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This tries to convince Coverity that we don't have a resource leak:
CID 1438157: (RESOURCE_LEAK)
Handle variable "monitor_fd" going out of scope leaks the handle.
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Volker Lendecke <vl@samba.org>
Otherwise Coverity reports this:
CID 1438160: (CHECKED_RETURN)
Calling "poll(NULL, 0UL, 1)" without checking return value. This
library function may fail and return an error code.
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Volker Lendecke <vl@samba.org>
In pthreadpool_tevent_job_send() we remember if the job will be chdir
safe. It means we means we need to ask the callers pool when calling
pthreadpool_tevent_per_thread_cwd(), as the callers pool might
be a wrapper using pthreadpool_tevent_force_per_thread_cwd().
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
Reported-by: David Disseldorp <ddiss@samba.org>
Signed-off-by: Ralph Boehme <slow@samba.org>
Reviewed-by: David Disseldorp <ddiss@samba.org>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
Pair-Programmed-With: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
This can be used implement a generic per thread impersonation
for thread pools.
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
This makes it possible to monitor the pthreadpool for exited worker
threads and may restart new threads from the main thread again.
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
Note this currently this doesn't enforce the support for
unshare(CLONE_FS) as some contraint container environment
(e.g. docker) reject the whole unshare() system call.
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
This can be used to check if worker threads run with
unshare(CLONE_FS).
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
This paves the way for pthreadpool jobs that are path based.
Callers can use pthreadpool_per_thread_cwd() to check if
the current pool supports it.
Pair-Programmed-With: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Ralph Boehme <slow@samba.org>
Pair-Programmed-With: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Ralph Boehme <slow@samba.org>
Signed-off-by: Stefan Metzmacher <metze@samba.org>
This seems to be a really rare race, it's likely that the immediate
event will still trigger and cleanup.
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
We should avoid traversing a linked list within a thread without holding
a mutex!
Using a mutex would be very tricky as we'll likely deadlock with
the mutexes at the raw pthreadpool layer.
So we use somekind of spinlock using atomic_thread_fence in order to
protect the access to job->state->glue->{tctx,ev} in
pthreadpool_tevent_job_signal().
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
This avoids the expected helgrind/drd warnings on the job states which
are protected by the thread fence.
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
In the direction from the main process to the job thread, we have:
- 'maycancel', which is set when tevent_req_cancel() is called,
- 'orphaned' is the job request, tevent_context or pthreadpool_tevent
was talloc_free'ed.
The job function can consume these by using:
/*
* return true - if tevent_req_cancel() was called.
*/
bool pthreadpool_tevent_current_job_canceled(void);
/*
* return true - if talloc_free() was called on the job request,
* tevent_context or pthreadpool_tevent.
*/
bool pthreadpool_tevent_current_job_orphaned(void);
/*
* return true if canceled and orphaned are both false.
*/
bool pthreadpool_tevent_current_job_continue(void);
In the other direction we remember the following points
in the job execution:
- 'started' - set when the job is picked up by a worker thread
- 'executed' - set once the job function returned.
- 'finished' - set when pthreadpool_tevent_job_signal() is entered
- 'dropped' - set when pthreadpool_tevent_job_signal() leaves with orphaned
- 'signaled' - set when pthreadpool_tevent_job_signal() leaves normal
There're only one side writing each element,
either the main process or the job thread.
This means we can do the coordination with a full memory
barrier using atomic_thread_fence(memory_order_seq_cst).
lib/replace provides fallbacks if C11 stdatomic.h is not available.
A real pthreadpool requires pthread and atomic_thread_fence() (or an
replacement) to be available, otherwise we only have pthreadpool_sync.c.
But this should not make a real difference, as at least
__sync_synchronize() is availabe since 2005 in gcc.
We also require __thread which is available since 2002.
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
This means it will go aways together with glue and thte event context.
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
Autobuild-User(master): Stefan Metzmacher <metze@samba.org>
Autobuild-Date(master): Thu Jul 12 17:18:01 CEST 2018 on sn-devel-144
Instead of leaking the memory forever, we retry the cleanup,
if other pthreadpool_tevent_*() functions are used.
pthreadpool_tevent_cleanup_orphaned_jobs() could also be called
by external callers.
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
This makes it much easier to handle orphaned jobs,
we either wait for the immediate tevent to trigger
or we just keep leaking the memory.
The next commits will improve this further.
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
This can be used in combination with pthreadpool_cancel_job() to
implement a multi step shutdown of the pool.
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
These can be used to implement some kind of flow control in the caller.
E.g. unless pthreadpool_tevent_queued_jobs() is lower than
pthreadpool_tevent_max_threads() is good to prepare new jobs.
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
These can be used to implement some kind of flow control in the caller.
E.g. unless pthreadpool_queued_jobs() is lower than
pthreadpool_max_threads() is good to prepare new jobs.
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
We need to pthread_mutex_lock/unlock the pool mutex
before we can destroy it.
The following test would trigger this.
