NCBI C++ ToolKit

PInterProcessLock – Helper functor for CGuard<> to e.g. help specify the waiting timeout.

CInterProcessLock ipl("MyLock"); CInterProcessLock_Guard ipl_guard (ipl, PInterProcessLock(3.456, 0.333));

/* $Id: interprocess_lock.hpp 84598 2018-11-20 20:23:54Z ucko $
* ===========================================================================
* National Center for Biotechnology Information
* This software/database is a "United States Government Work" under the
* terms of the United States Copyright Act. It was written as part of
* the author's official duties as a United States Government employee and
* thus cannot be copyrighted. This software/database is freely available
* to the public for use. The National Library of Medicine and the U.S.
* Government have not placed any restriction on its use or reproduction.
* Although all reasonable efforts have been taken to ensure the accuracy
* and reliability of the software and data, the NLM and the U.S.
* Government do not and cannot warrant the performance or results that
* may be obtained by using this software or data. The NLM and the U.S.
* Government disclaim all warranties, express or implied, including
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* Please cite the author in any work or product based on this material.
* ===========================================================================
* Authors: Vladimir Ivanov, Denis Vakatov
/// @file interprocess_lock.hpp
/// Simple inter-process lock.
/// Defines classes:
/// CInterProcessLock
/// PInterProcessLock
/// CInterProcessLockException
#if !defined(NCBI_OS_MSWIN) && !defined(NCBI_OS_UNIX)
# error "CInterProcessLock is not implemented on this platform"
/** @addtogroup Process
* @{
/// CInterProcessLock --
/// Simple inter-process lock.
/// When the process terminates (normally or otherwise) all locks will be
/// removed automaticaly. On Unix, the lock file can be left in the
/// filesystem, but the lock itself will be removed anyway and the lock file
/// can be reused.
/// Please consider to use class CGuard<> for locking resources in
/// an exception-safe manner. See also CInterProcessLock_Guard to help specify
/// timeouts for the locking operation when using CGuard<>.
/// The lock can be safely acquired from different threads (and, with all
/// timeouts observed).
/// @param name
/// Name of the lock.
/// The name must be a Unix-path like, and its length must not
/// exceed the maximum path length that is specific for the OS where the
/// application runs.
/// @note
/// This constructor will not try to acquire a lock on creation.
/// @note
/// - On Unix, if a pathless file name is given, then the corresponding
/// file will be created in a well-known system-specific location
/// (usually as '/var/tmp/<name>'); if the name represents an absolute
/// file path, then the exact path will be used to create the lock file.
/// - On Windows, no actual files will be created at the specified path.
/// @attention
/// - Relative paths are not allowed (regardless of the OS).
/// - Empty name is not allowed.
/// - Locking may not work for the files located on network filesystems
/// (like NFS).
/// @sa Lock, TryLock, GetName
CInterProcessLock(const string& name);
/// Call Unlock()
/// @name
/// Lock/guard interface (to use with CGuard<> or CInterProcessLock_Guard)
/// @{
/// Try to acquire the lock.
/// On any error, or if the lock is already held by another process and
/// it could not be acquired within the allotted time period,
/// throw CInterProcessLockException.
/// @param timeout
/// How much time Lock() should wait before giving up (with error).
/// Default timeout value is interpreted as infinite.
/// @param granularity
/// On the systems (such as Unix) where there is no support for waiting
/// for the lock with a timeout, the waiting is implemented using a
/// loop of "try to lock" calls. This parameter specifies how much time to
/// wait between these calls. It will be auto-limited to the closest
/// whole delimiter of the 'timeout' value (and it will never exceed it).
/// Default or infinite granularity timeout is converted into:
/// MIN(timeout/5, 0.5sec).
/// @note
/// If 'timeout' is passed infinite, then the 'granularity' parameter
/// actually will not be used at all -- both on Windows and on Unix -- as
/// they both support a "honest" infinite waiting.
