[Bug 6800] New: sem_post does not properly wake waiting thread

bugzilla at busybox.net bugzilla at busybox.net
Tue Jan 14 21:20:21 UTC 2014


           Summary: sem_post does not properly wake waiting thread
           Product: uClibc
           Version: 0.9.34
          Platform: All
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P5
         Component: Threads
        AssignedTo: unassigned at uclibc.org
        ReportedBy: bb at jeffhansen.com
                CC: uclibc-cvs at uclibc.org
   Estimated Hours: 0.0

Created attachment 5186
  --> https://bugs.busybox.net/attachment.cgi?id=5186
Proof of bug

In the attached example (without USE_FUTEX defined), the "^^ got in" text does
not ever print out as expected, on x86 and MIPS architectures.  This is very
problematic in applications post them immediately wait, where other threads
need to be allowed a sliver of time in between.

If you use raw Linux futex syscalls, Linux properly wakes up the last waiting
thread so that "^^ got in" prints out, as shown by defining the USE_FUTEX

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