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php控制结构语句declare中的tick的详解[整理版]

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リリース: 2016-06-06 19:50:25
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先看看手册是怎么说的: declare 结构用来设定一段代码的执行指令。 declare 的语法和其它流程控制结构相: 1 declare (directive) 2 statement directive 部分允许设定 declare 代码段的行为。目前只认识两个指令: ticks (更多信息见下面ticks指令)以及 e

先看看手册是怎么说的:

declare 结构用来设定一段代码的执行指令。declare 的语法和其它流程控制结构相似:

1 declare (directive)

2     statement

directive 部分允许设定 declare 代码段的行为。目前只认识两个指令:ticks(更多信息见下面 ticks 指令)以及encoding(更多信息见下面 encoding指令)。

Note

ticks 指令在 PHP 5.3.0 中是过时指令,将会从 PHP 6.0.0 移除。

encoding 是 PHP 5.3.0 新增指令。

Tick 是一个在 declare 代码段中解释器每执行 N 条低级语句就会发生的事件。N 的值是在 declare 中的 directive部分用 ticks=N 来指定的。

在每个 tick 中出现的事件是由 register_tick_function() 来指定的。更多细节见下面的例子。注意每个 tick 中可以出现多个事件。

看完手册还是觉得云里雾里,再看看别人是怎么描述:


根据代码解析:

01 <?php

02 function doTicks ()

03 {

04     echo 'Ticks';

05 }

06 register_tick_function('doTicks');

07 declare(ticks = 1) {

08     for (<code>$x = 1; <code>$x <code>$x) {

09         echo <code>$x <code>$x '<br>';

10     }

11 }

12 ?>

运算结果:

01 1

02 TicksTicks4

03 TicksTicks9

04 TicksTicks16

05 TicksTicks25

06 TicksTicks36

07 TicksTicks49

08 TicksTicks64

09 TicksTicks81

10 TicksTicksTicksTicks

产生三个疑问:


(1)为什么先输出1之后才输出“Ticks”? 

(2)为什么在输出81后还输出四个Ticks ? 

(3)declare中的for循环怎么分解成低级语句(low-level)?

这是每个初次接触ticks的人都会碰到的问题。首先register_tick_function函数定义了每个tick事件发生时的处理函数。那么什么是tick事件呢?先看手册上对ticks的解释:

1 A tick is an event that occurs for every N low-level statements executed by the parser within the declare block. The value for N is specified using ticks=N within the declare blocks's directive div.

2 The event(s) that occur on each tick are specified using the register_tick_function().

这个解释有三层意思:

(1) tick是一个事件。

(2) tick事件在PHP每执行N条低级语句就发生一次,N由declare语句指定。

(3)可以用register_tick_function()来指定tick事件发生时应该执行的操作。

很明显,理解上面的输出结果最关键的是了解什么是低级语句(low-level statements),它又是如何进行计数的。我们首先还是将上面的程序通过OPDUMP编译成OPCODEs:

01 1: <?php

02         0  NOP                

03 2:

04 3: function doTicks ()

05 4: {

06 5:     echo 'Ticks';

07         0  ECHO                'Ticks'

08 6: }

09         1  RETURN              null

10 7: register_tick_function('doTicks');

11         1  SEND_VAL            'doTicks'

12         2  DO_FCALL            'register_tick_function' [extval:1]

13 8: declare(ticks = 1) {

14 9:     for (<code>$x = 1; <code>$x <code>$x) {

15         3  ASSIGN              !0, 1

16         4  IS_SMALLER          !0, 10 =>RES[~2]     

17         5  JMPZNZ              ~2, ->14 [extval:8]

18         6  PRE_INC             !0

19         7  JMP                 ->4

20 10:         echo <code>$x <code>$x '<br>';

21         8  MUL                 !0, !0 =>RES[~4]     

22         9  CONCAT              ~4, '<br>' =>RES[~5]     

23        10  ECHO                ~5

24        11  TICKS               1 =>RES[]       

25 11:     }

26        12  TICKS               1 =>RES[]       

27        13  JMP                 ->6

28        14  TICKS               1 =>RES[]       

29 12: }

30        15  TICKS               1 =>RES[]       

31        16  RETURN              1

很明显,PHP的编译过程已经在编译后每条语句的OPCODE序列中插入了TICKS指令用于处理tick事件。那么这些TICKS是根据什么规则来插入的呢?

