What does shared memory mean in php

In PHP, shared memory is an effective way to share and transfer data between two running processes on the same machine. This method allows two unrelated processes to access the same logical memory. Different processes share the same physical memory.

The operating environment of this tutorial: windows10 system, PHP7.1 version, DELL G3 computer

What does shared memory mean in php

Shared memory is an effective way to share and transfer data between two running processes in the same machine. The memory shared between different processes is usually arranged as the same segment of physical memory;

As the name suggests , shared memory allows two unrelated processes to access the same logical memory.

A process can create a memory segment that can be accessed by other processes, as long as it is assigned the correct permissions. Each memory segment has a unique ID (called a shmid) that points to an area of ​​physical memory where other processes can operate on it. Once created and provided with the appropriate permissions, other processes on the same machine can operate on these memory segments: read, write, and delete. If a process writes data to shared memory, the changes will be immediately affected. Any other process can access the same segment of shared memory.

This means that applications written in C can share information with applications written in other languages, such as Java or PHP. Shared memory is widely used in implementations for most languages, so access should not be an issue. To understand the information, we can use a standard format such as XML or JSON.

The use of shared memory is a fast way to exchange data between processes, mainly because the data is passed after the memory segment is created, without involving the kernel. This method is often called inter-process communication (IPC). Other IPC methods include pipes, message queues, RPC, and sockets. This ability to quickly and reliably exchange data between applications is useful when working with an ecosystem of applications that need to communicate with each other. Depending on the size of the ecosystem, the common method of using a database to exchange information between applications can often result in slow queries or even I/O blocking. With shared memory, there is no I/O to slow down developer progress.

Shared memory does not provide a synchronization mechanism. That is to say, there is no automatic mechanism to prevent the second process from starting to read it before the first process finishes writing to the shared memory. So we usually need to use other mechanisms to synchronize access to shared memory.

The proposal of this article is very simple, learn how to use PHP to create and manipulate shared memory segments and use them to store data sets that can be used by other applications. Even if there are no plans to use shared memory to exchange data, it has many benefits in itself because it enables applications to stay away from I/O problems. Storing datasets directly in memory has many advantages, from web service data caching to session sharing. It is a very useful concept that every PHP developer should know.

Advantages and disadvantages of using shared memory

1. Advantages: We can see that using shared memory for inter-process communication is really very convenient, and the function interface It is also simple. The sharing of data also eliminates the need to transfer data between processes, but directly accesses the memory, which also speeds up the efficiency of the program. At the same time, it does not require a certain parent-child relationship between communicating processes like anonymous pipes.

2. Disadvantages: Shared memory does not provide a synchronization mechanism, which makes us often need to use other means to perform inter-process synchronization when using shared memory for inter-process communication.

We can use shared memory as a unique storage option that provides advantages such as fast read/write operations and process interoperability. For web applications, this means:

Cache storage (database queries, web service data, external data)

Session storage

Data exchange between applications

This storage technology is useful not only for caching, but also for exchanging data between applications, as long as the data is stored in a format readable by both ends. Don't underestimate the power of shared memory in web applications. There are many different ways to cleverly implement this storage, the only limit is the creativity and skill of the developer.

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