我正在尝试使用 poll(2)在各种平台上的 FIFO 上,但是(与 Linux、Solaris、AIX 相比),HP-UX 的行为与其他平台有些不同。
下面的代码创建一个 FIFO(命名管道)并以 3 秒超时轮询它。由于此代码不会写入 FIFO,因此我预计轮询结果将为 0。
#include <fcntl.h>
#include <poll.h>
#include <signal.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
#include <errno.h>
#include <inttypes.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#if defined(CLOCK_MONOTONIC)
#define MY_CLOCK_TIME CLOCK_MONOTONIC
#elif defined(CLOCK_REALTIME)
#define MY_CLOCK_TIME CLOCK_REALTIME
#else
#error neither CLOCK_REALTIME nor CLOCK_MONOTONIC defined.
#endif
#define HANDLE_ERROR(expr, msg) \
do \
{ \
if ((expr) < 0) \
{ \
perror(msg); \
exit(EXIT_FAILURE); \
} \
} while (0);
namespace {
const char pipename[] = "pipe";
template <size_t N>
struct type_of_size
{
typedef char type[N];
};
template <typename T, size_t Size>
typename type_of_size<Size>::type& sizeof_array_helper(T (&)[Size]);
#define SIZE_OF_ARR(pArray) sizeof(sizeof_array_helper(pArray))
int my_unlink(const char* name)
{
int result = unlink(name);
if (result < 0)
{
if (errno == ENOENT)
{
result = 0;
errno = 0;
}
}
return result;
}
double timediff(const struct timespec& t1, const struct timespec& t2)
{
return static_cast<double>(static_cast<int64_t>(
(t1.tv_sec - t2.tv_sec) * 1000000000LL + (t1.tv_nsec - t2.tv_nsec))) /
1000000000LL;
}
} // namespace
int main()
{
HANDLE_ERROR(my_unlink(pipename), "unlink");
HANDLE_ERROR(mkfifo(pipename, 0600), "mkfifo");
int result = 0;
int poll_timeout = 3000; // 3s
struct timespec before;
memset(&before, 0, sizeof(struct timespec));
struct timespec after;
memset(&after, 0, sizeof(struct timespec));
int fd = open(pipename, O_RDONLY | O_NONBLOCK);
HANDLE_ERROR((fd < 0), "open");
pollfd fds[1];
memset(fds, 0, sizeof(pollfd) * SIZE_OF_ARR(fds));
fds[0].fd = fd;
fds[0].events = POLLIN;
HANDLE_ERROR(clock_gettime(MY_CLOCK_TIME, &before), "clock_gettime");
#ifdef USE_FAKE_OPEN
int fakeopen_fd = open(pipename, O_WRONLY | O_NONBLOCK);
HANDLE_ERROR((fakeopen_fd < 0), "open");
#endif
result = poll(fds, SIZE_OF_ARR(fds), poll_timeout);
memset(&after, 0, sizeof(struct timespec));
HANDLE_ERROR(clock_gettime(MY_CLOCK_TIME, &after), "clock_gettime");
double interval = timediff(after, before);
printf("call interval: %.3f, poll result: %d, errr: %s\n", interval, result, strerror(errno));
#ifdef USE_FAKE_OPEN
close(fakeopen_fd);
#endif
close(fd);
return (interval > 2.0) ? EXIT_SUCCESS : EXIT_FAILURE;
}
在 Linux、Solaris 10、AIX 7.1 上,它按预期工作(调用间隔:3.000,轮询结果:0,errr:错误 0
),但 HP-UX(11.31) 则不然遵守超时参数并立即返回(调用间隔:0.000,轮询结果:1,errr:错误0
)。
如果我在轮询读取之前打开 FIFO 进行写入(定义USE_FAKE_OPEN
),即使对于 HP-UX,它也会按预期工作。
是什么导致了这种行为?
HP-UX 的投票是否符合 POSIX 标准?
最佳答案
好吧,编程有一条规则:"It's Always Your Fault (Select Isn't Broken)" ,但 HP 表示他们的 documentation for HP-UX patch PHKL_41419 中的对 FIFO 的轮询已损坏 :
poll(2) sets POLLIN (data ready for reading)event even if there is no writer at the other end when a FIFO is opened with O_RDONLY in non blocking mode(O_NONBLOCK set).
案件结案。
关于c++ - HP-UX 中对 FIFO 的轮询立即返回,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/49917407/