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
Otherwise it's an error if not at least one thread is possible.
This gives a much saner behaviour and doesn't end up with
unexpected sync processing.
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
This makes further restructuring easier to implement and understand.
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
Currently 0 also means unlimited, but that will change soon,
to force no thread and strict sync processing.
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>
Christof's idea from
https://lists.samba.org/archive/samba-technical/2017-December/124384.html
was that the thread already exited. It could also be that the thread is
not yet idle when the new pthreadpool_add_jobs comes around the corner.
Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Christof Schmitt <cs@samba.org>
Autobuild-User(master): Christof Schmitt <cs@samba.org>
Autobuild-Date(master): Wed Dec 13 04:46:12 CET 2017 on sn-devel-144
Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
Autobuild-User(master): Jeremy Allison <jra@samba.org>
Autobuild-Date(master): Wed Dec 13 00:44:57 CET 2017 on sn-devel-144
After the race is before the race:
1) Create an idle thread
2) Add a job: This won't create a thread anymore
3) Immediately fork
The idle thread will be woken twice before it's actually woken up: Both
pthreadpool_add_job and pthreadpool_prepare_pool call cond_signal, for
different reasons. We must look at pool->prefork_cond first because otherwise
we will end up in a blocking job deep within a fork call, the helper thread
must take its fingers off the condvar as quickly as possible. This means that
after the fork there's no idle thread around anymore that would pick up the job
submitted in 2). So we must keep the idle threads around across the fork.
The quick solution to re-create one helper thread in pthreadpool_parent has a
fatal flaw: What do we do if that pthread_create call fails? We're deep in an
application calling fork(), and doing fancy signalling from there is really
something we must avoid.
This has one potential performance issue: If we have hundreds of idle threads
(do we ever have that) during the fork, the call to pthread_mutex_lock on the
fork_mutex from pthreadpool_server (the helper thread) will probably cause a
thundering herd when the _parent call unlocks the fork_mutex. The solution for
this to just keep one idle thread around. But this adds code that is not
strictly required functionally for now.
More detailed explanation from Jeremy:
First, understanding the problem the test reproduces:
add a job (num_jobs = 1) -> creates thread to run it.
job finishes, thread sticks around (num_idle = 1).
num_jobs is now zero (initial job finished).
a) Idle thread is now waiting on pool->condvar inside
pthreadpool_server() in pthread_cond_timedwait().
Now, add another job ->
pthreadpool_add_job()
-> pthreadpool_put_job()
This adds the job to the queue.
Oh, there is an idle thread so don't
create one, do:
pthread_cond_signal(&pool->condvar);
and return.
Now call fork *before* idle thread in (a) wakes from
the signaling of pool->condvar.
In the parent (child is irrelevent):
Go into: pthreadpool_prepare() ->
pthreadpool_prepare_pool()
Set the variable to tell idle threads to exit:
pool->prefork_cond = &prefork_cond;
then wake them up with:
pthread_cond_signal(&pool->condvar);
This does nothing as the idle thread
is already awoken.
b) Idle thread wakes up and does:
Reduce idle thread count (num_idle = 0)
pool->num_idle -= 1;
Check if we're in the middle of a fork.
if (pool->prefork_cond != NULL) {
Yes we are, tell pthreadpool_prepare()
we are exiting.
pthread_cond_signal(pool->prefork_cond);
And exit.
pthreadpool_server_exit(pool);
return NULL;
}
So we come back from the fork in the parent with num_jobs = 1,
a job on the queue but no idle threads - and the code that
creates a new thread on job submission was skipped because
an idle thread existed at point (a).
OK, assuming that the previous explaination is correct, the
fix is to create a new pthreadpool context mutex:
pool->fork_mutex
and in pthreadpool_server(), when an idle thread wakes up and
notices we're in the prepare fork state, it puts itself to
sleep by waiting on the new pool->fork_mutex.
And in pthreadpool_prepare_pool(), instead of waiting for
the idle threads to exit, hold the pool->fork_mutex and
signal each idle thread in turn, and wait for the pool->num_idle
to go to zero - which means they're all blocked waiting on
pool->fork_mutex.
When the parent continues, pthreadpool_parent()
unlocks the pool->fork_mutex and all the previously
'idle' threads wake up (and you mention the thundering
herd problem, which is as you say vanishingly small :-)
and pick up any remaining job.
Bug: https://bugzilla.samba.org/show_bug.cgi?id=13179
Signed-off-by: Volker Lendecke <vl@samba.org>
Reviewed-by: Jeremy Allison <jra@samba.org>
This is implemented using cmocka and the __wrap override for
pthread_create.
BUG: https://bugzilla.samba.org/show_bug.cgi?id=13170
Signed-off-by: Christof Schmitt <cs@samba.org
Reviewed-by: Andreas Schneider <asn@samba.org>
Autobuild-User(master): Christof Schmitt <cs@samba.org>
Autobuild-Date(master): Fri Dec 8 13:54:20 CET 2017 on sn-devel-144
