According to POSIX, FIFO allows multiple readers / writers. However, it appears
that Cygwin's implementation only allows for multiple readers and single writer.
The following code fails on Cygwin but passes on Linux (tested on Ubuntu and
Debian). Note that this code is to replicate an issue of a bigger project that
relies on FIFO for interprocess synchronizations.
#include <unistd.h>
#include <fcntl.h>
#include <cerrno>
#include <stdlib.h>
#include <string>
#include <iostream>
#include <sys/types.h>
#include <sys/stat.h>
int main()
{
std::string n = "/tmp/test";
int err;
err = mkfifo(n.c_str(), 0666);
if (err == -1)
{
std::cout << "mkfifo error" << std::endl;
return 0;
}
int pipefd[4];
pipefd[0] = open(n.c_str(), O_RDONLY | O_NONBLOCK);
if (pipefd[0] == -1)
{
std::cout << "open 1 error" << std::endl;
return 0;
}
pipefd[1] = open(n.c_str(), O_WRONLY | O_NONBLOCK);
if (pipefd[1] == -1)
{
std::cout << "open 2 error" << std::endl;
return 0;
}
pipefd[2] = open(n.c_str(), O_RDONLY | O_NONBLOCK); // fails - ENXIO
if (pipefd[2] == -1)
{
std::cout << "open 3 error" << std::endl;
return 0;
}
pipefd[3] = open(n.c_str(), O_WRONLY | O_NONBLOCK); // fails - ENXIO
if (pipefd[3] == -1)
{
std::cout << "open 4 error" << std::endl;
return 0;
}
for (int i=0; i<4; i++)
close(pipefd[i]);
unlink(n.c_str());
return 0;
}
Expected output (as tested on Ubuntu and Debian):
(nil)
Actual output:
open 3 error
--
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