[zeromq-dev] "thread safe" sockets and ZMQ_FD

Thomas Rodgers rodgert at twrodgers.com
Sat Feb 21 17:51:13 CET 2015


On Sat, Feb 21, 2015 at 10:45 AM, Thomas Rodgers <rodgert at twrodgers.com>

> Which all brings us to my next question -
> Can we just move on to -std=c++11 for future libzmq versions? The big 3
> compilers (well mostly, Microsoft still presents a few issues) support
> C++11 at this point.
> Many of the issues below would just 'go away' with the use of std::mutex,
> std::unique_lock, and std::comdition_variable.
> On Saturday, February 21, 2015, Bjorn Reese <breese at mail1.stofanet.dk>
> wrote:
>> On 02/21/2015 04:44 PM, Doron Somech wrote:
>> > (https://github.com/zeromq/libzmq/blob/master/src/mailbox_safe.hpp)
>> have
>> I had a quick look at this class...
>> The workaround in the destructor is not thread-safe. Another thread
>> may enter and wait between the sync->unlock() and the end of the
>> destructor scope. You need to add a state variable to prevent this
>> from happening.
>> Furthermore, if another thread is waiting on the condition variable,
>> then the mutex is unlocked while it is waiting. You need to
>> notify (broadcast) the condition variable to wake up the other thread
>> and get it out of the class. You will most likely need to to add a
>> reference count to keep track of how many pending threads are waiting
>> in order to know when it is safe to exit the destructor.
>> The use of sync->lock() and sync->unlock() is not exception safe. I
>> suggest that you use a scoped lock instead of the explicit calls. Read
>> this for inspiration:
>>    http://en.cppreference.com/w/cpp/thread/unique_lock
>> The code does not handle spurious wakeups from the condition variable.
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