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This article mainly explains "what is a PHP file lock". The content of the article is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought to study and learn "what is a PHP file lock".

What is a file lock?

First of all, a file lock is simply a file protection mechanism, which can be understood to mean that when you are reading or writing to the file, that is, when one is already operating on the file, a protection mechanism for the file, as an example, to avoid being manipulated by another during the operation of the file.

The purpose of the file lock

If a file has a file lock, only I can operate on the file when I am using the file, and no one else can interfere with my operation on the file unless the file lock is released. Only one person can be allowed to operate at the same time to prevent data errors.

If there is no file lock, there are multiple people operating the same file, which is very likely to cause data errors or asymmetry, so it is necessary to use file locks. This is what files are used for and why file locks are used.

How to use file locks: the flock () function

Let's take a look at how to use the PHP file lock. First we need to know that we can lock the file through the flock () function after opening the file.

The basic syntax format of the flock () function is as follows:

Flock (resource $handle, int $operation [, int & $wouldblock])

Among them, it should be noted that:

The parameter $handle represents the pointer to the file system, that is, the file resource created by fopen (); the parameter $operation represents the file lock type; and the parameter $wouldblock is an optional parameter, which means that it can be set to 1 or true, so that other processes will be blocked when the file is locked.

Let's introduce the type of parameter $operation:

LOCK_EX represents a write lock, that is, it is in a write lock state at the time of writing, and others cannot write or read, and can only be restored after it is unlocked.

LOCK_SH means shared lock, which is understood to mean that others can only read but cannot write. Reply when unlocked.

LOCK_UN means to release the above two states. That is, unlock it.

LOCK_NB means that after reading or writing, when the file is locked, it will immediately return to notify that the accessed file is locked.

Next, let's take a look at the example, which is as follows:

Output result:

Data is written in the test.txt:

From the above example, we have finished locking the file, using the fclose () function to close the file, and then reading the file contents through the readfile () function. Among them, it should be noted that:

When we use the flock () function, we lock the file. To unlock the file automatically, we just need to call the fclose () function. It is better to add an unlock statement after using the file lock when we write the code.

Thank you for your reading, the above is the content of "what is a PHP file lock", after the study of this article, I believe you have a deeper understanding of what is a PHP file lock, and the specific use needs to be verified in practice. Here is, the editor will push for you more related knowledge points of the article, welcome to follow!

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