Product Documentation

FairCom ISAM for C

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Complications with ctLOCK_TOP

Extended locking, the standard locking method for non-Unix systems in the FairCom DB Standalone Multi-user model, uses ctLOCK_TOP to determine the highest potential offset within a file.

Note: Extended locking will only work if all applications sharing files use the same offset, otherwise locks will not be properly implemented.

ctLOCK_TOP is not an issue with any of the FairCom DB client/server models, which automatically handle locking for any type of FairCom DB client.

When mixing platforms in the Standalone Multi-user model, ensure the ctLOCK_TOP define is consistent between different platforms. Use the lowest common setting to maintain compatibility. For example, when mixing 16-bit and 32-bit applications, use 0x7fffffff. The default settings for Standard libraries are:


ctLOCK_TOP value


(ULONG) 0xffffffff


(ULONG) 0x4fffffff


Not implemented

When using FairCom DB Professional with ctHUGEFILE defined, there are additional limitations.