path: root/lib/dir_lock.cpp

#include "dir_lock.h"
#include <utility>
#include <wx/utils.h>
#include <wx/timer.h>
#include <wx/log.h>
#include <wx/msgdlg.h>
#include <memory>
#include <wx+/string_conv.h>
#include <zen/last_error.h>
#include <zen/thread.h> //includes <boost/thread.hpp>
#include <zen/scope_guard.h>
#include <zen/guid.h>
#include <zen/file_io.h>
#include <zen/assert_static.h>
#include <wx+/serialize.h>
#include <zen/int64.h>
#include <zen/file_handling.h>

#ifdef FFS_WIN
#include <tlhelp32.h>
#include <zen/win.h> //includes "windows.h"
#include <zen/long_path_prefix.h>

#elif defined FFS_LINUX
#include <sys/stat.h>
#include <cerrno>
#include <unistd.h>
#endif

using namespace zen;
using namespace std::rel_ops;


namespace
{
const size_t EMIT_LIFE_SIGN_INTERVAL =  5000; //show life sign;        unit [ms]
const size_t POLL_LIFE_SIGN_INTERVAL =  6000; //poll for life sign;    unit [ms]
const size_t DETECT_EXITUS_INTERVAL  = 30000; //assume abandoned lock; unit [ms]

const char LOCK_FORMAT_DESCR[] = "FreeFileSync";
const int LOCK_FORMAT_VER = 1; //lock file format version
}

//worker thread
class LifeSigns
{
public:
    LifeSigns(const Zstring& lockfilename) : //throw()!!! siehe SharedDirLock()
        lockfilename_(lockfilename) {} //thread safety: make deep copy!

    void operator()() const //thread entry
    {
        try
        {
            while (true)
            {
                boost::thread::sleep(boost::get_system_time() + boost::posix_time::milliseconds(EMIT_LIFE_SIGN_INTERVAL)); //interruption point!

                //actual work
                emitLifeSign(); //throw ()
            }
        }
        catch (const std::exception& e) //exceptions must be catched per thread
        {
            wxSafeShowMessage(wxString(_("An exception occurred!")) + wxT("(Dirlock)"), utf8CvrtTo<wxString>(e.what())); //simple wxMessageBox won't do for threads
        }
    }

    void emitLifeSign() const //try to append one byte...; throw()
    {
        const char buffer[1] = {' '};

#ifdef FFS_WIN
        //ATTENTION: setting file pointer IS required! => use CreateFile/FILE_GENERIC_WRITE + SetFilePointerEx!
        //although CreateFile/FILE_APPEND_DATA without SetFilePointerEx works locally, it MAY NOT work on some network shares creating a 4 gig file!!!

        const HANDLE fileHandle = ::CreateFile(applyLongPathPrefix(lockfilename_).c_str(),
                                               GENERIC_READ | GENERIC_WRITE, //use both when writing over network, see comment in file_io.cpp
                                               FILE_SHARE_READ,
                                               NULL,
                                               OPEN_EXISTING,
                                               FILE_ATTRIBUTE_NORMAL,
                                               NULL);
        if (fileHandle == INVALID_HANDLE_VALUE)
            return;
        ZEN_ON_BLOCK_EXIT(::CloseHandle(fileHandle));

        const LARGE_INTEGER moveDist = {};
        if (!::SetFilePointerEx(fileHandle, //__in       HANDLE hFile,
                                moveDist,   //__in       LARGE_INTEGER liDistanceToMove,
                                NULL,       //__out_opt  PLARGE_INTEGER lpNewFilePointer,
                                FILE_END))  //__in       DWORD dwMoveMethod
            return;

        DWORD bytesWritten = 0;
        ::WriteFile(fileHandle,    //__in         HANDLE hFile,
                    buffer,        //__out        LPVOID lpBuffer,
                    1,             //__in         DWORD nNumberOfBytesToRead,
                    &bytesWritten, //__out_opt    LPDWORD lpNumberOfBytesWritten,
                    NULL);         //__inout_opt  LPOVERLAPPED lpOverlapped

