void CInterProcessLock::Lock(const CTimeout& timeout,
const CTimeout& granularity)
{
CFastMutexGuard LOCK(s_ProcessLock);
// Check that lock with specified name not already locked
// in the current process.
TLocks::iterator it = s_Locks->find(m_SystemName);
if (m_Handle != kInvalidLockHandle) {
// The lock is already set in this CInterProcessLock object,
// just increase reference counter.
_VERIFY(it != s_Locks->end());
it->second++;
return;
} else {
if (it != s_Locks->end()) {
// The lock already exists in the current process.
// We can use one CInterProcessLock object with
// multiple Lock() calls, but not with different
// CInterProcessLock objects. For example, on MS-Windows,
// we cannot wait on the same mutex in the same thread.
// So, two different objects can set locks simultaneously.
// And for OS-compatibility we can do nothing here,
// except throwing an exception.
NCBI_THROW(CInterProcessLockException, eMultipleLocks,
"Attempt to lock already locked object " \
"in the same process");
}
}
// Try to acquire a lock with specified timeout
#if defined(NCBI_OS_UNIX)
// Open lock file
mode_t perm = CDirEntry::MakeModeT(
CDirEntry::fRead | CDirEntry::fWrite /* user */,
CDirEntry::fRead | CDirEntry::fWrite /* group */,
0, 0 /* other & special */);
int fd = open(m_SystemName.c_str(), O_CREAT | O_RDWR, perm);
if (fd == -1) {
NCBI_THROW(CInterProcessLockException, eCreateError,
string("Error creating lockfile ") + m_SystemName +
": " + strerror(errno));
}
// Try to acquire the lock
int x_errno = 0;
if (timeout.IsInfinite() || timeout.IsDefault()) {
while ((x_errno = s_UnixLock(fd))) {
if (errno != EAGAIN)
break;
}
} else {
unsigned long ms = timeout.GetAsMilliSeconds();
if ( !ms ) {
// Timeout == 0
x_errno = s_UnixLock(fd);
} else {
// Timeout > 0
unsigned long ms_gran;
if ( granularity.IsInfinite() ||
granularity.IsDefault() )
{
ms_gran = min(ms/5, (unsigned long)500);
} else {
ms_gran = granularity.GetAsMilliSeconds();
}
// Try to lock within specified timeout
for (;;) {
x_errno = s_UnixLock(fd);
if ( !x_errno ) {
// Successfully locked
break;
}
if (x_errno != EACCES &&
x_errno != EAGAIN ) {
// Error
break;
}
// Otherwise -- sleep granularity timeout
unsigned long ms_sleep = ms_gran;
if (ms_sleep > ms) {
ms_sleep = ms;
}
if ( !ms_sleep ) {
break;
}
SleepMilliSec(ms_sleep);
ms -= ms_sleep;
}
// Timeout
if ( !ms ) {
close(fd);
NCBI_THROW(CInterProcessLockException, eLockTimeout,
"The lock could not be acquired in the time " \
"allotted");
}
} // if (!ms)
} // if (timeout.IsInfinite())
// Error
if ( x_errno ) {
close(fd);
NCBI_THROW(CInterProcessLockException, eLockError,
"Error creating lock");
}
// Success
m_Handle = fd;
#elif defined(NCBI_OS_MSWIN)
HANDLE handle = ::CreateMutex(NULL, TRUE, _T_XCSTRING(m_SystemName));
errno_t errcode = ::GetLastError();
if (handle == kInvalidLockHandle) {
switch(errcode) {
case ERROR_ACCESS_DENIED:
// Mutex with specified name already exists,
// but we don't have enough rights to open it.
NCBI_THROW(CInterProcessLockException, eLockError,
"The lock already exists");
break;
case ERROR_INVALID_HANDLE:
// Some system object with the same name already exists
NCBI_THROW(CInterProcessLockException, eLockError,
"Error creating lock, system object with the same" \
"name already exists");
break;
default:
// Unknown error
NCBI_THROW(CInterProcessLockException, eCreateError,
"Error creating lock");
break;
}
} else {
// Mutex with specified name already exists
if (errcode == ERROR_ALREADY_EXISTS) {
// Wait
DWORD res;
if (timeout.IsInfinite() || timeout.IsDefault()) {
res = WaitForSingleObject(handle, INFINITE);
} else {
res = WaitForSingleObject(handle, timeout.GetAsMilliSeconds());
}
switch(res) {
case WAIT_OBJECT_0:
// The lock has been acquired
break;
case WAIT_TIMEOUT:
::CloseHandle(handle);
NCBI_THROW(CInterProcessLockException, eLockTimeout,
"The lock could not be acquired in the time " \
"allotted");
break;
case WAIT_ABANDONED:
// The lock is in abandoned state... Other thread/process
// owning it was terminated. We can reuse this mutex, but
// it is better to wait until it will be released by OS.
/* FALLTHRU */
default:
::CloseHandle(handle);
NCBI_THROW(CInterProcessLockException, eLockError,
"Error creating lock");
break;
}
}
m_Handle = handle;
}
#endif
// Set reference counter to 1
(*s_Locks)[m_SystemName] = 1;
}
