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// Copyright (c) 2009-2010 Satoshi Nakamoto
// Copyright (c) 2009-2020 The Bitcoin Core developers
// Distributed under the MIT software license, see the accompanying
// file COPYING or http://www.opensource.org/licenses/mit-license.php.
#include <shutdown.h>
#include <config/bitcoin-config.h>
#include <assert.h>
#include <atomic>
#ifdef WIN32
#include <condition_variable>
#else
#include <errno.h>
#include <fcntl.h>
#include <unistd.h>
#endif
static std::atomic<bool> fRequestShutdown(false);
#ifdef WIN32
/** On windows it is possible to simply use a condition variable. */
std::mutex g_shutdown_mutex;
std::condition_variable g_shutdown_cv;
#else
/** On UNIX-like operating systems use the self-pipe trick.
* Index 0 will be the read end of the pipe, index 1 the write end.
*/
static int g_shutdown_pipe[2] = {-1, -1};
#endif
bool InitShutdownState()
{
#ifndef WIN32
#if HAVE_O_CLOEXEC
// If we can, make sure that the file descriptors are closed on exec()
// to prevent interference.
if (pipe2(g_shutdown_pipe, O_CLOEXEC) != 0) {
return false;
}
#else
if (pipe(g_shutdown_pipe) != 0) {
return false;
}
#endif
#endif
return true;
}
void StartShutdown()
{
#ifdef WIN32
std::unique_lock<std::mutex> lk(g_shutdown_mutex);
fRequestShutdown = true;
g_shutdown_cv.notify_one();
#else
// This must be reentrant and safe for calling in a signal handler, so using a condition variable is not safe.
// Make sure that the token is only written once even if multiple threads call this concurrently or in
// case of a reentrant signal.
if (!fRequestShutdown.exchange(true)) {
// Write an arbitrary byte to the write end of the shutdown pipe.
const char token = 'x';
while (true) {
int result = write(g_shutdown_pipe[1], &token, 1);
if (result < 0) {
// Failure. It's possible that the write was interrupted by another signal.
// Other errors are unexpected here.
assert(errno == EINTR);
} else {
assert(result == 1);
break;
}
}
}
#endif
}
void AbortShutdown()
{
if (fRequestShutdown) {
// Cancel existing shutdown by waiting for it, this will reset condition flags and remove
// the shutdown token from the pipe.
WaitForShutdown();
}
fRequestShutdown = false;
}
bool ShutdownRequested()
{
return fRequestShutdown;
}
void WaitForShutdown()
{
#ifdef WIN32
std::unique_lock<std::mutex> lk(g_shutdown_mutex);
g_shutdown_cv.wait(lk, [] { return fRequestShutdown.load(); });
#else
char token;
while (true) {
int result = read(g_shutdown_pipe[0], &token, 1);
if (result < 0) {
// Failure. Check if the read was interrupted by a signal.
// Other errors are unexpected here.
assert(errno == EINTR);
} else {
assert(result == 1);
break;
}
}
#endif
}
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