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#pragma once
///@file
#include <thread>
#include <atomic>
#include <cstdlib>
#include <poll.h>
#include <sys/types.h>
#include <unistd.h>
#include <signal.h>
#include "error.hh"
#include "file-descriptor.hh"
#include "signals.hh"
namespace nix {
class MonitorFdHup
{
private:
std::thread thread;
/**
* Pipe used to interrupt the poll()ing in the monitoring thread.
*/
Pipe terminatePipe;
std::atomic_bool quit = false;
public:
MonitorFdHup(int fd)
{
terminatePipe.create();
auto &quit_ = this->quit;
int terminateFd = terminatePipe.readSide.get();
thread = std::thread([fd, terminateFd, &quit_]() {
while (!quit_) {
/* Wait indefinitely until a POLLHUP occurs. */
struct pollfd fds[2];
fds[0].fd = fd;
// There is a POSIX violation on macOS: you have to listen for
// at least POLLHUP to receive HUP events for a FD. POSIX says
// this is not so, and you should just receive them regardless,
// however, as of our testing on macOS 14.5, the events do not
// get delivered in such a case.
//
// This is allegedly filed as rdar://37537852.
//
// Relevant code, which backs this up:
// https://github.com/apple-oss-distributions/xnu/blob/94d3b452840153a99b38a3a9659680b2a006908e/bsd/kern/sys_generic.c#L1751-L1758
fds[0].events = POLLHUP;
fds[1].fd = terminateFd;
fds[1].events = POLLIN;
auto count = poll(fds, 2, -1);
if (count == -1) {
if (errno == EINTR || errno == EAGAIN) {
// These are best dealt with by just trying again.
continue;
} else {
throw SysError("in MonitorFdHup poll()");
}
}
/* This shouldn't happen, but can on macOS due to a bug.
See rdar://37550628.
This may eventually need a delay or further
coordination with the main thread if spinning proves
too harmful.
*/
if (count == 0) continue;
if (fds[0].revents & POLLHUP) {
triggerInterrupt();
break;
}
// No reason to actually look at the pipe FD if that's what
// woke us, the only thing that actually matters is the quit
// flag.
if (quit_) {
break;
}
// On macOS, it is possible (although not observed on macOS
// 14.5) that in some limited cases on buggy kernel versions,
// all the non-POLLHUP events for the socket get delivered.
// Sleeping avoids pointlessly spinning a thread on those.
sleep(1);
}
});
};
~MonitorFdHup()
{
quit = true;
// Poke the thread out of its poll wait
writeFull(terminatePipe.writeSide.get(), "*", false);
if (thread.joinable()) {
thread.join();
}
}
};
}
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