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Although libxcb can yield dramatic improvements in speed,
memory footprint, and responsiveness, and will probably
become the default Xlib for X.org/freedesktop.org, it is
still experimental software.  Some broken callers will abort()
on locking assertion failures.  As a temporary workaround, set
LIBXCB_ALLOW_SLOPPY_LOCK in your environment to skip the abort().
This may result in noisy stacktrace printing.
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