读取在命名管道上不阻塞
我有以下 C 代码，它从管道读取，然后应该阻塞，但它永远不会阻塞
int pipe_fd;
int res;
int open_mode = O_RDONLY;
char buf[100];
int bytes_read = 0;
memset (buf, '\0', sizeof(buf));
pipe_fd = open(FIFO_NAME, open_mode);
if (access(FIFO_NAME, F_OK) == -1)
{
res = mkfifo(FIFO_NAME, 0777);
if (res != 0)
{
fprintf (stderr, "Could not create fifo %s\n", FIFO_NAME);
exit (EXIT_FAILURE);
}
}
for(;;)
{
do
{
res = read(pipe_fd, buf, sizeof(buf));
bytes_read += res;
}while (res > 0);
// process data then go back and block
............
}
它是由 bash 脚本中的某些代码发送的一个简单缓冲区，如“./test 1”
#!/bin/bash
pipe=/tmp/pipe
if [[ ! -p $pipe ]]; then
echo "Reader not running"
exit 1
fi
if [[ "$1" ]]; then
echo "some string" >$pipe
else
echo "q" >$pipe
fi
我在 gdb 中运行 C 代码程序最初它确实会阻塞读取，但是一旦我调用 bash 脚本，C 代码就不再阻塞，它确实成功地读取了数据 缓冲区，然后每次读取时都会读取 0 个字节，因此不确定为什么它不再阻塞。另一端正确接收到“某些字符串”数据。
我只需要它坐在那里等待数据处理，然后返回并等待更多
i have the following bit of C code which reads from a pipe and then should block but it never blocks
int pipe_fd;
int res;
int open_mode = O_RDONLY;
char buf[100];
int bytes_read = 0;
memset (buf, '\0', sizeof(buf));
pipe_fd = open(FIFO_NAME, open_mode);
if (access(FIFO_NAME, F_OK) == -1)
{
res = mkfifo(FIFO_NAME, 0777);
if (res != 0)
{
fprintf (stderr, "Could not create fifo %s\n", FIFO_NAME);
exit (EXIT_FAILURE);
}
}
for(;;)
{
do
{
res = read(pipe_fd, buf, sizeof(buf));
bytes_read += res;
}while (res > 0);
// process data then go back and block
............
}
It is sent a simple buffer by some code in a bash script like this './test 1'
#!/bin/bash
pipe=/tmp/pipe
if [[ ! -p $pipe ]]; then
echo "Reader not running"
exit 1
fi
if [[ "$1" ]]; then
echo "some string" >$pipe
else
echo "q" >$pipe
fi
I run the C code program in gdb and initially it does block on the read but as soon as i call the bash script the C code no longer blocks , it does successfully read the data from
the buffer and then each time it reads there are 0 bytes read so not sure why its no longer blocking. The 'some string' data is correctly received at the other side.
I just need it to sit there waiting for data process it and then go back and wait for more
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评论（3）
0表示 EOF。仅当有进程连接到 FIFO 进行读写时，才能对 FIFO 进行读写。当不再有写入器（您的 shell 脚本终止）时，读取器会通过返回 EOF 的read()收到通知。FIFO 的行为方式与 shell 管道逻辑兼容，例如：
如果
read()不会返回 EOF，则第二个cat将永远阻塞。在您的 C 程序中，您必须在
read()之后重新open()FIFO > 第一次返回EOF。PS 为您找到了非常好的 FIFO 摘要。检查第二页上的表格。
0means EOF. FIFO can be read or written only when there are processes connected to it for both reading and writing. When there are no more writers (your shell scripts terminated) readers are notified about that throughread()returning the EOF.FIFOs behave that way to be compatible with shell pipe logic e.g.:
If
read()will not return EOF, the secondcatwould block forever.In your C program you have to re
open()the FIFO afterread()returned the EOF first time.P.S. Found quite nice FIFO summary for your. Check the table on the second page.
您的 bash 脚本关闭管道，因此 C 遇到“eof”条件
your bash script closes the pipe so the C is getting an "eof" condition
我认为每次回显某些内容时编写侧 shell 脚本都会关闭管道。
因此，写入脚本需要打开管道并重复使用打开的描述符来写入内容，最后关闭打开的描述符。
I think write side shell script close the pipe every time when echo something.
So, the write script need to open the pipe and repeatedly use the opended descriptor to write something and close the opended descripter finally.