我正在寻找POSIX aio_write
功能的简单示例。
以下内容不太重要。只需跳转即可回答
下面的代码创建一个文件,但不向其中写入任何内容。 aio_error返回22
(= quota exceeded
,但是驱动器上有足够的空间和读/写权限)。
#include <aio.h>
#include <stdio.h>
char CONTENT[] = "asdf;";
const int LENGTH = 5;
struct aiocb createIoRequest(int fd,
off_t offset,
volatile void * content,
size_t length){
struct aiocb ret; // <-- not initialized. Will lead to an error ( see answer)
{
ret.aio_fildes = fd;
ret.aio_offset = offset;
ret.aio_buf = content;
ret.aio_nbytes = length;
}
return ret;
}
int main(){
FILE * file = fopen("outfile.txt","w");
int fd = fileno(file);
{
struct aiocb op = createIoRequest(fd,0,CONTENT,LENGTH);
// schedule write
// for valgrind mem leak output see comments from answer in
// https://stackoverflow.com/questions/4248720/aio-h-aio-read-and-write-memory-leak
int ret = aio_write(&op);
printf("aio_write 1: %d\n",ret);
// wait until everything is done
{
const struct aiocb * aiolist[1];
aiolist[0] = &op;
int ret = aio_suspend(aiolist,1,NULL);
printf("aio_suspend: %d\n",ret);
// report possible errors
{
ret = aio_error(&op);
printf("errno 1: %d\n",ret);
}
}
}
fclose(file);
return 0;
}
使用valgrind报告Conditional jump or move depends on uninitialised value(s)
检查代码
aiocb未初始化。
下面的程序将asdf;
写入outfile.txt
。在createIoRequest()
#include <aio.h>
#include <stdio.h>
char CONTENT[] = "asdf;";
const int LENGTH = 5;
struct aiocb createIoRequest(int fd,
off_t offset,
volatile void * content,
size_t length){
// create and initialize the aiocb structure.
// If we don't init to 0, we have undefined behavior.
// E.g. through sigevent op.aio_sigevent there could be
// a callback function being set, that the program
// tries to call - which will then fail.
struct aiocb ret = {0};
{
ret.aio_fildes = fd;
ret.aio_offset = offset;
ret.aio_buf = content;
ret.aio_nbytes = length;
}
return ret;
}
int main(){
FILE * file = fopen("outfile.txt","w");
int fd = fileno(file);
{
struct aiocb op = createIoRequest(fd,0,CONTENT,LENGTH);
// schedule write
// for valgrind mem leak output see comments from answer in
// https://stackoverflow.com/questions/4248720/aio-h-aio-read-and-write-memory-leak
int ret = aio_write(&op);
printf("aio_write 1: %d\n",ret);
// wait until everything is done
{
const struct aiocb * aiolist[1];
aiolist[0] = &op;
int ret = aio_suspend(aiolist,1,NULL);
printf("aio_suspend: %d\n",ret);
// report possible errors
{
ret = aio_error(&op);
printf("errno 1: %d\n",ret);
}
}
}
fclose(file);
return 0;
}
下面的程序只是将上面的程序扩展为对文件进行两次异步写入
#include <aio.h>
#include <stdio.h>
char CONTENT[] = "asdf;";
const int LENGTH = 5;
struct aiocb createIoRequest(int fd,
off_t offset,
volatile void * content,
size_t length){
// create and initialize the aiocb structure.
// If we don't init to 0, we have undefined behavior.
// E.g. through sigevent op.aio_sigevent there could be
// a callback function being set, that the program
// tries to call - which will then fail.
struct aiocb ret = {0};
{
ret.aio_fildes = fd;
ret.aio_offset = offset;
ret.aio_buf = content;
ret.aio_nbytes = length;
}
return ret;
}
int main(){
FILE * file = fopen("outfile.txt","w");
int fd = fileno(file);
{
struct aiocb op = createIoRequest(fd,0,CONTENT,LENGTH);
struct aiocb op2 = createIoRequest(fd,LENGTH,CONTENT,LENGTH);
// schedule write
// for valgrind mem leak output see comments from answer in
// https://stackoverflow.com/questions/4248720/aio-h-aio-read-and-write-memory-leak
int ret = aio_write(&op);
printf("aio_write 1: %d\n",ret);
ret = aio_write(&op2);
printf("aio_write 2: %d\n",ret);
// wait until everything is done
{
const int OPs = 2;
const struct aiocb * aiolist[OPs];
aiolist[0] = &op;
aiolist[1] = &op2;
int ret = aio_suspend(aiolist,OPs,NULL);
printf("aio_suspend: %d\n",ret);
// report possible errors
{
ret = aio_error(&op);
printf("errno 1: %d\n",ret);
ret = aio_error(&op2);
printf("errno 2: %d\n",ret);
// error codes can be checked in <errno.h>
}
}
}
fclose(file);
return 0;
}