llvm-6502/lib/Support/LockFileManager.cpp
Rafael Espindola 8d230cd536 Misc cleanups to the FileSytem api.
The main difference is the removal of

std::error_code exists(const Twine &path, bool &result);

It was an horribly redundant interface since a file not existing is also a valid
error_code. Now we have an access function that returns just an error_code. This
is the only function that has to be implemented for Unix and Windows. The
functions can_write, exists and can_execute an now just wrappers.

One still has to be very careful using these function to avoid introducing
race conditions (Time of check to time of use).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@217625 91177308-0d34-0410-b5e6-96231b3b80d8
2014-09-11 20:30:02 +00:00

266 lines
7.3 KiB
C++

//===--- LockFileManager.cpp - File-level Locking Utility------------------===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
#include "llvm/Support/LockFileManager.h"
#include "llvm/ADT/STLExtras.h"
#include "llvm/ADT/StringExtras.h"
#include "llvm/Support/Errc.h"
#include "llvm/Support/FileSystem.h"
#include "llvm/Support/MemoryBuffer.h"
#include "llvm/Support/Path.h"
#include "llvm/Support/raw_ostream.h"
#include <sys/stat.h>
#include <sys/types.h>
#if LLVM_ON_WIN32
#include <windows.h>
#endif
#if LLVM_ON_UNIX
#include <unistd.h>
#endif
using namespace llvm;
/// \brief Attempt to read the lock file with the given name, if it exists.
///
/// \param LockFileName The name of the lock file to read.
///
/// \returns The process ID of the process that owns this lock file
Optional<std::pair<std::string, int> >
LockFileManager::readLockFile(StringRef LockFileName) {
// Read the owning host and PID out of the lock file. If it appears that the
// owning process is dead, the lock file is invalid.
ErrorOr<std::unique_ptr<MemoryBuffer>> MBOrErr =
MemoryBuffer::getFile(LockFileName);
if (!MBOrErr) {
sys::fs::remove(LockFileName);
return None;
}
MemoryBuffer &MB = *MBOrErr.get();
StringRef Hostname;
StringRef PIDStr;
std::tie(Hostname, PIDStr) = getToken(MB.getBuffer(), " ");
PIDStr = PIDStr.substr(PIDStr.find_first_not_of(" "));
int PID;
if (!PIDStr.getAsInteger(10, PID)) {
auto Owner = std::make_pair(std::string(Hostname), PID);
if (processStillExecuting(Owner.first, Owner.second))
return Owner;
}
// Delete the lock file. It's invalid anyway.
sys::fs::remove(LockFileName);
return None;
}
bool LockFileManager::processStillExecuting(StringRef Hostname, int PID) {
#if LLVM_ON_UNIX && !defined(__ANDROID__)
char MyHostname[256];
MyHostname[255] = 0;
MyHostname[0] = 0;
gethostname(MyHostname, 255);
// Check whether the process is dead. If so, we're done.
if (MyHostname == Hostname && getsid(PID) == -1 && errno == ESRCH)
return false;
#endif
return true;
}
LockFileManager::LockFileManager(StringRef FileName)
{
this->FileName = FileName;
if (std::error_code EC = sys::fs::make_absolute(this->FileName)) {
Error = EC;
return;
}
LockFileName = this->FileName;
LockFileName += ".lock";
// If the lock file already exists, don't bother to try to create our own
// lock file; it won't work anyway. Just figure out who owns this lock file.
if ((Owner = readLockFile(LockFileName)))
return;
// Create a lock file that is unique to this instance.
UniqueLockFileName = LockFileName;
UniqueLockFileName += "-%%%%%%%%";
int UniqueLockFileID;
if (std::error_code EC = sys::fs::createUniqueFile(
UniqueLockFileName.str(), UniqueLockFileID, UniqueLockFileName)) {
Error = EC;
return;
}
// Write our process ID to our unique lock file.
{
raw_fd_ostream Out(UniqueLockFileID, /*shouldClose=*/true);
#if LLVM_ON_UNIX
// FIXME: move getpid() call into LLVM
