最近在帮同事解决Swoole Server问题时，发现有1个worker进程一直处于R的状态，而且cpu耗时非常高。初步断定是PHP代码中发生死循环。
PHP
$array = array();
for($i = 0; $i < 10000; $i++)
{
$array[] = $i;
}
include __DIR__."/include.PHP";
#include.PHP
while(1)
{
usleep(10);
$keys = array_flip($array);
$index = array_search(rand(1500,9999),$array);
$str = str_repeat('A',$index);
$strb = test($index,$str);
}
function test($index,$str)
{
return str_replace('A','B',$str);
}
通过ps aux得到进程ID和状态如下，使用gdb -p 进程ptrace跟踪，通过bt命令得到调用栈
代码如下:
PHP dead_loop.PHP
gdb -p 3834
(gdb) bt
#0 0x00000000008cc03f in zend_mm_check_ptr (heap=0x1eaa2c0,ptr=0x2584910,silent=1,__zend_filename=0xee3d40 "/home/htf/workspace/PHP-5.4.27/Zend/zend_variables.c",
__zend_lineno=182,__zend_orig_filename=0xee1888 "/home/htf/workspace/PHP-5.4.27/Zend/zend_execute_API.c",__zend_orig_lineno=437)
at /home/htf/workspace/PHP-5.4.27/Zend/zend_alloc.c:1485
#1 0x00000000008cd643 in _zend_mm_free_int (heap=0x1eaa2c0,p=0x2584910,__zend_lineno=182,
__zend_orig_filename=0xee1888 "/home/htf/workspace/PHP-5.4.27/Zend/zend_execute_API.c",__zend_orig_lineno=437) at /home/htf/workspace/PHP-5.4.27/Zend/zend_alloc.c:2064
#2 0x00000000008cebf7 in _efree (ptr=0x2584910,__zend_orig_lineno=437) at /home/htf/workspace/PHP-5.4.27/Zend/zend_alloc.c:2436
#3 0x00000000008eda0a in _zval_ptr_dtor (zval_ptr=0x25849a0,__zend_lineno=182)
at /home/htf/workspace/PHP-5.4.27/Zend/zend_execute_API.c:437
#4 0x00000000008fe687 in _zval_ptr_dtor_wrapper (zval_ptr=0x25849a0) at /home/htf/workspace/PHP-5.4.27/Zend/zend_variables.c:182
#5 0x000000000091259f in zend_hash_destroy (ht=0x7f7263f6e380) at /home/htf/workspace/PHP-5.4.27/Zend/zend_hash.c:560
#6 0x00000000008fe2c5 in _zval_dtor_func (zvalue=0x7f726426fe50,__zend_filename=0xeea290 "/home/htf/workspace/PHP-5.4.27/Zend/zend_execute.c",__zend_lineno=901)
at /home/htf/workspace/PHP-5.4.27/Zend/zend_variables.c:45
#7 0x0000000000936656 in _zval_dtor (zvalue=0x7f726426fe50,__zend_lineno=901)
at /home/htf/workspace/PHP-5.4.27/Zend/zend_variables.h:35
#8 0x0000000000939747 in zend_assign_to_variable (variable_ptr_ptr=0x7f7263f8e738,value=0x7f726426f6a8) at /home/htf/workspace/PHP-5.4.27/Zend/zend_execute.c:901
#9 0x0000000000997ee5 in ZEND_ASSIGN_SPEC_CV_VAR_HANDLER (execute_data=0x7f726d04b2a8) at /home/htf/workspace/PHP-5.4.27/Zend/zend_vm_execute.h:33168
#10 0x000000000093b5fd in execute (op_array=0x21d58b0) at /home/htf/workspace/PHP-5.4.27/Zend/zend_vm_execute.h:410
#11 0x0000000000901692 in zend_execute_scripts (type=8,retval=0x0,file_count=3) at /home/htf/workspace/PHP-5.4.27/Zend/zend.c:1315
