valgrind 报告 ecpg内存泄露 (三)-优快云博客

本文深入探讨了使用ecpg时遇到的内存泄露问题，通过GDB调试发现并解释了全局变量sqlca的内存管理不当，以及如何在特定函数中正确释放内存以避免泄露。

摘要生成于 C知道，由 DeepSeek-R1 满血版支持，前往体验 >

valgrind为何报 ecpg内存泄露错误？根据我的同事的研究成果：

究其原因，全局变量 sqlca 由malloc形成,但是释放时是隐含的：

ecpg_sqlca_key_destructor函数调用 free 进行释放。

bool
ECPGconnect(int lineno, int c, const char *name, const char *user, const char *passwd, const char *connection_name, int autocommit){
struct sqlca_t *sqlca = ECPGget_sqlca();
        ．．．．．．
struct sqlca_t *
ECPGget_sqlca(void)
{
#ifdef ENABLE_THREAD_SAFETY
        struct sqlca_t *sqlca;
        pthread_once(&sqlca_key_once, ecpg_sqlca_key_init);
        sqlca = pthread_getspecific(sqlca_key);
        if (sqlca == NULL){
                sqlca = malloc(sizeof(struct sqlca_t));
                ecpg_init_sqlca(sqlca);
                pthread_setspecific(sqlca_key, sqlca);
        }
        return (sqlca);
#else
        return (&sqlca);
#endif
} 
static void
ecpg_sqlca_key_init(void){
        pthread_key_create(&sqlca_key, ecpg_sqlca_key_destructor);
}
 
static void
ecpg_sqlca_key_destructor(void *arg){
        free(arg);        /* sqlca structure allocated in ECPGget_sqlca */
}

用GDB来调试，也可以验证这一点：

GNU gdb (GDB) Red Hat Enterprise Linux (7.2-50.el6)
Copyright (C) 2010 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.  Type "show copying"
and "show warranty" for details.
This GDB was configured as "i686-redhat-linux-gnu".
For bug reporting instructions, please see:
<http://www.gnu.org/software/gdb/bugs/>.

(gdb) file memoryleak
Reading symbols from /usr/local/pgsql/bin/memoryleak...done.
(gdb) break main
Breakpoint 1 at 0x804875e: file memoryleak.pgc, line 51.
(gdb) run
Starting program: /usr/local/pgsql/bin/memoryleak
[Thread debugging using libthread_db enabled]
 
Breakpoint 1, main (argc=1, argv=0xbffff6f4) at memoryleak.pgc:51
51        PerformTask( 25 );
Missing separate debuginfos, use: debuginfo-install glibc-2.12-1.80.el6.i686
(gdb) delete
Delete all breakpoints? (y or n) y
(gdb) break ecpg_sqlca_key_destructor
Breakpoint 2 at 0x1af9b2: file misc.c, line 124.
(gdb) list misc.c:124
119
120     #ifdef ENABLE_THREAD_SAFETY
121     static void
122     ecpg_sqlca_key_destructor(void *arg)
123     {
124             free(arg);                                      /* sqlca structure allocated in ECPGget_sqlca */
125     }
126
127     static void
128     ecpg_sqlca_key_init(void)
(gdb) break misc.c:147
Breakpoint 3 at 0x1afa4e: file misc.c, line 147.
(gdb) list misc.c:134,misc.c:149
134     struct sqlca_t *
135     ECPGget_sqlca(void)
136     {
137     #ifdef ENABLE_THREAD_SAFETY
138             struct sqlca_t *sqlca;
139
140             pthread_once(&sqlca_key_once, ecpg_sqlca_key_init);
141
142             sqlca = pthread_getspecific(sqlca_key);
143             if (sqlca == NULL)
144             {
145                     sqlca = malloc(sizeof(struct sqlca_t));
146                     ecpg_init_sqlca(sqlca);
147                     pthread_setspecific(sqlca_key, sqlca);
148             }
149             return (sqlca);
(gdb) cont
Continuing.
[New Thread 0xb7ff0b70 (LWP 2936)]
[Switching to Thread 0xb7ff0b70 (LWP 2936)]
Breakpoint 3, ECPGget_sqlca () at misc.c:147
147                     pthread_setspecific(sqlca_key, sqlca);
(gdb) where
#0  ECPGget_sqlca () at misc.c:147
#1  0x001aed62 in ECPGconnect (lineno=29, c=0, name=0xb7400468 "postgres@192.168.66.123:5432", user=0x804884b "postgres", passwd=0x804884b "postgres",
    connection_name=0x8048844 "dbConn", autocommit=0) at connect.c:268
#2  0x080486bf in Work () at memoryleak.pgc:29
#3  0x00117a49 in start_thread () from /lib/libpthread.so.0
#4  0x00353e1e in clone () from /lib/libc.so.6
(gdb) print sqlca
$1 = (struct sqlca_t *) 0xb7400490
(gdb) cont
Continuing.
conncet ok
Breakpoint 2, ecpg_sqlca_key_destructor (arg=0xb7400490) at misc.c:124
124             free(arg);                                      /* sqlca structure allocated in ECPGget_sqlca */
Missing separate debuginfos, use: debuginfo-install libgcc-4.4.6-4.el6.i686
(gdb) print arg
$2 = (void *) 0xb7400490
(gdb) cont
Continuing.
[Thread 0xb7ff0b70 (LWP 2936) exited] 
Program exited normally.
(gdb)