@milancurcic Thanks again for directing me to the book! I will have to read chapter 9 and 10 thoroughly before I am able to make any serious conclusion. BTW, is that possible for me to accept more than one replies as solutions? Currently I am only allowed to select one.
@nncarlson Yes, I read your post about coarray and definitely understand your concern, but coarray is a very attractive feature for me (and probably many other domain scientists) because it is standard conforming, and the syntax of it is just elegant. Personally, I am inclined to use it if the performance penalty isn’t unacceptable. I will come back for the testing part once I have my co_alltoall implemented. Thank you for your suggestions!