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Optimize creation of empty arrays in json_decode

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Use the shared empty array from ZVAL_EMPTY_ARRAY

For code that created an 10 arrays of 100000 empty arrays
(has the same result with `$assoc=true` and `{}`)

- This is the worst-case comparison, but I'd expect 0-length arrays to be fairly
  common in regular data for json_decode
- The parser implementation was using function pointers so that third party
  extension developers could reuse the json parser for their own
  data structures, etc. (I think).

  This PR is meant to let those third party extensions continue working
  without changes.

Before this patch: In 0.126 seconds: added 97.99 MiB
After this patch:  In 0.096 seconds: added 41.99 MiB

```php
<?php
$json = '[' . str_repeat('[],', 100000) . "null]";
$start_memory = memory_get_usage();
$start_time = microtime(true);
$result = [];
for ($i = 0; $i < 10; $i++) {
    $result[] = json_decode($json);
}
$end_memory = memory_get_usage();
$end_time = microtime(true);
// Before this patch: In 0.126 seconds: added 97.99 MiB
// After this patch:  In 0.096 seconds: added 41.99 MiB
printf("In %.3f seconds: added %.2f MiB\n", $end_time - $start_time, ($end_memory - $start_memory)/1000000);

// For objects
$json = '[' . str_repeat('{},', 100000) . "null]";
$start_memory = memory_get_usage();
$start_time = microtime(true);
for ($i = 0; $i < 10; $i++) {
    $result[] = json_decode($json, true);
}
$end_memory = memory_get_usage();
$end_time = microtime(true);
// Before this patch: In 0.126 seconds: added 97.99 MiB
// After this patch:  In 0.096 seconds: added 41.99 MiB
printf("In %.3f seconds: added %.2f MiB (objects decoded as arrays) \n", $end_time - $start_time, ($end_memory - $start_memory)/1000000);
```

Closes GH-4861.
This commit is contained in:
Tyson Andre 2019-10-25 19:57:39 -04:00 • committed by Nikita Popov
parent 7816275244
commit 447f07cd28
1 changed files with 12 additions and 2 deletions
Download patch file Download diff file Expand all files Collapse all files

14
ext/json/json_parser.y
View file

@ -76,6 +76,8 @@ int json_yydebug = 1;
%code {
static int php_json_yylex(union YYSTYPE *value, php_json_parser *parser);
static void php_json_yyerror(php_json_parser *parser, char const *msg);
static int php_json_parser_array_create(php_json_parser *parser, zval *array);
static int php_json_parser_object_create(php_json_parser *parser, zval *array);
}
@ -120,7 +122,11 @@ object_end:
members:
/* empty */
{
parser->methods.object_create(parser, &$$);
if ((parser->scanner.options & PHP_JSON_OBJECT_AS_ARRAY) && parser->methods.object_create == php_json_parser_object_create) {
ZVAL_EMPTY_ARRAY(&$$);
} else {
parser->methods.object_create(parser, &$$);
}
}
| member
;
@ -180,7 +186,11 @@ array_end:
elements:
/* empty */
{
parser->methods.array_create(parser, &$$);
if (parser->methods.array_create == php_json_parser_array_create) {
ZVAL_EMPTY_ARRAY(&$$);
} else {
parser->methods.array_create(parser, &$$);
}
}
| element
;