[CppAD] Multi-threading with TBB?

[Brad Bell]

One needs a separate copy of a tape for each thread.
This is because there is information stored along with the operation sequence that is the tape.

It is possible to make one tape recording, then make multiple copies of the tape using the 
assignment operator
http://coin-or.github.io/CppAD/doc/funconstruct.htm#Assignment%20Operator
Then uses a separate copy for each thread.

On 12/19/2018 12:11 PM, Perry de Valpine wrote:
> Thanks for the quick reply.
>
> I had already been through the documentation you pointed me to.
>
> Did my question about recording tapes vs. using tapes make sense?  The examples seem to show each 
> thread both recording and using its own tape.  What I understand from the documentation is that 
> CppAD's multi-thread tools are necessary because internally some globals are used, so CppAD needs 
> to be told to manage separate copies of those globals for each thread.  My question was whether 
> that is the case just for recording tapes or also for using tapes, which might have been recorded 
> and copied in serial execution?  If my question doesn't make sense, I'd probably benefit from any 
> explanation you can offer.
>
> Also can you help me understand the difference between the thread_num function that is passed to 
> thread_alloc::parallel_setup vs. thread_alloc::thread_num 
> (https://coin-or.github.io/CppAD/doc/ta_thread_num.htm)? Does the latter call the former?
>
> Thanks again.
>
> On Wed, Dec 19, 2018 at 10:08 AM Brad Bell <bradbell at seanet.com <mailto:bradbell at seanet.com>> wrote:
>
>     Here is the link to the key CppAD requirements for multi-threading
>     https://urldefense.proofpoint.com/v2/url?u=https-3A__coin-2Dor.github.io_CppAD_doc_ta-5Fparallel-5Fsetup.htm&d=DwIGaQ&c=Ngd-ta5yRYsqeUsEDgxhcqsYYY1Xs5ogLxWPA_2Wlc4&r=dGUSP0mcZ-4eFJdLgjemIUFvQwbOKo1wqmE_55NIGdc&m=Uc1__A27KLDN7APwoeTDVj5NwsKADcvMO9r-o1yZWS4&s=kFwgcVYei9YZYEdnnAJfV3EyhG0Ag7dl21aNJ4w-URc&e=
>
>     CppAD has to know a maximum number of threads, and which thread is currently running.
>     It seems from
>     https://urldefense.proofpoint.com/v2/url?u=https-3A__stackoverflow.com_questions_3786408_number-2Dof-2Dthreads-2Dused-2Dby-2Dintel-2Dtbb&d=DwIGaQ&c=Ngd-ta5yRYsqeUsEDgxhcqsYYY1Xs5ogLxWPA_2Wlc4&r=dGUSP0mcZ-4eFJdLgjemIUFvQwbOKo1wqmE_55NIGdc&m=Uc1__A27KLDN7APwoeTDVj5NwsKADcvMO9r-o1yZWS4&s=ACu19InrLSfMxKYSzdCAiytyoiclPYCkFxbTa2cJCdQ&e=
>     that this is not possible in TBB, but I am not sure.
>
>     On 12/19/2018 10:50 AM, Perry de Valpine wrote:
>     > Hello.  I'm not sure if you prefer queries here or on GitHub.  This is a general question so
>     I'm
>     > sending it to this list.
>     >
>     > I'm trying to see whether CppAD's multi-threading features can fit well with Threading Building
>     > Blocks (TBB).  Has anyone combined these successfully?  The simplest TBB example is here:
>     >
>     https://urldefense.proofpoint.com/v2/url?u=https-3A__software.intel.com_en-2Dus_node_506057&d=DwIGaQ&c=Ngd-ta5yRYsqeUsEDgxhcqsYYY1Xs5ogLxWPA_2Wlc4&r=dGUSP0mcZ-4eFJdLgjemIUFvQwbOKo1wqmE_55NIGdc&m=Uc1__A27KLDN7APwoeTDVj5NwsKADcvMO9r-o1yZWS4&s=U5kKsJw4CWu16GI3oMRqLsIQ2kOhjXSWiLsB0gobId8&e=
>     . Since TBB abstracts away thread creation but CppAD
>     > seems to require explicit thread management, I'm not sure if they're a natural fit for each
>     > other.  I can start to see how it might be done but wanted to ask for any suggestions first
>     since
>     > I am relatively new to multi-threading issues.
>     >
>     > What I would like to do is create a tape in serial mode and then in parallel use multiple
>     copies
>     > of that tape. The CppAD examples all show each thread both creating and using a tape.   Is
>     what I
>     > want to do possible?  I would also like to do this for multiple tapes (of different operations)
>     > that all get created once and then used repeatedly in different places.
>     >
>     > Based on the statements on parallel_ad
>     (https://urldefense.proofpoint.com/v2/url?u=https-3A__coin-2Dor.github.io_CppAD_doc_parallel-5Fad.htm&d=DwIGaQ&c=Ngd-ta5yRYsqeUsEDgxhcqsYYY1Xs5ogLxWPA_2Wlc4&r=dGUSP0mcZ-4eFJdLgjemIUFvQwbOKo1wqmE_55NIGdc&m=Uc1__A27KLDN7APwoeTDVj5NwsKADcvMO9r-o1yZWS4&s=cxQ9bvZUkZ9p3DZ0g4O9ecRfplKTnAexABwQnXS2tpQ&e=),
>
>     > which are not totally clear to me (maybe because I lack the background), does one need to do
>     the
>     > parallel_setup and parallel_AD steps if multiple threads will be used only for running tapes
>     > (ADFun objects) but not making new tapes?
>     >
>     > Thanks for the great software.
>     >
>     > Perry
>     >
>     >
>     >
>     > _______________________________________________
>     > CppAD mailing list
>     > CppAD at list.coin-or.org <mailto:CppAD at list.coin-or.org>
>     >
>     https://urldefense.proofpoint.com/v2/url?u=https-3A__list.coin-2Dor.org_mailman_listinfo_cppad&d=DwIGaQ&c=Ngd-ta5yRYsqeUsEDgxhcqsYYY1Xs5ogLxWPA_2Wlc4&r=dGUSP0mcZ-4eFJdLgjemIUFvQwbOKo1wqmE_55NIGdc&m=Uc1__A27KLDN7APwoeTDVj5NwsKADcvMO9r-o1yZWS4&s=t3fua1j4WWrTlEaRrF1uxB5fhl6ha4p8-fOBdGdKc8s&e=
>
>     _______________________________________________
>     CppAD mailing list
>     CppAD at list.coin-or.org <mailto:CppAD at list.coin-or.org>
>     https://urldefense.proofpoint.com/v2/url?u=https-3A__list.coin-2Dor.org_mailman_listinfo_cppad&d=DwIGaQ&c=Ngd-ta5yRYsqeUsEDgxhcqsYYY1Xs5ogLxWPA_2Wlc4&r=dGUSP0mcZ-4eFJdLgjemIUFvQwbOKo1wqmE_55NIGdc&m=Uc1__A27KLDN7APwoeTDVj5NwsKADcvMO9r-o1yZWS4&s=t3fua1j4WWrTlEaRrF1uxB5fhl6ha4p8-fOBdGdKc8s&e=
>