我们还是从PHP Zend Engine的源代码中寻找答案。

    通过简单的文本搜索我们可以知道生成ZEND_TICKS指令的唯一函数是zend_do_ticks(该函数的实现在zend_compile.c中)。

    现在再从PHP的语法分析文件zend_language_parser.y(PHP使用bison来做语法分析,所有的语法规则均定义在zend_language_parser.y中)中寻找调用zend_do_ticks的地方。

    再一次使用简单的文本搜索,我们可以得到调用zend_do_ticks的三条语法规则:

01 statement:

02   unticked_statement { zend_do_ticks(TSRMLS_C); }

03 | ...

04 ;

05 function_declaration_statement:

06   unticked_function_declaration_statement { zend_do_ticks(TSRMLS_C); }

07 ;

08 class_declaration_statement:

09   unticked_class_declaration_statement { zend_do_ticks(TSRMLS_C); }

10 ;

    也就是说,PHP编译会在statement(语句), function_declaration_statement(函数定义语句), class_declaration_statement后插入TICKS处理函数,即它会在每条statement,函数声明,类(实际上还包括接口)声明后插入一条TICKS指令。

    函数与类声明语句比较好理解,根据unticked_function_declaration_statement的语法定义:

1 unticked_function_declaration_statement:

2   function is_reference T_STRING { zend_do_begin_function_declaration(&$1, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$3, 0, $2.op_type, NULL TSRMLS_CC); }

3    '(' parameter_list ')' '{' inner_statement_list '}' { zend_do_end_function_declaration(&$1TSRMLS_CC); }

4 ;
    可以知道function_declaration_statement是完整的函数声明,也就是说,一个函数的定义包括完整的函数原形及函数体算一条function_declaration_statement。 

    同样从unticked_class_declaration_statement的语法定义:

01 unticked_class_declaration_statement:

02   class_entry_type T_STRING extends_from

03    { zend_do_begin_class_declaration(&amp;$1, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$2, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$3 TSRMLS_CC); }

04    implements_list

05    '{'

06     class_statement_list

07    '}' { zend_do_end_class_declaration(&amp;$1, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$2 TSRMLS_CC); }

08 | interface_entry T_STRING

09    { zend_do_begin_class_declaration(&amp;$1, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$2, NULL TSRMLS_CC); }

10    interface_extends_list

11    '{'

12     class_statement_list

13    '}' { zend_do_end_class_declaration(&amp;$1, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$2 TSRMLS_CC); }

14 ;
    也可以知道,完整的class或interface定义算是一个class_declration_statement。

    最复杂的是statement,它的核心是下面的定义:

01 unticked_statement:

02   '{' inner_statement_list '}'

03 | T_IF '(' expr ')' { zend_do_if_cond(&amp;$3, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$4 TSRMLS_CC); } statement { zend_do_if_after_statement(&$4, 1 TSRMLS_CC); } elseif_list else_single { zend_do_if_end(TSRMLS_C); }

04 | T_IF '(' expr ')' ':' { zend_do_if_cond(&amp;$3, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$4 TSRMLS_CC); } inner_statement_list { zend_do_if_after_statement(&$4, 1 TSRMLS_CC); } new_elseif_list new_else_single T_ENDIF ';' { zend_do_if_end(TSRMLS_C); }

05 | T_WHILE '(' $1.u.opline_num = get_next_op_number(CG(active_op_array));  } expr  ')' { zend_do_while_cond(&$4, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$5 TSRMLS_CC); } while_statement { zend_do_while_end(&$1, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$5TSRMLS_CC); }

06 | T_DO { $1.u.opline_num = get_next_op_number(CG(active_op_array));  zend_do_do_while_begin(TSRMLS_C); } statement T_WHILE '(' $5.u.opline_num = get_next_op_number(CG(active_op_array)); } expr ')' ';' { zend_do_do_while_end(&$1, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$5, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$7TSRMLS_CC); }

07 | T_FOR

08    '('

09     for_expr

10    ';' { zend_do_free(&amp;amp;$3 TSRMLS_CC); $4.u.opline_num = get_next_op_number(CG(active_op_array)); }

11     for_expr

12    ';' { zend_do_extended_info(TSRMLS_C); zend_do_for_cond(&$6, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$7 TSRMLS_CC); }

13     for_expr

14    ')' { zend_do_free(&amp;amp;$9 TSRMLS_CC); zend_do_for_before_statement(&$4, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$7 TSRMLS_CC); }

15    for_statement { zend_do_for_end(&$7 TSRMLS_CC); }

16 | T_SWITCH '(' expr ')' { zend_do_switch_cond(&$3 TSRMLS_CC); } switch_case_list { zend_do_switch_end(&$6 TSRMLS_CC); }

