• Jeffrey Lee's avatar
    [480] Make use of fsfile_ReadInfoNoLen · e2242870
    Jeffrey Lee authored
    Update EnsureCanonicalObject so that it can optionally skip reading the
    file/object length, based on the new argument R7. Then trace back
    through the callers to have them pass in an appropriate value based on
    whether they care about the length or not.
    TopPath_DoBusinessToPath has also gained a new flag bit to suppress
    reading the length, but so far I've only updated DoThePath to use it.
    Result: If you have a file in PipeFS which is open for writing, and then
    attempt to open it for reading using OS_Find, it'll now open immediately
    instead of PipeFS trying to block/sleep until it's no longer open for
    Why: Since at least as far back as RISC OS 3.6, PipeFS tries to sleep
    inside fsfile_ReadInfo if the file is open for writing. But a
    combination of buggy sleep logic and TaskWindow's lazy approach to
    UpCall 6 meant that (prior to TaskWindow 0.65) it wouldn't sleep for
    long and would instead allow the open to proceed while the file is still
    open for write. The ability to have both a reader & writer active at the
    same time is basically the whole point of PipeFS, so this change
    restores that pre-TaskWindow 0.65 behaviour without having to remove the
    sleep logic from PipeFS (it's a well-intentioned feature, even though
    it's been broken for decades)
    Tested by performing a ROM build, checking that it works, and running
    some PipeFS tests.
    This fixes the original issue described in ticket 480:
    Version 2.90. Tagged as 'FileSwitch-2_90'
Canonical 38 KB