Detailed explanation of destructor and PHP's garbage collection mechanism_PHP tutorial

Destructor: Executed when an object becomes garbage or when the object is explicitly destroyed.

GC(Garbage Collector)

In PHP, when no variable points to this object, the object becomes garbage. PHP will destroy it in memory.

This is PHP's GC (Garbage Collector) garbage disposal mechanism to prevent memory overflow.

When a PHP thread ends, all memory space currently occupied will be destroyed, and all objects in the current program will also be destroyed.

__destruct() destructor

__destruct() The destructor is executed when the garbage object is recycled.

The destructor can also be called explicitly, but don't do it.

The destructor is automatically called by the system. Do not call fictitious functions of an object in the program.

Destructor cannot take parameters.

As shown in the program below, all objects are destroyed before the program ends. The destructor is called.

Copy code The code is as follows:

class Person {
public function __destruct(){
Echo 'Development function is now executed & lt; br /& gt;';
Echo 'Here is generally used to set up, close database, close files, etc. >
$p = new Person();
for($i = 0; $i echo "$i
";
}

?>


Program execution result:
0

1
2
3
4

The destructor is now executed
This is generally used for finishing work such as setting up, closing the database, closing files, etc.

When the object is not pointed to, the object is destroyed.



Copy code

The code is as follows:

class Person {

public function __destruct(){
Echo 'Discirate function is now executed & lt; br /& gt;';
}
}

$ p = new person ();
$ p = null; / / / / / The destructor is executed here
$p = "abc"; // The same effect
for($i = 0; $i echo "$i
";
}

?>


Program execution result:

The destructor is now executed
0 1

2
3
4

In line 10 of the above example, we set $p to empty or Line 11 assigns $p a string, so that the object pointed to by $p becomes a garbage object. PHP trashes this object.
php unset variable



Copy code

The code is as follows:

class Person {
public function __destruct(){
echo 'The destructor is now executed
';
}
}

$p = new Person();
$p1 = $p;

unset($p);
echo 'Now that $p is destroyed, is the object also destroyed?
';

for($i = 0; $i echo "$i
";
}

echo 'Now destroy $p1, that is, there is no variable pointing to the object
';
unset($p1); // Now there is no variable pointing to the object Yes, the destructor is executed here

?>


Program execution result:

Now that $p is destroyed, is the object also destroyed?
0 1

2
3
4

Now destroy $p1, that is, there is no variable pointing to the object

The destructor is now executed.

unset destroys the variable pointing to the object, not the object.

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