libaio简介
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liaio介绍 linux kernel 提供了5个系统调用来实现异步IO。文中最后介绍的是包装了这些系统调用的用户空间的函数。 libaio系统调用 AIO 系统调用总共五个，后面会一一介绍。* int io_setup ( unsigned nr_events , aio_context_t * ctxp ); * int io_destroy ( aio_context_t ctx ); * int io_submit ( aio_context_t ctx , long nr , struct iocb * cbp []); * int io_cancel ( aio_context_t ctx , struct iocb *, struct io_event * result ); * int io_getevents ( aio_context_t ctx , long min_nr , long nr , struct io_event *events, struct timespec *timeout);
1.异步IO上下文 aio_context_t
>> aio_context_t.c >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
#define
_GNU_SOURCE
/* syscall() is not POSIX */
#include
<stdio.h>
/* for perror() */
#include
<unistd.h>
/* for syscall() */
#include
<sys/syscall.h>
/* for __NR_* definitions */
#include
<linux/aio_abi.h>
/* for AIO types and constants */
inline
int
io_setup
(
unsigned
nr
,
aio_context_t
*
ctxp
)
return
syscall
(
__NR_io_setup
,
nr
,
ctxp
);
inline
int
io_destroy
(
aio_context_t
ctx
)
return
syscall
(
__NR_io_destroy
,
ctx
);
int
main
()
aio_context_t
ctx
;
int
ret
;
ctx
=
0
;
ret
=
io_setup
(
128
,
&
ctx
);
if
(
ret
<
0
)
perror
(
"io_setup error"
);
return
-
1
;
printf
(
"after io_setup ctx:%Ld\\n"
,
ctx
);
ret
=
io_destroy
(
ctx
);
if
(
ret
<
0
)
perror
(
"io_destroy error"
);
return
-
1
;
printf
(
"after io_destroy ctx:%Ld\\n"
,
ctx
);
return
0
;
系统调用io_setup会创建一个所谓的"AIO上下文"(即aio_context，后文也叫‘
AIO context’等)
结构体到在内核中。
aio_context是用以内核实现异步AIO的数据结构。它其实是一个无符号整形,位于头文件
/usr/include/linux/aio_abi.h
。
每个进程都可以有多个 aio_context_t。传入io_setup的第一个参数在这里是128，表示同时驻留在上下文中的IO请求的个数；第二个参数是一个指针，内核会填充这个值。 io_destroy的作用是销毁这个上下文 aio_context_t 上面的例子很简单，创建一个 aio_context_t并销毁。 编译运行,编译时需要连接库libaio（-laio）：typedef unsigned long aio_context_t;
$ gcc
-
Wall
aio_context_t
.
c
-
o
aio_context_t
-
laio
$
./
aio_context_t
after io_setup ctx
:
139730712117248
after
io_destroy ctx
:
139730712117248
2.提交并查询IO
#define _GNU_SOURCE /* syscall() is not POSIX */
#include
<stdio.h>
/* for perror() */
#include
<unistd.h>
/* for syscall() */
#include
<sys/syscall.h>
/* for __NR_* definitions */
#include
<linux/aio_abi.h>
/* for AIO types and constants */
#include
<fcntl.h>
/* O_RDWR */
#include
<string.h>
/* memset() */
#include
<inttypes.h>
/* uint64_t */
inline
int
io_setup
(
unsigned
nr
,
aio_context_t
*
ctxp
)
return
syscall
(
__NR_io_setup
,
nr
,
ctxp
);
inline
int
io_destroy
(
aio_context_t
ctx
)
return
syscall
(
__NR_io_destroy
,
ctx
);
inline
int
io_submit
(
aio_context_t
ctx
,
long
nr
,
struct
iocb
**
iocbpp
)
return
syscall
(
__NR_io_submit
,
ctx
,
nr
,
iocbpp
);
inline
int
io_getevents
(
aio_context_t
ctx
,
long
min_nr
,
long
max_nr
,
struct
io_event
*
events
,
struct
timespec
*
timeout
)
return
syscall
(
__NR_io_getevents
,
ctx
,
min_nr
,
max_nr
,
events
,
timeout
);
int
main
()
aio_context_t
ctx
;
struct
iocb cb
;
struct
iocb
*
cbs
[
1
];
char
data
[
4096
];
struct
io_event events
[
1
];
int
ret
;
int
fd
;
int
i
;
for
(
i
=
0
;
i
<
4096
;
i
++)
data
[
i
]=
i
%
50
+
60
;
fd
=
open
(
"./testfile"
,
O_RDWR
|
O_CREAT
,
S_IRWXU
);
if
(
fd
<
0
)
perror
(
"open error"
);
return
-
1
;
ctx
=
0
;
ret
=
io_setup
(
128
,
&
ctx
);
printf
(
"after io_setup ctx:%ld"
,
ctx
);
if
(
ret
<
0
)
perror
(
"io_setup error"
);
return
-
1
;
/* setup I/O control block */
memset
(&
cb
,
0
,
sizeof
(
cb
));
cb
.
aio_fildes
=
fd
;
cb
.
aio_lio_opcode
=
IOCB_CMD_PWRITE
;
/* command-specific options */
cb
.
aio_buf
=
(
uint64_t
)
data
;
cb
.
aio_offset
=
0
;
cb
.
aio_nbytes
=
4096
;
cbs
[
0
]
=
&
cb
;
ret
=
io_submit
(
ctx
,
1
,
cbs
);
if
(
ret
!=
1
)
if
(
ret
<
0
)
perror
(
"io_submit error"
);
else
fprintf
(
stderr
,
"could not sumbit ios"
);
return
-
1
;
/* get the reply */
ret
=
io_getevents
(
ctx
,
1
,
1
,
events
,
NULL
);
printf
(
"%d\\n"
,
ret
);
struct
iocb
*
result
=
(
struct
iocb
*)
events
[
0
].
obj
;
printf
(
"reusult:%Ld"
,
result
->
aio_buf
);
ret
=
io_destroy
(
ctx
);
if
(
ret
<
0
)
perror
(
"io_destroy error"
);
Mysql出现问题：mysqld: error while loading shared libraries: libaio.so.1: cannot open shared object解决方案
error while loading shared libraries: libaio.so.1
Mysql开发实践：error while loading shared libraries: libaio解决方案