

Named Pipeline: Same pipe, but allows unrelated inter-process communication.

Message queue: The capacity is limited by the system, and data will be left in the queue, so the unread data should be taken into account when reading.

Semaphore: Mainly used for synchronization, it cannot transmit complex data information.