#elif defined FFS_LINUX
        const int fileHandle = ::open(lockfilename_.c_str(), O_WRONLY | O_APPEND); //O_EXCL contains a race condition on NFS file systems: http://linux.die.net/man/2/open
        if (fileHandle == -1)
            return;
        ZEN_ON_BLOCK_EXIT(::close(fileHandle));

        const ssize_t bytesWritten = ::write(fileHandle, buffer, 1);
        (void)bytesWritten;
#endif
    }

private:
    const Zstring lockfilename_; //thread local! atomic ref-count => binary value-type semantics!
};


namespace
{
UInt64 getLockFileSize(const Zstring& filename) //throw FileError, ErrorNotExisting
{
#ifdef FFS_WIN
    WIN32_FIND_DATA fileInfo = {};
    const HANDLE searchHandle = ::FindFirstFile(applyLongPathPrefix(filename).c_str(), &fileInfo);
    if (searchHandle == INVALID_HANDLE_VALUE)
    {
        const DWORD lastError = ::GetLastError();

        std::wstring errorMessage = _("Error reading file attributes:") + L"\n\"" + filename + L"\"" + L"\n\n" + getLastErrorFormatted(lastError);

        if (lastError == ERROR_FILE_NOT_FOUND ||
            lastError == ERROR_PATH_NOT_FOUND ||
            lastError == ERROR_BAD_NETPATH    ||
            lastError == ERROR_NETNAME_DELETED)
            throw ErrorNotExisting(errorMessage);
        else
            throw FileError(errorMessage);
    }

    ::FindClose(searchHandle);

    return zen::UInt64(fileInfo.nFileSizeLow, fileInfo.nFileSizeHigh);

#elif defined FFS_LINUX
    struct ::stat fileInfo = {};
    if (::stat(filename.c_str(), &fileInfo) != 0) //follow symbolic links
    {
        const int lastError = errno;

        std::wstring errorMessage = _("Error reading file attributes:") + L"\n\"" + filename + L"\"" + L"\n\n" + getLastErrorFormatted(lastError);

        if (lastError == ENOENT)
            throw ErrorNotExisting(errorMessage);
        else
            throw FileError(errorMessage);
    }

    return zen::UInt64(fileInfo.st_size);
#endif
}


Zstring deleteAbandonedLockName(const Zstring& lockfilename) //make sure to NOT change file ending!
{
    const size_t pos = lockfilename.rfind(FILE_NAME_SEPARATOR); //search from end
    return pos == Zstring::npos ? Zstr("Del.") + lockfilename :
           Zstring(lockfilename.c_str(), pos + 1) + //include path separator
           Zstr("Del.") +
           afterLast(lockfilename, FILE_NAME_SEPARATOR); //returns the whole string if ch not found
}


namespace
{
//read string from file stream
inline
std::string readString(wxInputStream& stream)  //throw std::exception
{
    const auto strLength = readPOD<std::uint32_t>(stream);
    std::string output;
    if (strLength > 0)
    {
        output.resize(strLength); //throw std::bad_alloc
        stream.Read(&output[0], strLength);
    }
    return output;
}


inline
void writeString(wxOutputStream& stream, const std::string& str)  //write string to filestream
{
    writePOD(stream, static_cast<std::uint32_t>(str.length()));
    stream.Write(str.c_str(), str.length());
}


std::string getComputerId() //returns empty string on error
{
    const wxString fhn = ::wxGetFullHostName();
    if (fhn.empty()) return std::string();
#ifdef FFS_WIN
    return "Windows " + utf8CvrtTo<std::string>(fhn);
#elif defined FFS_LINUX
    return "Linux " + utf8CvrtTo<std::string>(fhn);
#endif
}


struct LockInformation
{
    LockInformation()
    {
        lockId = zen::generateGUID();
#ifdef FFS_WIN
        procDescr.processId = ::GetCurrentProcessId();
#elif defined FFS_LINUX
        procDescr.processId = ::getpid();
#endif
        procDescr.computerId = getComputerId();
    }

    LockInformation(wxInputStream& stream) //read
    {
        char formatDescr[sizeof(LOCK_FORMAT_DESCR)] = {};
        stream.Read(formatDescr, sizeof(LOCK_FORMAT_DESCR));         //file format header
        const int lockFileVersion = readPOD<boost::int32_t>(stream); //
        (void)lockFileVersion;

        //some format checking here?

        lockId = readString(stream);
        procDescr.processId  = static_cast<ProcessId>(readPOD<std::uint64_t>(stream)); //possible loss of precision (32/64 bit process) covered by buildId
        procDescr.computerId = readString(stream);
    }

    void toStream(wxOutputStream& stream) const //write
    {
        assert_static(sizeof(ProcessId) <= sizeof(std::uint64_t)); //ensure portability

        stream.Write(LOCK_FORMAT_DESCR, sizeof(LOCK_FORMAT_DESCR));
        writePOD<boost::int32_t>(stream, LOCK_FORMAT_VER);

        writeString(stream, lockId);
        writePOD<std::uint64_t>(stream, procDescr.processId);
        writeString(stream, procDescr.computerId);
    }

