About static variables and concurrency

I suddenly thought of a question today, which is about static variables, and my previous manager also said that the static keyword should be used as little as possible in the program.
This is how I understand it now, because I have seen the concept of concurrency before. You see, static is commonly said to be owned by all objects. Doesn’t that mean that in a concurrent situation, multiple users will jointly own some variables, such as purchasing goods? The quantity is set to static. In this way, it is impossible to distinguish which user purchased how many goods. I think this example is not very good, but the general meaning is this. All objects are owned together, so there is no need to distinguish which object? Is there any hero who can answer my questions or provide a practical application scenario? Thanks again

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I suddenly thought of a question today, which is about static variables, and my previous manager also said that the static keyword should be used as little as possible in the program.
This is how I understand it now, because I have seen the concept of concurrency before. You see, static is commonly said to be owned by all objects. Doesn’t that mean that in a concurrent situation, multiple users will jointly own some variables, such as purchasing goods? The quantity is set to static. In this way, it is impossible to distinguish which user purchased how many goods. I think this example is not very good, but the general meaning is this. All objects are owned together, so there is no need to distinguish which object? Is there anyone who can answer my questions, or give me a practical application scenario? Thanks again

I think there is something wrong with your understanding:
First of all: for each http request, for example, through nginx reverse proxy to fastcgi server, different requests are parsed and executed in different php-fpm processes, and each process (system performs The basic unit of resource allocation and scheduling) is exclusive memory without interfering with each other;
Secondly: static static attributes are directly loaded into the memory (heap) when the script is executed (in theory, it is better than creating an object and then calling the attributes) High efficiency);
So: this static has nothing to do with concurrency, but proper use of the static attribute will theoretically increase the execution speed of the script, so it will reduce the execution time of the script unit, thereby improving the performance of the system during concurrency. Stress resistance.

Extra: The number of concurrency of php theoretically depends on the number of processes of php-fpm

static is held by the class, not by the object. At this time, the class has not been instantiated, and there are no objects, let alone all objects.

static variable is a class attribute, which means that all objects of this class are shared. For example, it is the number of train tickets for a certain train. Users from all over the country can buy train tickets for this train, but how to determine the remaining number of the train tickets? What about the number of votes? One of the implementations can be achieved through static variables. Define the remaining number of train tickets as static. Every time someone purchases a ticket (different object), the attribute is modified synchronously (static - 1)
You can check the meaning of the static keyword

Let me say some unkind words.
What is the answer you adopted saying? I think you should use your own judgment before accepting the answer.
Or read the document first before doing this.

The correct statement @TIGERB has made it very clear.

Each HTTP request will be in exclusive memory

static actually has nothing to do with concurrency. To quote TIGERB again

But proper use of static attributes will theoretically improve script execution speed

It’s also obvious that you don’t need to think too much about this theoretical improvement.
Concurrency you should consider more
1 Network IO (http request, TCP, IP handshake time).
2 Database IO, concurrent reading and writing are blocked. Use correct and appropriate indexes for large amounts of data, and separate reading and writing.
3 Use caching.
4 Wait.
These have nothing to do with this staic.

Just answer your last question:

Or give a practical application scenario

Before this, I think the subject should understand the difference between static, $this, and self in PHP.

For example, static can be used in the design pattern - static factory pattern. For specific design patterns, the subject can refer to other people’s articles.

Finally let’s talk about the difference:

<code>class A {
    public static function get_self() {
        return new self();
    }

    public static function get_static() {
        return new static();
    }
}

class B extends A {}

echo get_class(B::get_self());  // A
echo get_class(B::get_static()); // B
echo get_class(A::get_self()); // A
echo get_class(A::get_static()); // A</code>