/// @note
/// One process can acquire the lock more than once -- but it need
/// to use the same CInterProcessLock object for Lock(), and then it will
/// need to call Unlock() as many times in order to release the lock for
/// other processes.
/// @note
/// If the lock object (such as file on UNIX or system mutex on Windows)
/// doesn't exist it will be created.
/// @sa TryLock, SetLockTimeout
void Lock(const CTimeout& timeout = CTimeout(CTimeout::eInfinite),
const CTimeout& granularity = CTimeout(CTimeout::eInfinite));
/// Release the lock.
/// On any error (including when the lock is not held by the process),
/// throw CInterProcessLockException.
/// @sa Lock, TryLock, Remove
void Unlock(void);
/// @}
/// Try to acquire the lock.
/// Acquire the lock if it can be done right away. Return immediately.
/// @return
/// - TRUE, if the lock has been successfully acquired.
/// - FALSE, if the lock is already held by another process
/// or if any error occurs.
/// @sa Lock
bool TryLock(void);
/// Call Unlock() and removes lock object from the system.
/// On Unix, the Unlock() method do not remove used lock file from
/// the system, it just release a lock. If you don't need this file
/// anymore, use this method to remove it. We cannot remove it
/// automaticaly in the Unlock(), because on Unix locking/unlocking
/// is not an atomic operations and race condition is possible if
/// at time of deleting some other process wait to acquire a lock
/// using the same lock file.
/// @note
/// On Windows, it works almost as Unlock().
/// @sa Unlock
void Remove(void);
/// Get the original name of the lock -- exactly as it was specified
/// in the constructor
const string& GetName(void) const { return m_Name; }
/// Get the internal name of the lock -- as it is being used in the calls
/// to the OS (such as '/var/tmp/<name>' rather than just '<name>' on UNIX)
const string& GetSystemName(void) const { return m_SystemName; }
/// Original name of the lock
string m_Name;
/// Adjusted name of the lock
string m_SystemName;
/// OS-specific lock handle
#if defined(NCBI_OS_UNIX)
typedef int TLockHandle;
#elif defined(NCBI_OS_MSWIN)
typedef HANDLE TLockHandle;
TLockHandle m_Handle;
/// PInterProcessLock --
/// Helper functor for CGuard<> to e.g. help specify the waiting timeout.
/// @example
/// CInterProcessLock ipl("MyLock");
/// CInterProcessLock_Guard ipl_guard
/// (ipl,
/// PInterProcessLock(3.456, 0.333));
PInterProcessLock(const CTimeout& timeout,
const CTimeout& granularity = CTimeout(CTimeout::eInfinite))
: m_Timeout(timeout),
void operator()(resource_type& resource) const
resource.Lock(m_Timeout, m_Granularity);
/// Convenience typedef for PInterProcessLock
/// @sa PInterProcessLock
/// CInterProcessLockException --
/// Error types that file operations can generate.
enum EErrCode {
eLockTimeout, ///< The lock could not be acquired in the time allotted
eNameError, ///< Incorrect name for a lock
eCreateError, ///< Cannot create the lock object in the OS
eLockError, ///< Cannot acquire a lock (not eLockTimeout, eCreateError)
eUnlockError, ///< Cannot release the lock
eMultipleLocks, ///< Attempt to lock already locked object in the same process
eNotLocked ///< Attempt to unlock a not-yet-acquired lock
/// Translate from an error code value to its string representation.
virtual const char* GetErrCodeString(void) const override;
// Standard exception boilerplate code.
/* @} */
CCoreException –.
Definition: ncbiexpt.hpp:1476
CInterProcessLockException –.
CInterProcessLock –.
CTimeout – Timeout interval.
Definition: ncbitime.hpp:1693
#define NCBI_EXCEPTION_DEFAULT(exception_class, base_class)
To help declare new exception class.
Definition: ncbiexpt.hpp:1315
PInterProcessLock(const CTimeout &timeout, const CTimeout &granularity=CTimeout(CTimeout::eInfinite))
CGuard< CInterProcessLock, PInterProcessLock > CInterProcessLock_Guard
Convenience typedef for PInterProcessLock.
CInterProcessLock resource_type
void operator()(resource_type &resource) const
End previously defined NCBI scope.
Definition: ncbistl.hpp:103
Define ncbi namespace.
Definition: ncbistl.hpp:100
@ eInfinite
Infinite timeout.
Definition: ncbitime.hpp:1699
Definition: ncbi_export.h:1283
#define HANDLE
An abstraction for a file handle.
Definition: mdb.c:383
Defines: CTimeFormat - storage class for time format.
Modified on Wed Apr 24 14:13:15 2024 by rev. 669887