Ruby » Ruby master

Feature #17298

Updated by Dan0042 (Daniel DeLorme) over 3 years ago

This ticket proposes `send_basket`/`receive_basket`, `send_basket`/`send_receive`, `yield_basket`/`take_basket` APIs to make effective and flexible bridge ractors. 

 ## Background 

 When we want to send an object as a message, we usually need to copy it. Copying is achieved according to marshal protocol, and the receiver loads it immediately. 

 If we want to make a bridge ractor that receives a message and sends it to another ractor, immediate loading is not effective. 

 ```ruby 
 bridge = Ractor.new do 
   Ractor.yield Ractor.receive 
 end 

 consumer = Ractor.new bridge do |from| 
   obj = from.take 
   do_task(obj) 
 end 

 msg = [1, 2, 3] 
 bridge.send msg 
 ``` 

 In this case, the array (`[1, 2, 3]`) is 

 * (1) dumped at the first `bridge.send msg` 
 * (2) loaded at `Ractor.receive` 
 * (3) dumped again at `Ractor.yield` 
 * (4) loaded at `from.take` 

 Essentially, we only need one dump/load pair, but now it needs two pairs. 

 Mixing "moving" status is more complex. Now there is no way to pass the "moving" status to bridge ractors, so we cannot make a moving bridge. 

 ## Proposal 

 To make more effective and flexible bridge ractors, we propose new basket APIs 

 * `Ractor.receive_basket` 
 * `Ractor#send_basket` 
 * `Ractor#take_basket` `Ractor.take_basket` 
 * `Ractor.yield_basket` 

 They receive a message, retains the dumped state, and sends it without dumping again. We can rewrite the above example with these APIs. 

 ```ruby 
 bridge = Ractor.new do 
   Ractor.yield_basket Ractor.receive_basket 
 end 

 consumer = Ractor.new bridge do |from| 
   obj = from.take 
   do_task(obj) 
 end 

 msg = [1, 2, 3] 
 bridge.send msg 
 ``` 

 In this case, 

 * (1) dumped at the first `bridge.send msg` 
 * (2) loaded at `from.take` 

 we only need one dump/load pair. 

 ## Implementation 

 https://github.com/ruby/ruby/pull/3725 

 ## Evaluation 

 The following program makes four types of bridges and passes an array as a message through them. 

 ```ruby 
 USE_BASKET = false 

 receive2yield = Ractor.new do 
   loop do 
     if USE_BASKET 
       Ractor.yield_basket Ractor.receive_basket 
     else 
       Ractor.yield Ractor.receive 
     end 
   end 
 end 

 receive2send = Ractor.new receive2yield do |r| 
   loop do 
     if USE_BASKET 
       r.send_basket Ractor.receive_basket 
     else 
       r.send Ractor.receive 
     end 
   end 
 end 

 take2yield = Ractor.new receive2yield do |from| 
   loop do 
     if USE_BASKET 
       Ractor.yield_basket from.take_basket 
     else 
       Ractor.yield from.take 
     end 
   end 
 end 

 take2send = Ractor.new take2yield, Ractor.current do |from, to| 
   loop do 
     if USE_BASKET 
       to.send_basket from.take_basket 
     else 
       to.send from.take 
     end 
   end 
 end 

 AN = 1_000 
 LN = 10_000 

 ary = Array.new(AN) # 1000 
 LN.times{ 
   receive2send << ary 
   Ractor.receive 
 } 

 # This program passes the message as: 
 #     main -> 
 #     receive2send -> 
 #     receive2yield -> 
 #     take2yield -> 
 #     take2send -> 
 #     main 
 ``` 

 The result is: 

 ``` 
 w/ basket API     0m2.056s 
 w/o basket API    0m5.974s 
 ``` 

 on my machine (=~ x3 faster). 

 (BTW, if we have a TVar, we can change the value `USE_BASKET` dynamically) 

 ## Discussion 

 ### Naming 

 Of course, naming is an issue. Now, I named it "_basket" because the source code uses this terminology. There are other candidates: 

 * container metaphor 
   * package 
   * parcel 
   * box 
   * envelope 
   * packet (maybe bad idea because of confusion of networking) 
   * bundle (maybe bad idea because of confusion of bin/bundle) 
 * "don't touch the content" metaphor 
   * raw 
   * sealed 
   * unopened 

 I like "basket" because I like picnic. 

 ### Feature 

 Now, basket is represented by "Ractor::Basket" and there are no methods. We can add the following feature: 

 * `Ractor::Basket#sender` returns the sending ractor. 
 * `Ractor::Basket#sender = a_ractor` changes the sending ractor. 
 * `Ractor::Basket#value` returns the content. 

 There was another proposal `Ractor.recvfrom`, but we only need these APIs. 

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