#ifdef FFS_WIN
    typedef DWORD ProcessId; //same size on 32 and 64 bit windows!
#elif defined FFS_LINUX
    typedef pid_t ProcessId;
#endif

    std::string lockId; //16 byte UUID

    struct ProcessDescription
    {
        ProcessId processId;
        std::string computerId;
    } procDescr;
};


//true: process not available, false: cannot say anything
enum ProcessStatus
{
    PROC_STATUS_NOT_RUNNING,
    PROC_STATUS_RUNNING,
    PROC_STATUS_ITS_US,
    PROC_STATUS_NO_IDEA
};
ProcessStatus getProcessStatus(const LockInformation::ProcessDescription& procDescr)
{
    if (procDescr.computerId != getComputerId() ||
        procDescr.computerId.empty()) //both names are empty
        return PROC_STATUS_NO_IDEA; //lock owned by different computer

#ifdef FFS_WIN
    if (procDescr.processId == ::GetCurrentProcessId()) //may seem obscure, but it's possible: a lock file is "stolen" and put back while the program is running
        return PROC_STATUS_ITS_US;

    //note: ::OpenProcess() is no option as it may successfully return for crashed processes!
    HANDLE snapshot = ::CreateToolhelp32Snapshot(
                          TH32CS_SNAPPROCESS, //__in  DWORD dwFlags,
                          0);                 //__in  DWORD th32ProcessID
    if (snapshot == INVALID_HANDLE_VALUE)
        return PROC_STATUS_NO_IDEA;
    ZEN_ON_BLOCK_EXIT(::CloseHandle(snapshot));

    PROCESSENTRY32 processEntry = {};
    processEntry.dwSize = sizeof(processEntry);

    if (!::Process32First(snapshot,       //__in     HANDLE hSnapshot,
                          &processEntry)) //__inout  LPPROCESSENTRY32 lppe
        return PROC_STATUS_NO_IDEA;
    do
    {
        if (processEntry.th32ProcessID == procDescr.processId)
            return PROC_STATUS_RUNNING; //process still running
    }
    while (::Process32Next(snapshot, &processEntry));

    return PROC_STATUS_NOT_RUNNING;

#elif defined FFS_LINUX
    if (procDescr.processId == ::getpid()) //may seem obscure, but it's possible: a lock file is "stolen" and put back while the program is running
        return PROC_STATUS_ITS_US;

    if (procDescr.processId <= 0 || procDescr.processId >= 65536)
        return PROC_STATUS_NO_IDEA; //invalid process id

    return zen::dirExists(Zstr("/proc/") + zen::toString<Zstring>(procDescr.processId)) ? PROC_STATUS_RUNNING : PROC_STATUS_NOT_RUNNING;
#endif
}


void writeLockInfo(const Zstring& lockfilename) //throw FileError
{
    //write GUID at the beginning of the file: this ID is a universal identifier for this lock (no matter what the path is, considering symlinks, distributed network, etc.)
    FileOutputStream lockFile(lockfilename); //throw FileError
    LockInformation().toStream(lockFile);
}


LockInformation retrieveLockInfo(const Zstring& lockfilename) //throw FileError, ErrorNotExisting
{
    //read GUID from beginning of file
    FileInputStream lockFile(lockfilename); //throw FileError, ErrorNotExisting
    return LockInformation(lockFile);
}


std::string retrieveLockId(const Zstring& lockfilename) //throw FileError, ErrorNotExisting
{
    return retrieveLockInfo(lockfilename).lockId;
}
}


void waitOnDirLock(const Zstring& lockfilename, DirLockCallback* callback) //throw FileError
{
    const std::wstring infoMsg = replaceCpy(_("Waiting while directory is locked (%x)..."), L"%x", std::wstring(L"\"") + lockfilename + L"\"");

    if (callback)
        callback->reportInfo(infoMsg);
    //---------------------------------------------------------------
    try
    {
        const LockInformation lockInfo = retrieveLockInfo(lockfilename); //throw FileError, ErrorNotExisting

        bool lockOwnderDead = false; //convenience optimization: if we know the owning process crashed, we needn't wait DETECT_EXITUS_INTERVAL sec
        switch (getProcessStatus(lockInfo.procDescr))
        {
            case PROC_STATUS_ITS_US: //since we've already passed LockAdmin, the lock file seems abandoned ("stolen"?) although it's from this process
            case PROC_STATUS_NOT_RUNNING:
                lockOwnderDead = true;
                break;
            case PROC_STATUS_RUNNING:
            case PROC_STATUS_NO_IDEA:
                break;
        }

