bool tryLock(const Zstring& lockfilepath) //throw FileError
{
#ifdef ZEN_WIN
#ifdef TODO_MinFFS_ActivatePriviledge
try { activatePrivilege(SE_BACKUP_NAME); }
catch (const FileError&) {}
try { activatePrivilege(SE_RESTORE_NAME); }
catch (const FileError&) {}
#endif//TODO_MinFFS_ActivatePriviledge
const HANDLE fileHandle = ::CreateFile(applyLongPathPrefix(lockfilepath).c_str(), //_In_ LPCTSTR lpFileName,
//use both when writing over network, see comment in file_io.cpp
GENERIC_READ | GENERIC_WRITE, //_In_ DWORD dwDesiredAccess,
FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE, //_In_ DWORD dwShareMode,
nullptr, //_In_opt_ LPSECURITY_ATTRIBUTES lpSecurityAttributes,
CREATE_NEW, //_In_ DWORD dwCreationDisposition,
FILE_ATTRIBUTE_NORMAL | FILE_FLAG_BACKUP_SEMANTICS, //_In_ DWORD dwFlagsAndAttributes,
nullptr); //_In_opt_ HANDLE hTemplateFile
if (fileHandle == INVALID_HANDLE_VALUE)
{
const DWORD ec = ::GetLastError(); //copy before directly/indirectly making other system calls!
if (ec == ERROR_FILE_EXISTS || //confirmed to be used
ec == ERROR_ALREADY_EXISTS) //comment on msdn claims, this one is used on Windows Mobile 6
return false;
throw FileError(replaceCpy(_("Cannot write file %x."), L"%x", fmtPath(lockfilepath)), formatSystemError(L"CreateFile", ec));
}
ScopeGuard guardLockFile = zen::makeGuard([&] { removeFile(lockfilepath); });
FileOutput fileOut(fileHandle, lockfilepath); //pass handle ownership
//be careful to avoid CreateFile() + CREATE_ALWAYS on a hidden file -> see file_io.cpp
//=> we don't need it that badly //::SetFileAttributes(applyLongPathPrefix(lockfilepath).c_str(), FILE_ATTRIBUTE_HIDDEN); //(try to) hide it
#elif defined ZEN_LINUX || defined ZEN_MAC
const mode_t oldMask = ::umask(0); //important: we want the lock file to have exactly the permissions specified
ZEN_ON_SCOPE_EXIT(::umask(oldMask));
//O_EXCL contains a race condition on NFS file systems: http://linux.die.net/man/2/open
const int fileHandle = ::open(lockfilepath.c_str(), O_CREAT | O_EXCL | O_WRONLY,
S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH);
if (fileHandle == -1)
{
if (errno == EEXIST)
return false;
else
THROW_LAST_FILE_ERROR(replaceCpy(_("Cannot write file %x."), L"%x", fmtPath(lockfilepath)), L"open");
}
ScopeGuard guardLockFile = zen::makeGuard([&] { removeFile(lockfilepath); });
FileOutput fileOut(fileHandle, lockfilepath); //pass handle ownership
#endif
//write housekeeping info: user, process info, lock GUID
ByteArray binStream = [&]
{
MemStreamOut streamOut;
LockInformation(FromCurrentProcess()).toStream(streamOut);
return streamOut.ref();
}();
if (!binStream.empty())
fileOut.write(&*binStream.begin(), binStream.size()); //throw FileError
guardLockFile.dismiss(); //lockfile created successfully
return true;
}
