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#include "lix/libstore/pathlocks.hh"
#include "lix/libutil/async.hh"
#include "lix/libutil/c-calls.hh"
#include "lix/libutil/file-descriptor.hh"
#include "lix/libutil/logging.hh"
#include "lix/libutil/signals.hh"
#include "lix/libutil/types.hh"
#include <cerrno>
#include <fcntl.h>
#include <kj/common.h>
#include <optional>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/file.h>
namespace nix {
AutoCloseFD openLockFile(const Path & path, bool create)
{
AutoCloseFD fd{sys::open(path, O_CLOEXEC | O_RDWR | (create ? O_CREAT : 0), 0600)};
if (!fd && (create || errno != ENOENT))
throw SysError("opening lock file '%1%'", path);
return fd;
}
static int convertLockType(LockType lockType)
{
if (lockType == ltRead) return LOCK_SH;
else if (lockType == ltWrite) return LOCK_EX;
else abort();
}
void lockFile(int fd, LockType lockType, NeverAsync)
{
int type = convertLockType(lockType);
while (flock(fd, type) != 0) {
checkInterrupt();
if (errno != EINTR)
throw SysError("acquiring lock");
}
}
static kj::Promise<Result<void>> lockFileAsyncInner(int fd, LockType lockType)
try {
// start a thread to lock the file synchronously, waiting for an
// INTERRUPT_NOTIFY_SIGNAL to signal that the call was canceled.
int type = convertLockType(lockType);
auto pfp = kj::newPromiseAndCrossThreadFulfiller<Result<void>>();
std::thread locker([&] {
while (flock(fd, type) != 0 && pfp.fulfiller->isWaiting()) {
if (errno != EINTR) {
pfp.fulfiller->fulfill(std::make_exception_ptr(SysError("acquiring lock")));
return;
}
}
pfp.fulfiller->fulfill(result::success());
});
auto cancel = kj::defer([&] {
pthread_kill(locker.native_handle(), INTERRUPT_NOTIFY_SIGNAL);
locker.join();
});
TRY_AWAIT(makeInterruptible(std::move(pfp.promise)));
locker.join();
cancel.cancel();
co_return result::success();
} catch (...) {
co_return result::current_exception();
}
kj::Promise<Result<void>> lockFileAsync(int fd, LockType lockType)
try {
if (tryLockFile(fd, lockType)) {
return {result::success()};
}
return lockFileAsyncInner(fd, lockType);
} catch (...) {
return {result::current_exception()};
}
bool tryLockFile(int fd, LockType lockType)
{
int type = convertLockType(lockType);
while (flock(fd, type | LOCK_NB) != 0) {
checkInterrupt();
if (errno == EWOULDBLOCK) return false;
if (errno != EINTR)
throw SysError("acquiring lock");
}
return true;
}
void unlockFile(int fd)
{
while (flock(fd, LOCK_UN) != 0) {
if (errno != EINTR) {
throw SysError("releasing lock");
}
}
}
static bool isPathLockValid(AutoCloseFD & fd, const Path & lockPath)
{
/* Check that the lock file hasn't become stale (i.e.,
hasn't been unlinked). */
struct stat st;
if (fstat(fd.get(), &st) == -1)
throw SysError("statting lock file '%1%'", lockPath);
if (st.st_nlink == 0) {
/* This lock file has been unlinked, so we're holding
a lock on a deleted file. This means that other
processes may create and acquire a lock on
`lockPath', and proceed. So we must retry. */
debug("open lock file '%1%' has become stale", lockPath);
return false;
} else {
return true;
}
}
std::optional<PathLock>
PathLock::lockImpl(const Path & path, std::string_view waitMsg, bool wait, NeverAsync)
{
Path lockPath = path + ".lock";
debug("locking path '%1%'", path);
while (1) {
/* Open/create the lock file. */
auto fd = openLockFile(lockPath, true);
/* Acquire an exclusive lock. */
if (!tryLockFile(fd.get(), ltWrite)) {
if (wait) {
if (waitMsg != "") {
printError("%1%", Uncolored(waitMsg));
}
lockFile(fd.get(), ltWrite);
} else {
return std::nullopt;
}
}
debug("lock acquired on '%1%'", lockPath);
if (isPathLockValid(fd, lockPath))
return PathLock{std::move(fd), lockPath};
}
}
kj::Promise<Result<PathLock>> lockPathAsync(const Path & path, std::string_view waitMsg)
try {
Path lockPath = path + ".lock";
debug("locking path '%1%'", path);
while (1) {
auto fd = openLockFile(lockPath, true);
TRY_AWAIT(lockFileAsync(fd.get(), ltWrite));
debug("lock acquired on '%1%'", lockPath);
if (isPathLockValid(fd, lockPath))
co_return PathLock{std::move(fd), lockPath};
}
} catch (...) {
co_return result::current_exception();
}
PathLock lockPath(const Path & path, std::string_view waitMsg, NeverAsync)
{
return std::move(*PathLock::lockImpl(path, waitMsg, true));
}
std::optional<PathLock> tryLockPath(const Path & path)
{
return PathLock::lockImpl(path, "", false, always_progresses);
}
static std::optional<PathLocks>
lockPathsImpl(const PathSet & paths, std::string_view waitMsg, bool wait, NeverAsync = {})
{
PathLocks result;
/* Acquire the lock for each path in sorted order. This ensures
that locks are always acquired in the same order, thus
preventing deadlocks. */
for (auto & path : paths) {
if (wait) {
result.push_back(lockPath(path, waitMsg));
} else if (auto p = tryLockPath(path); p) {
result.push_back(std::move(*p));
} else {
return std::nullopt;
}
}
return result;
}
PathLocks lockPaths(const PathSet & paths, std::string_view waitMsg, NeverAsync)
{
return std::move(*lockPathsImpl(paths, waitMsg, true));
}
std::optional<PathLocks> tryLockPaths(const PathSet & paths)
{
return lockPathsImpl(paths, "", false, always_progresses);
}
PathLock::~PathLock()
{
try {
unlock();
} catch (...) {
ignoreExceptionInDestructor();
}
}
void PathLock::unlock()
{
if (fd) {
// delete the file. if another file descriptor is used to acquire a lock on
// this file it will figure out that the file is stale once it calls stat()
// and inspects the link count. if unlink fails we merely leave around some
// stale lock file paths that can be reused or cleaned up by other threads.
(void) sys::unlink(path);
// clobber file contents for compatibility wither other nix implementations
writeFull(fd.get(), "d");
if (close(fd.release()) == -1) {
printError("error (ignored): cannot close lock file on '%1%'", path);
}
debug("lock released on '%1%'", path);
}
}
FdLock::FdLock(AutoCloseFD & fd, LockType lockType, DontWait)
{
if (tryLockFile(fd.get(), lockType)) {
this->fd.reset(&fd);
}
}
FdLock::FdLock(AutoCloseFD & fd, LockType lockType, std::string_view waitMsg, NeverAsync)
{
if (!tryLockFile(fd.get(), lockType)) {
printInfo("%s", Uncolored(waitMsg));
lockFile(fd.get(), lockType);
this->fd.reset(&fd);
}
}
kj::Promise<Result<FdLock>>
FdLock::lockAsync(AutoCloseFD & fd, LockType lockType, std::string_view waitMsg)
try {
if (!tryLockFile(fd.get(), lockType)) {
printInfo("%s", Uncolored(waitMsg));
TRY_AWAIT(lockFileAsyncInner(fd.get(), lockType));
}
co_return FdLock{fd};
} catch (...) {
co_return result::current_exception();
}
}
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