John Rocha created AMQCPP-498:
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Summary: Client doesn't work on Linux Red Hat 6.4 systems, fails
when setting thread priority
Key: AMQCPP-498
URL: https://issues.apache.org/jira/browse/AMQCPP-498
Project: ActiveMQ C++ Client
Issue Type: Bug
Components: Decaf
Affects Versions: 3.5.0
Environment: Linux Red Hat 6.4
Reporter: John Rocha
Assignee: Timothy Bish
Priority: Critical
Attachments: patch.TBD
Client doesn't work on Linux Red Hat 6.4 systems. It fails throwing the
exception {panel}Failed to set new Therad priority to value: 18{panel}
This is coming from the file
{{{color:brown}src/main/decaf/internal/util/concurrent/unix/PlatformThread.cpp{color}}}
when it's creating a new thread.
We encountered this problem when we started running our code on a new operating
system. It worked fine on Redhat 5.8 and SuSE SLES10, but then it started
failing on Redhat 6.4.
I did some digging and found a defect logged against the _+pthread+_ library
at: http://sourceware.org/bugzilla/show_bug.cgi?id=10828.
{panel}(This problem was found by analyzing a failure of LSB distribution
compliance test, lsb-runtime, v. 4.0.2.)
A relatively new change in $GITROOT/glibc/nptl/pthread_attr_setschedparam.c
(2009-04-23 according to git) adds a check to pthread_attr_setschedparam() call
whether the priority being set is compatible with the scheduling policy already
set in the structure; if the priority is not in the prescribed range, it fails,
generating the EINVAL error.
This check, although well intended, has a side effect that can break existing
code (at least the LSB tests): it makes the process of initializing a
pthread_attr structure order-dependent on Linux.
As Linux does not use the numeric priority for SCHED_OTHER, which is the
default, and sched_get_priority_min() and sched_priority_max() return 0.
Therefore:
If a programmer calls pthread_attr_init(), then pthread_attr_setschedpolicy()
to set SCHED_RR or SCHED_FIFO, and then pthread_attr_setschedparam(), it works.
But if the other way around (priority first, then scheduling policy), it fails
for "no apparent reason".{panel}
I did some debugging in the code and found that {{unix/PlatformThread.cpp}}'s
method {{createNewThread()}} sets the scheduling priority but doesn't set the
scheduling policy. And the default value for the scheduling policy is
SCHED_OTHER(0) which only supports a priority value of 0.
I have a proposed patch which:
# validates the return values of all pthread calls and
# only sets the priority iff the policy is sset to SCHED_FIFO or SCHED_RR
Granted, we never set the policy so one could argue that we should just remove
setting of the priority. However, I suspect that the true desire is to inherit
the current threads scheduling value and set the priority based on that. So I
anticipate tha future changes may actually set the policy. I didn't do this
though.
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