This page serves for managing parameters of realization of shared access of several users to GDB and shared library. The page is shown at figure 8-7.
Figure 8-7. “ObjectLand settings” property sheet, page “Shared access”
To provide correctness of making changes to the databases with simultaneous work of several users, ObjectLand uses the mechanism of temporary locking the access to the data in files for the time (usually short) while one user performs operations with this data. It means the following: when one user performs the operation changing the data in GDB or shared library files, first of all the system sets exclusive locking for the appropriate files and only after that writes data into the file. After completing the operation the locking is released. If the performed operation requires only reading from the file, shared locking is set for this time.
Data about locking set for the present moment by all work sessions is recorded into the locking file which is located in GDB folder (or in the shared library folder accordingly).
In case if during the locking period another user tries to perform an operation requiring reading or writing data, the system attempts to set locking of the corresponding type again. It becomes possible only for two shared lockings, that is, for simultaneous reading of data. Otherwise, (that is, when at least one locking is exclusive) before setting the next locking the system awaits when the current locking will be released. Parameter Lock timeout determines the time on expiration of which the system displays a message about the impossibility to perform the operation and in some cases offers to repeat the attempt.
For displaying the current status of shared work sessions in the navigation window the system performs a regular session scan. Parameter Period of request about sessions assigns the time between two successive session scans. If the scanned session does not respond during the time assigned by the parameter Timeout of request about sessions, the system displays a warning message.
All named parameters are determined separately for access to GDB and to the shared library.
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