A general file locking class. More...
#include <FileLock.h>
Public Member Functions | |
| FileLock (const std::string &filename, unsigned int timeout=DEFAULT_LOCK_TIMEOUT, bool use_pid=true) | |
| bool | acquire (bool &lock_removed) |
| bool | acquire () |
| bool | release (bool force=false) |
| int | check (bool log_error=true) |
Static Public Member Functions | |
| static std::string | getLockSuffix () |
Static Public Attributes | |
| static const int | DEFAULT_LOCK_TIMEOUT |
| static const std::string | LOCK_SUFFIX |
A general file locking class.
This class can be used when protected access is required to files which are used by multiple processes or threads. Call acquire() to obtain a lock and release() to release it when finished. check() can be used to verify if a lock is valid for the current process. Locks are independent of FileLock objects - locks are only created and destroyed through acquire() and release(), not on creation or destruction of FileLock objects.
Unless use_pid is set false, the process ID and hostname of the calling process are stored in a file filename.lock in the form pid. This information is used to determine whether a lock is still valid. It is also possible to specify a timeout on the lock.
To ensure an atomic locking operation, acquire() first creates a temporary lock file filename.lock.XXXXXX, then attempts to rename this file to filename.lock. After a successful rename the lock file is checked to make sure the correct process ID and hostname are inside. This eliminates race conditions where multiple processes compete to obtain the lock.
| Arc::FileLock::FileLock | ( | const std::string & | filename, | |
| unsigned int | timeout = DEFAULT_LOCK_TIMEOUT, |
|||
| bool | use_pid = true | |||
| ) |
Create a new FileLock object.
| filename | The name of the file to be locked | |
| timeout | The timeout of the lock | |
| use_pid | If true, use process id in the lock and to determine lock validity |
| bool Arc::FileLock::acquire | ( | ) |
Acquire the lock.
Callers can use this version of acquire() if they do not care whether an invalid lock was removed in the process of obtaining the lock.
| bool Arc::FileLock::acquire | ( | bool & | lock_removed | ) |
Acquire the lock.
Returns true if the lock was acquired successfully. Locks are acquired if no lock file currently exists, or if the current lock file is invalid. A lock is invalid if the process ID inside the lock no longer exists on the host inside the lock, or the age of the lock file is greater than the lock timeout.
| lock_removed | Set to true if an existing lock was removed due to being invalid. In this case the caller may decide to check or delete the file as it is potentially corrupted. |
| int Arc::FileLock::check | ( | bool | log_error = true |
) |
Check the lock is valid.
Returns 0 if the lock is valid for the current process, the pid inside the lock if the lock is owned by another process on the same host, and -1 if the lock is owned by another host or any other error occurred. log_error may be set to false to log error messages at INFO level, in cases where the lock not existing or being owned by another host are not errors.
| bool Arc::FileLock::release | ( | bool | force = false |
) |
Release the lock.
| force | Remove the lock without checking ownership or timeout |
1.6.3