17 | T_BREAK ';'    { zend_do_brk_cont(ZEND_BRK, NULL TSRMLS_CC); }

18 | T_BREAK expr ';'  { zend_do_brk_cont(ZEND_BRK, &$2 TSRMLS_CC); }

19 | T_CONTINUE ';'   { zend_do_brk_cont(ZEND_CONT, NULL TSRMLS_CC); }

20 | T_CONTINUE expr ';'  { zend_do_brk_cont(ZEND_CONT, &$2 TSRMLS_CC); }

21 | T_RETURN ';'      { zend_do_return(NULL, 0 TSRMLS_CC); }

22 | T_RETURN expr_without_variable ';' { zend_do_return(&amp;$2, 0 TSRMLS_CC); }

23 | T_RETURN variable ';'    { zend_do_return(&amp;$2, 1 TSRMLS_CC); }

24 | T_GLOBAL global_var_list ';'

25 | T_STATIC static_var_list ';'

26 | T_ECHO echo_expr_list ';'

27 | T_INLINE_HTML   { zend_do_echo(&$1 TSRMLS_CC); }

28 | expr ';'    { zend_do_free(&amp;amp;$1 TSRMLS_CC); }

29 | T_UNSET '(' unset_variables ')' ';'

30 | T_FOREACH '(' variable T_AS

31   { zend_do_foreach_begin(&amp;$1, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$2, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$3, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$4, 1 TSRMLS_CC); }

32   foreach_variable foreach_optional_arg ')' { zend_do_foreach_cont(&$1, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$2, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$4, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$6, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$7TSRMLS_CC); }

33   foreach_statement { zend_do_foreach_end(&amp;$1, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$4 TSRMLS_CC); }

34 | T_FOREACH '(' expr_without_variable T_AS

35   { zend_do_foreach_begin(&amp;$1, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$2, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$3, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$4, 0 TSRMLS_CC); }

36   variable foreach_optional_arg ')' { zend_check_writable_variable(&$6); zend_do_foreach_cont(&$1, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$2, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$4, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$6, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$7 TSRMLS_CC); }

37   foreach_statement { zend_do_foreach_end(&amp;$1, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$4 TSRMLS_CC); }

38 | T_DECLARE { $1.u.opline_num = get_next_op_number(CG(active_op_array)); zend_do_declare_begin(TSRMLS_C); } '(' declare_list ')' declare_statement { zend_do_declare_end(&$1 TSRMLS_CC); }

39 ';'  /* empty statement */

40 | T_TRY { zend_do_try(&$1 TSRMLS_CC); } '{' inner_statement_list '}'

41   T_CATCH '(' { zend_initialize_try_catch_element(&$1 TSRMLS_CC); }

42   fully_qualified_class_name { zend_do_first_catch(&$7 TSRMLS_CC); }

43   T_VARIABLE ')' { zend_do_begin_catch(&$1, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$9, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$11, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$7 TSRMLS_CC); }

44   '{' inner_statement_list '}' { zend_do_end_catch(&$1 TSRMLS_CC); }

45   additional_catches { zend_do_mark_last_catch(&$7, &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;$18 TSRMLS_CC); }

46 | T_THROW expr ';' { zend_do_throw(&$2 TSRMLS_CC); }

47 | T_GOTO T_STRING ';' { zend_do_goto(&$2 TSRMLS_CC); }

48 ;

根据上面的定义,我们知道,statement包括:

(1) 简单语句:空语句(就一个;号),return,break,continue,throw, goto,global,static,unset,echo, 内置的HTML文本,分号结束的表达式等均算一个语句。

(2) 复合语句:完整的if/elseif,while,do...while,for,foreach,switch,try...catch等算一个语句。

(3) 语句块:{} 括出来的语句块。

(4) 最后特别的:declare块本身也算一个语句(按道理declare块也算是复合语句,但此处特意将其独立出来)。

所有的statement, function_declare_statement, class_declare_statement就构成了所谓的低级语句(low-level statement)。


现在再来看开始的例子就比较好理解了:

首先完整的for循环算一个语句,但必须要等循环结束才算,因此在编译时for循环里面的echo 算第一个语句。

所以第一个doTicks是在第一个echo后执行的,也就是1输出后才发生第一个tick事件。

在$x 从1到9的循环中,每个循环包括两个语句,一个echo, 一个for循环。在81输出后,因为echo是一条语句,因此输出第一个ticks。

同时$x=9的这个for循环也结束了,这又是一条语句,输出第二个ticks;开始$x=10的循环,但这时已不满足循环条件,for循环执行结束,这个循环又是一个语句,这时输出第三个ticks。

最后declare本身也算一条语句,所以又输出第四个ticks。


说了半天,ticks到底有什么用?实际上可用tick来进行调试,性能测试,实现简单的多任务,或者做一些后台的I/O操作等等。

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