char hostname[256];
hostname[255] = 0;
hostname[0] = 0;
gethostname(hostname, 255);
Out << hostname << ' ' << getpid();
#else
Out << "localhost 1";
#endif
Out.close();
if (Out.has_error()) {
// We failed to write out PID, so make up an excuse, remove the
// unique lock file, and fail.
Error = make_error_code(errc::no_space_on_device);
sys::fs::remove(UniqueLockFileName.c_str());
return;
}
}
while (1) {
// Create a link from the lock file name. If this succeeds, we're done.
std::error_code EC =
sys::fs::create_link(UniqueLockFileName.str(), LockFileName.str());
if (!EC)
return;
if (EC != errc::file_exists) {
Error = EC;
return;
}
// Someone else managed to create the lock file first. Read the process ID
// from the lock file.
if ((Owner = readLockFile(LockFileName))) {
// Wipe out our unique lock file (it's useless now)
sys::fs::remove(UniqueLockFileName.str());
return;
}
if (!sys::fs::exists(LockFileName.str())) {
// The previous owner released the lock file before we could read it.
// Try to get ownership again.
continue;
}
// There is a lock file that nobody owns; try to clean it up and get
// ownership.
if ((EC = sys::fs::remove(LockFileName.str()))) {
Error = EC;
return;
}
}
}
LockFileManager::LockFileState LockFileManager::getState() const {
if (Owner)
return LFS_Shared;
if (Error)
return LFS_Error;
return LFS_Owned;
}
LockFileManager::~LockFileManager() {
if (getState() != LFS_Owned)
return;
// Since we own the lock, remove the lock file and our own unique lock file.
sys::fs::remove(LockFileName.str());
sys::fs::remove(UniqueLockFileName.str());
}
LockFileManager::WaitForUnlockResult LockFileManager::waitForUnlock() {
if (getState() != LFS_Shared)
return Res_Success;
#if LLVM_ON_WIN32
unsigned long Interval = 1;
#else
struct timespec Interval;
Interval.tv_sec = 0;
Interval.tv_nsec = 1000000;
#endif
// Don't wait more than five minutes for the file to appear.
unsigned MaxSeconds = 300;
bool LockFileGone = false;
do {
// Sleep for the designated interval, to allow the owning process time to
// finish up and remove the lock file.
// FIXME: Should we hook in to system APIs to get a notification when the
// lock file is deleted?
#if LLVM_ON_WIN32
Sleep(Interval);
#else
nanosleep(&Interval, nullptr);
#endif
bool LockFileJustDisappeared = false;
// If the lock file is still expected to be there, check whether it still
// is.
if (!LockFileGone) {
if (sys::fs::access(LockFileName.c_str(), sys::fs::AccessMode::Exist) ==
errc::no_such_file_or_directory) {
LockFileGone = true;
LockFileJustDisappeared = true;
}
}
// If the lock file is no longer there, check if the original file is
// available now.
if (LockFileGone) {
if (sys::fs::exists(FileName.str())) {
return Res_Success;
}
// The lock file is gone, so now we're waiting for the original file to
// show up. If this just happened, reset our waiting intervals and keep
// waiting.
if (LockFileJustDisappeared) {
MaxSeconds = 5;
#if LLVM_ON_WIN32
Interval = 1;
#else
Interval.tv_sec = 0;
Interval.tv_nsec = 1000000;
#endif
continue;
}
}
// If we're looking for the lock file to disappear, but the process
// owning the lock died without cleaning up, just bail out.
if (!LockFileGone &&
!processStillExecuting((*Owner).first, (*Owner).second)) {
return Res_OwnerDied;
}
// Exponentially increase the time we wait for the lock to be removed.
#if LLVM_ON_WIN32
Interval *= 2;
#else
Interval.tv_sec *= 2;
Interval.tv_nsec *= 2;
if (Interval.tv_nsec >= 1000000000) {
++Interval.tv_sec;
Interval.tv_nsec -= 1000000000;
}
#endif
} while (
#if LLVM_ON_WIN32
Interval < MaxSeconds * 1000
#else
Interval.tv_sec < (time_t)MaxSeconds
#endif
);
// Give up.
return Res_Timeout;
}