php high-performance writing_PHP tutorial-PHP Tutorial-php.cn

php high-performance writing_PHP tutorial

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Release： 2016-07-21 15:33:33

Original

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It has been 4 years since I switched from .NET to PHP, and recently I started to pursue high performance~~
So I started to think it’s time to write a blog~
Let’s discover something first~

Copy code The code is as follows:

 
$arr = array( 
'attr1' => 1 , 
'attr2' => 1 , 
'attr3' => 1 , 
); 
$startTime = microtime( true ); 
for( $i = 0 ; $i < 1000 ; $i++ ) 
{ 
if( isset( $arr['attr1'] ) ) 
{ 

} 
if( isset( $arr['attr2'] ) ) 
{ 
 
} 
if( isset( $arr['attr3'] ) ) 
{ 

} 
} 
$endTime = microtime( true ); 
printf ( "%d us.n" , ( $endTime - $startTime ) * 1000000 ); 
$startTime = microtime( true ); 
for( $i = 0 ; $i < 1000 ; $i++ ) 
{ 
foreach( $arr as $key => $value ) 
{ 
switch( $key ) 
{ 
case 'attr1': 
break; 
case 'attr2': 
break; 
case 'attr3': 
break; 
} 
} 
} 
$endTime = microtime( true ); 
printf( "%d us.n" , ( $endTime - $startTime ) * 1000000 ); 

The output result of the above code
is
us.
us.
However, no matter how you look at it, the first paragraph is more cumbersome than the second paragraph, and the structure is not as clear as the second paragraph.
So why does the first paragraph execute so much faster than the second paragraph?
We can Seeing that there are only 3 ifs in the first paragraph of code,
then how many will there be in the second paragraph.
We have disassembled the switch and can take a look at its basic implementation principles.
If each case in the switch ends with break;,
In fact, this switch is like multiple if{}else if{}

So from this mechanism, we can The

copy code The code is as follows:

 
foreach( $arr as $key => $value ) 
{ 
switch( $key ) 
{ 
case 'attr1': 
break; 
case 'attr2': 
break; 
case 'attr3': 
break ; 
} 
} 

is converted into

Copy code The code is as follows:

 
foreach( $arr as $key => $value ) 
{ 
if( $key == 'attr1' ) 
{ 

} 
else if( $ key == 'attr2' ) 
{ 

} 
else if( $key == 'attr3' ) 
{ 

} 
} 
 

To understand,
From here you can see that the second piece of code will continuously make judgments of 1+2+3 according to the number of keys in the array. , so the number of judgments for the first piece of code is 3, and the number of judgments for the second piece of code is 6 times

, so the execution efficiency is nearly doubled.