Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.programming.threads > #4042

Re: Detecting mutexes owned by dead processes

Show all headers | View raw

I have my own lock solution which solves this problem but with some extra
work and ONLY for write locking.  This is so since my structure stores
only the last writer pid & thread in the structure.  Unfortunately, since read
locks are granted to multiple threads and since I do not store all the
threads which have so far acquired the read lock, the mechanism protects
only against write locks.  If one was to also add code to maintain the
entire list of reader threads, it would also work for reader crashes too
but that would make the lock object quite complicated.

I have a mutex and a bunch of counters & thread ids which are in
my own private lock structure.

When a read or write lock is requested, the code checks whether there
is currently a write lock already granted.  If so, AND the pid/thread
which currently has the write lock is NOT the same as the requesting 
pid/thread, there and then a quick check is made using the pid/thread id
of the current writer to see if it is alive.  If so, no problem, the 
write lock is not granted.  But if the pid/thread has already died, then
the lock is granted to the new requester.

Basically, what is being done is detecting whether a pid/thread is alive
only at the instance when another pid/thread requests the write lock.
This limits the liveness checking to be done only when the locks are
required and is not important any other times.

As I said at the beginning, since write lock is granted only to one thread
at a time, it is easy to do.  If it is required that "dead" threads be also
detected when readers are involved, a list of readers have to be maintained.

So make sure you crash only when u have the write lock & not the read lock :-)

Back to comp.programming.threads | Previous | Next — Next in thread | Find similar | Unroll thread

Thread

Re: Detecting mutexes owned by dead processes gee.akyol@gmail.com - 2018-02-02 13:16 -0800
  Re: Detecting mutexes owned by dead processes Kaz Kylheku <217-679-0842@kylheku.com> - 2018-02-02 23:47 +0000
  Re: Detecting mutexes owned by dead processes Steve Watt <steve.removethis@Watt.COM> - 2018-02-06 00:23 +0000

csiph-web