MFS and READNEXT [Revelation On-Line Wiki]

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====== MFS and READNEXT ======

One reason an MFS may wish to trap the READNEXT call is in order to fulfill READNEXT calls without recourse to the BFS. In OpenInsight, both [[system_mfss_in_openinsight|QUICKDEX.MFS]] and [[system_mfss_in_openinsight|SI.MFS]] trap the READNEXT call, returning record keys without passing the call to the BFS.

[[system_mfss_in_openinsight|QUICKDEX.MFS]] provides a good model for using an MFS to trap READNEXT requests. If the filing system SELECT call has returned a select mode of 1 (latent file select), [[system_mfss_in_openinsight|QUICKDEX.MFS]] traps the READNEXT call. The MFS reads the %RECORDS% record from the current file, and returns it as the next block of keys. If another READNEXT call comes down to the MFS, [[system_mfss_in_openinsight|QUICKDEX.MFS]] simply returns a false, since all keys were returned in the first call.