        zen::UInt64 fileSizeOld;
        wxLongLong lockSilentStart = wxGetLocalTimeMillis();

        while (true)
        {
            const zen::UInt64 fileSizeNew = ::getLockFileSize(lockfilename); //throw FileError, ErrorNotExisting
            wxLongLong currentTime = wxGetLocalTimeMillis();

            if (fileSizeNew != fileSizeOld)
            {
                //received life sign from lock
                fileSizeOld     = fileSizeNew;
                lockSilentStart = currentTime;
            }

            if (lockOwnderDead || //no need to wait any longer...
                currentTime - lockSilentStart > DETECT_EXITUS_INTERVAL)
            {
                DirLock dummy(deleteAbandonedLockName(lockfilename), callback); //throw FileError

                //now that the lock is in place check existence again: meanwhile another process may have deleted and created a new lock!

                if (retrieveLockId(lockfilename) != lockInfo.lockId) //throw FileError, ErrorNotExisting
                    return; //another process has placed a new lock, leave scope: the wait for the old lock is technically over...

                if (getLockFileSize(lockfilename) != fileSizeOld) //throw FileError, ErrorNotExisting
                    continue; //belated lifesign

                removeFile(lockfilename); //throw FileError
                return;
            }

            //wait some time...
            const size_t GUI_CALLBACK_INTERVAL = 100;
            for (size_t i = 0; i < POLL_LIFE_SIGN_INTERVAL / GUI_CALLBACK_INTERVAL; ++i)
            {
                if (callback) callback->requestUiRefresh();
                wxMilliSleep(GUI_CALLBACK_INTERVAL);

                //show some countdown on abandoned locks
                if (callback)
                {
                    if (currentTime - lockSilentStart > EMIT_LIFE_SIGN_INTERVAL) //one signal missed: it's likely this is an abandoned lock:
                    {
                        long remainingSeconds = ((DETECT_EXITUS_INTERVAL - (wxGetLocalTimeMillis() - lockSilentStart)) / 1000).ToLong();
                        remainingSeconds = std::max(0L, remainingSeconds);

                        const std::wstring remSecMsg = replaceCpy(_P("1 sec", "%x sec", remainingSeconds), L"%x", toString<std::wstring>(remainingSeconds));

                        callback->reportInfo(infoMsg + L" " + remSecMsg);
                    }
                    else
                        callback->reportInfo(infoMsg); //emit a message in any case (might clear other one)
                }
            }
        }
    }
    catch (const ErrorNotExisting&)
    {
        return; //what we are waiting for...
    }
}


void releaseLock(const Zstring& lockfilename) //throw ()
{
    try
    {
        removeFile(lockfilename);
    }
    catch (...) {}
}


bool tryLock(const Zstring& lockfilename) //throw FileError
{
#ifdef FFS_WIN
    const HANDLE fileHandle = ::CreateFile(applyLongPathPrefix(lockfilename).c_str(),
                                           GENERIC_READ | GENERIC_WRITE, //use both when writing over network, see comment in file_io.cpp
                                           FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE,
                                           NULL,
                                           CREATE_NEW,
                                           FILE_ATTRIBUTE_NORMAL,
                                           NULL);
    if (fileHandle == INVALID_HANDLE_VALUE)
    {
#ifndef _MSC_VER
#warning fix this problem!
        //read-only FTP may return: ERROR_FILE_EXISTS (NetDrive @ GNU)
#endif
        if (::GetLastError() == ERROR_FILE_EXISTS)
            return false;
        else
            throw FileError(_("Error setting directory lock:") + L"\n\"" + lockfilename + L"\"" + L"\n\n" + getLastErrorFormatted());
    }
    ::CloseHandle(fileHandle);

#elif defined FFS_LINUX
    //O_EXCL contains a race condition on NFS file systems: http://linux.die.net/man/2/open
    ::umask(0); //important!
    const int fileHandle = ::open(lockfilename.c_str(), O_CREAT | O_WRONLY | O_EXCL, S_IRWXU | S_IRWXG | S_IRWXO);
    if (fileHandle == -1)
    {
        if (errno == EEXIST)
            return false;
        else
            throw FileError(_("Error setting directory lock:") + L"\n\"" + lockfilename + L"\"" + L"\n\n" + getLastErrorFormatted());
    }
    ::close(fileHandle);
#endif

    ScopeGuard guardLockFile = zen::makeGuard([&] { zen::removeFile(lockfilename); });