#12 0x000000000087926a in PHP_execute_script (primary_file=0x7ffffe0038d0) at /home/htf/workspace/PHP-5.4.27/main/main.c:2502
#13 0x00000000009a32e3 in do_cli (argc=2,argv=0x7ffffe004d18) at /home/htf/workspace/PHP-5.4.27/sapi/cli/PHP_cli.c:989
#14 0x00000000009a4491 in main (argc=2,argv=0x7ffffe004d18) at /home/htf/workspace/PHP-5.4.27/sapi/cli/PHP_cli.c:1365
执行gdb后，死循环的进程会变成T的状态，表示正在Trace。这个是独占的，所以不能再使用strace/gdb或者其他ptrace工具对此进程进行调试。另外此进程会中断执行。gdb输入c后，程序继续向下运行。然后再次按下ctrl + c中断程序。 通过bt命令查看进程的调用栈。
代码如下:
PHP-5.4.27/ext/standard/array.c",__zend_lineno=2719,
__zend_orig_filename=0xee5a38 "/home/htf/workspace/PHP-5.4.27/Zend/zend_hash.c",__zend_orig_lineno=412) at /home/htf/workspace/PHP-5.4.27/Zend/zend_alloc.c:1895
#1 0x00000000008ceb86 in _emalloc (size=72,__zend_orig_lineno=412) at /home/htf/workspace/PHP-5.4.27/Zend/zend_alloc.c:2425
#2 0x0000000000911d85 in _zend_hash_index_update_or_next_insert (ht=0x2257a10,h=3972,pData=0x7ffffe0012b0,nDataSize=8,pDest=0x0,flag=1,
__zend_filename=0xe43410 "/home/htf/workspace/PHP-5.4.27/ext/standard/array.c",__zend_lineno=2719) at /home/htf/workspace/PHP-5.4.27/Zend/zend_hash.c:412
#3 0x00000000007767e1 in zif_array_flip (ht=1,return_value=0x7f726424ea68,return_value_ptr=0x0,this_ptr=0x0,return_value_used=1)
at /home/htf/workspace/PHP-5.4.27/ext/standard/array.c:2719
#4 0x000000000093c03e in zend_do_fcall_common_helper_SPEC (execute_data=0x7f726d04b2a8) at /home/htf/workspace/PHP-5.4.27/Zend/zend_vm_execute.h:643
#5 0x00000000009400e6 in ZEND_DO_FCALL_SPEC_CONST_HANDLER (execute_data=0x7f726d04b2a8) at /home/htf/workspace/PHP-5.4.27/Zend/zend_vm_execute.h:2233
#6 0x000000000093b5fd in execute (op_array=0x21d58b0) at /home/htf/workspace/PHP-5.4.27/Zend/zend_vm_execute.h:410
两次的BT信息不一样，这是因为程序在不同的位置中断。看到execute (oparray=0x21d58b0) 这一行，这里就是PHP执行oparray的入口了。gdb下输入f 6，(通过调用栈编号可得)。
代码如下:
handler(execute_data TSRMLS_CC)) > 0) {
(gdb) p *op_array
$2 = {type = 2 '\002',function_name = 0x7f726d086540 "test",scope = 0x0,fn_flags = 134217728,prototype = 0x0,num_args = 2,required_num_args = 2,arg_info = 0x7f726d086bd8,
refcount = 0x7f726d0870f0,opcodes = 0x7f726424d600,last = 8,vars = 0x7f726424e890,last_var = 2,T = 1,brk_cont_array = 0x0,last_brk_cont = 0,try_catch_array = 0x0,
last_try_catch = 0,static_variables = 0x0,this_var = 4294967295,filename = 0x7f726424ba38 "/home/htf/wwwroot/include.PHP",line_start = 12,line_end = 15,doc_comment = 0x0,
doc_comment_len = 0,early_binding = 4294967295,literals = 0x7f726424eae0,last_literal = 4,run_time_cache = 0x7f726450bfb0,last_cache_slot = 1,reserved = {0x0,0x0,0x0}}
这里的filename就能看到op_array是哪个PHP文件的。然后输入f 0进入当前位置。
代码如下:
