Discovering the Queues on Linux: A Guide for Beginners（linux查看队列）

Discovering the Queues on Linux: A Guide for Beginners

Linux is an open-source operating system that comes with a variety of advanced features, one of which is the ability to manage queues. Queues are a data structure used to hold and manage data in a specific order. In this guide, we will explore the queues on Linux and how to work with them as a beginner.

Queues come in different types, including message queues, semaphore queues, and shared memory queues. Each queue serves a specific purpose and has its unique characteristics. To get started with Linux queues, let’s explore each of these types.

Message Queues

Message queues are used to exchange data between multiple processes running on a Linux machine. The data exchanged is usually in the form of a message, which can be a string or any other data type. With message queues, the sender process can send a message to a receiver process without the need for common memory space. Message queues are managed by the kernel, and each message has a unique identifier.

To create a message queue, we can use the `msgget()` system call as follows:

#include 
#include 
key_t key = ftok("myfile", 'a');
int msgid = msgget(key, 0666 | IPC_CREAT);

In the example above, `ftok()` is used to generate a unique key based on a file and a character. The `msgid` returned by `msgget()` is an identifier for the message queue. We can then use system calls like `msgsnd()` to send a message and `msgrcv()` to receive a message.

Semaphore Queues

Semaphore queues are used for synchronization between processes running on the same machine. A semaphore is a value-based data structure used to help in coordination between processes. The values can be either positive or negative, and they dictate the behavior of the process. Semaphores are managed by the kernel, and they can be accessed by several processes simultaneously.

To create a semaphore, we can use the `semget()` system call as follows:

#include 
#include 
#include 
key_t key = ftok("mypath", 'a');
int semid = semget(key, 1, 0666 | IPC_CREAT);

In the example above, we use `ftok()` to generate a unique key for the semaphore. `semget()` is then used to create a new semaphore with the specified key using the `IPC_CREAT` flag. We can use the `semop()` system call to wait for a semaphore or signal a semaphore.

Shared Memory Queues

Shared memory queues are used for interprocess communication between two or more processes running on a machine. Shared memory is a segment of memory that can be shared between multiple processes. It is a fast and efficient mechanism for interprocess communication as it avoids the overhead of copying data between processes.

To create a shared memory segment, we can use the `shmget()` system call as follows:

#include 
#include 
#include 
key_t key = ftok("mypath", 'a');
int shmid = shmget(key, 1024, 0666 | IPC_CREAT);

In the example above, `shmget()` is used to create a shared memory segment with a size of 1024 bytes. The `shmid` returned is an identifier for the shared memory segment. We can then use the `shmat()` system call to attach the shared memory segment to the calling process’s address space.

Conclusion

In conclusion, Linux queues are a powerful mechanism for interprocess communication and synchronization. In this guide, we explored three types of queues: message queues, semaphore queues, and shared memory queues. We learned how to create and use each of these queues with code examples. The knowledge gained will help beginners understand the use of queues on Linux and how to leverage them to build powerful applications.