    //write UUID at the beginning of the file: this ID is a universal identifier for this lock (no matter what the path is, considering symlinks, etc.)
    writeLockInfo(lockfilename); //throw FileError

    guardLockFile.dismiss(); //lockfile created successfully
    return true;
}
}


class DirLock::SharedDirLock
{
public:
    SharedDirLock(const Zstring& lockfilename, DirLockCallback* callback = NULL) : //throw FileError
        lockfilename_(lockfilename)
    {
        while (!::tryLock(lockfilename))             //throw FileError
            ::waitOnDirLock(lockfilename, callback); //

        threadObj = boost::thread(LifeSigns(lockfilename));
    }

    ~SharedDirLock()
    {
        threadObj.interrupt(); //thread lifetime is subset of this instances's life
        threadObj.join();

        ::releaseLock(lockfilename_); //throw ()
    }

private:
    SharedDirLock(const DirLock&);
    SharedDirLock& operator=(const DirLock&);

    const Zstring lockfilename_;

    boost::thread threadObj;
};


class DirLock::LockAdmin //administrate all locks held by this process to avoid deadlock by recursion
{
public:
    static LockAdmin& instance()
    {
        static LockAdmin inst;
        return inst;
    }

    //create or retrieve a SharedDirLock
    std::shared_ptr<SharedDirLock> retrieve(const Zstring& lockfilename, DirLockCallback* callback) //throw FileError
    {
        //optimization: check if there is an active(!) lock for "lockfilename"
        FileToUuidMap::const_iterator iterUuid = fileToUuid.find(lockfilename);
        if (iterUuid != fileToUuid.end())
        {
            const std::shared_ptr<SharedDirLock>& activeLock = findActive(iterUuid->second); //returns null-lock if not found
            if (activeLock)
                return activeLock; //SharedDirLock is still active -> enlarge circle of shared ownership
        }

        try //actual check based on lock UUID, deadlock prevention: "lockfilename" may be an alternative name for an already active lock
        {
            const std::string lockId = retrieveLockId(lockfilename); //throw FileError, ErrorNotExisting

            const std::shared_ptr<SharedDirLock>& activeLock = findActive(lockId); //returns null-lock if not found
            if (activeLock)
            {
                fileToUuid[lockfilename] = lockId; //perf-optimization: update relation
                return activeLock;
            }
        }
        catch (...) {} //catch everything, let SharedDirLock constructor deal with errors, e.g. 0-sized/corrupted lock file

        //not yet in buffer, so create a new directory lock
        std::shared_ptr<SharedDirLock> newLock(new SharedDirLock(lockfilename, callback)); //throw FileError
        const std::string newLockId = retrieveLockId(lockfilename); //throw FileError, ErrorNotExisting

        //update registry
        fileToUuid[lockfilename] = newLockId; //throw()
        uuidToLock[newLockId]    = newLock;   //

        return newLock;
    }

private:
    LockAdmin() {}

    std::shared_ptr<SharedDirLock> findActive(const std::string& lockId) //returns null-lock if not found
    {
        UuidToLockMap::const_iterator iterLock = uuidToLock.find(lockId);
        return iterLock != uuidToLock.end() ?
               iterLock->second.lock() : nullptr; //try to get shared_ptr; throw()
    }

    typedef std::weak_ptr<SharedDirLock> SharedLock;

    typedef std::string UniqueId;
    typedef std::map<Zstring, UniqueId, LessFilename> FileToUuidMap; //n:1 handle uppper/lower case correctly
    typedef std::map<UniqueId, SharedLock>            UuidToLockMap; //1:1

    FileToUuidMap fileToUuid; //lockname |-> UUID; locks can be referenced by a lockfilename or alternatively a UUID
    UuidToLockMap uuidToLock; //UUID |-> "shared lock ownership"
};


DirLock::DirLock(const Zstring& lockfilename, DirLockCallback* callback) //throw FileError
{
#ifdef FFS_WIN
    const DWORD bufferSize = std::max(lockfilename.size(), static_cast<size_t>(10000));
    std::vector<wchar_t> volName(bufferSize);
    if (::GetVolumePathName(lockfilename.c_str(), //__in   LPCTSTR lpszFileName,
                            &volName[0],          //__out  LPTSTR lpszVolumePathName,
                            bufferSize))          //__in   DWORD cchBufferLength
    {
        DWORD dt = ::GetDriveType(&volName[0]);
        if (dt == DRIVE_CDROM)
            return; //we don't need a lock for a CD ROM
    }
#endif

    sharedLock = LockAdmin::instance().retrieve(lockfilename, callback);
}