Steve, > I see your point, but the problem is that I cannot know when the receiver > is going to be executes and so when it will receive the data. > > Is there a way to wait on this channel until some task connects to and > make a get? This way I can keep the channel (and the task) alive until the > data has been consumed. I think there should be some mechanism to say > “wait for N tasks to connect”.
That's part of the deeper problem I hinted at. Let me think about this some more before I respond. > I am reporting my other question: > More in general, when you have many channels at scale, do you > think is better to use a register_as/connect_to mechanism or to pass alle > the necessary channels to each locality at the beginning when I do the > initial SPMD spawn? We usually use the register_as/connect_to mechanism as it separates concerns nicely. But YMMV, so please try it out for yourself what works best in your case. Sending a channel over the wire might overcome the lifetime issues we're discussing as this would keep the channel alive no matter what. Regards Hartmut --------------- http://boost-spirit.com http://stellar.cct.lsu.edu > > Thank you, > Steve > > > > > > On 12 Oct 2017, at 09:28, Hartmut Kaiser <[email protected]> wrote: > > Steve, > > > Going back to the channels discussion, how do you know if a channel has > been already registered or not? > > Look at the following code below (running with 2 localities): > - they create or connect to the same channel name > - if I introduce a delay in the receiver locality I get the following > error: > > Assertion failed: (buffer_map_.empty()), function ~receive_buffer, > file hpx_install/include/hpx/lcos/local/receive_buffer.hpp, line 101. > > I think I understand what is going on. This assert says that you're trying > to destroy a channel with data sitting in the pipeline. This is caused by > your code: > > { > hpx::lcos::channel<int> c(hpx::find_here()); > c.register_as(“name"); > c.set(3); > } > > Which makes the channel go out of scope before the other locality had a > chance to connect and to extract the value. > > There is also a deeper problem lurking behind the scenes, but that's > something I need to think about more before doing anything about it. > > Regards Hartmut > --------------- > http://boost-spirit.com > http://stellar.cct.lsu.edu > > > > Here is the sample code: > ————————— > > > void spmd_int(DataFlow::ShardId cid){ > if(cid%2==0){ > hpx::lcos::channel<int> c(hpx::find_here()); > c.register_as(“name"); > c.set(3); > } > else{ > usleep(1000000); // delay > hpx::lcos::channel<int> c; > c.connect_to("name"); > hpx::future<int> p = c.get(); > p.get(); > } > } > > > int hpx_main(boost::program_options::variables_map& vm){ > std::vector<hpx::naming::id_type> localities = > hpx::find_all_localities(); > > int loc_count = 0; > for(auto loc: localities){ > > spmd_int_action act; > hpx::async(act, loc, loc_count); > > loc_count++; > } > } > > ————————— > > > What is happening here? > If I add a > c.connect_to("name"); > > to the the same task that does the registration (after > c.register_as(“name");) it works, but I don’t like it (and in my actual > application I still get this error). > > More in general, when you have many of this channels at scale, do you > think is better to use a register_as/connect_to mechanism or to pass alle > the necessary channels to each locality at the beginning when I do the > initial SPMD spawn? > > Thanks, > Steve > > > On 11 Oct 2017, at 14:53, Steve Petruzza <[email protected]> wrote: > > Thanks Hartmut, it all makes sense now. > > > > On 11 Oct 2017, at 14:51, Hartmut Kaiser <[email protected]> wrote: > > > > I think I’ve found a workaround. > > If I use a typedef as following: > > typedef std::vector<char> vec_char; > > HPX_REGISTER_CHANNEL(vec_char); > > It works, but if I try to use directly: > HPX_REGISTER_CHANNEL(std::vector<char>) > > this gives me the error I reported before. > The issue might be in the expansion of the macro HPX_REGISTER_CHANNEL. > > Yes, that confirms my suspicion. I will have a looks what's going on. > > Doh! The problem is that the (literal) parameter you give to the macro has > to conform to the rules of a valid symbol name, i.e. no special characters > are allowed (no '<', '>', etc.). Sorry, this has to be documented properly > somewhere, and I forgot to mention it in the first place. > > The 'workaround' you propose is the only way to circumvent problems. There > is nothing we can do about it. > > Also, wrt your comment that everything is working if you use > hpx::lcos::local::channel instead - this is not surprising. The local > channel type is representing a channel which can be used inside a given > locality only (no remote operation, just inter-thread/inter-task > communication), hence its name. Those channels don't require the use of > the ugly macros, thus there is no problem. > > HTH > Regards Hartmut > --------------- > http://boost-spirit.com > http://stellar.cct.lsu.edu > > > > > Thanks! > Regards Hartmut > --------------- > http://boost-spirit.com > http://stellar.cct.lsu.edu > > > > > Steve > > > > > On 10 Oct 2017, at 18:38, Steve Petruzza <[email protected]> wrote: > > Sorry, regarding the version that I am using it is the commit of your > split_future for vector: > > Adding split_future for std::vector > > - this fixes #2940 > > commit 8ecf8197f9fc9d1cd45a7f9ee61a7be07ba26f46 > > Steve > > > > On 10 Oct 2017, at 18:33, Steve Petruzza <[email protected]> wrote: > > hpx::find_here() > > _______________________________________________ hpx-users mailing list [email protected] https://mail.cct.lsu.edu/mailman/listinfo/hpx-users
