In short, yes. Sstate files are first written into a random temporary file, then renamed when writing is done. DL_DIR items are guarded by lock files (look for lockfile in bitbake/lib/bb/fetch2/__init__.py).
Clearing out old items from sstate and download caches must be done when no builds are running. Alex On Tue, 1 Aug 2023 at 15:26, Daniel Klauer <daniel.kla...@gin.de> wrote: > > Hi, > > Is it safe to share DL_DIR and SSTATE_DIR between multiple Yocto builds that > are running in parallel? Are all the accesses done by bitbake/Yocto atomic or > protected by locking? This came up because I'm wondering whether it would be > possible to safely share a single downloads mirror and sstate cache between > multiple build agents (and not just read-only over a HTTP server, but writing > too). > > The documentation contains some sentences like "You can safely share this > directory between multiple builds on the same development machine" and "You > can reuse the directory for multiple builds", but this does not seem to > clarify whether parallel builds are allowed. I have found an older message > [1], which suggests that SSTATE_DIR is safe to share, but that still leaves > me wondering about DL_DIR. Presumably bitbake uses plain rename()/mv for > tarballs, as for sstate, making them thread-safe. But what about Git repos - > it's clear that Git itself uses locking, but bitbake may do more than just > git operations. Does anyone have any more information on this, besides > digging into the bitbake and bbclass sources? Is it "thread-safe"? A > potentially related question: How does bitbake handle multiple do_fetch tasks > for the same repository running in parallel (if you have multiple recipes > using the same repo)? > > Thanks & kind regards, > Daniel > > [1] https://www.yoctoproject.org/pipermail/yocto/2016-November/032873.html > > >
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