Commit f6874fdc authored by Kenton Varda's avatar Kenton Varda

More clarifications.

parent d414eb19
...@@ -24,10 +24,18 @@ _UPDATE: There has been some confusion about what I'm claiming. I am NOT sayin ...@@ -24,10 +24,18 @@ _UPDATE: There has been some confusion about what I'm claiming. I am NOT sayin
promises alone (i.e. being asynchronous) constitutes "time travel". Cap'n Proto implements a promises alone (i.e. being asynchronous) constitutes "time travel". Cap'n Proto implements a
technique called Promise Pipelining which allows a new request to be formed based on the content technique called Promise Pipelining which allows a new request to be formed based on the content
of a previous result (in part or in whole) before that previous result is returned. Notice in the of a previous result (in part or in whole) before that previous result is returned. Notice in the
diagram that the result of foo() is being passed to bar()._ diagram that the result of foo() is being passed to bar(). Please
[see the docs]({{ site.baseurl }}rpc.html) or
[check out the calculator example](https://github.com/kentonv/capnproto/blob/master/c++/samples)
for more._
### Promises in C++ ### Promises in C++
_UPDATE: More confusion. This section is **not** about pipelining ("time travel"). This section
is just talking about implementing a promise API in C++. Pipelining is another feature on top of
that. Please [see the RPC page]({{ site.baseurl }}rpc.html) if you want to know more about
pipelining._
If you do a lot of serious Javascript programming, you've probably heard of If you do a lot of serious Javascript programming, you've probably heard of
[Promises/A+](http://promisesaplus.com/) and similar proposals. Cap'n Proto RPC introduces a [Promises/A+](http://promisesaplus.com/) and similar proposals. Cap'n Proto RPC introduces a
similar construct in C++. In fact, the API is nearly identical, and its semantics are nearly similar construct in C++. In fact, the API is nearly identical, and its semantics are nearly
......
...@@ -87,6 +87,8 @@ foo = root.open("foo"); # 1 ...@@ -87,6 +87,8 @@ foo = root.open("foo"); # 1
bar = foo.open("bar"); # 2 bar = foo.open("bar"); # 2
size = bar.size(); # 3 size = bar.size(); # 3
data = bar.read(0, size); # 4 data = bar.read(0, size); # 4
# The above is four calls but takes only one network
# round trip with Cap'n Proto!
{% endhighlight %} {% endhighlight %}
In such a high-latency scenario, making your interface elegant is simply not worth 4x the latency. In such a high-latency scenario, making your interface elegant is simply not worth 4x the latency.
...@@ -137,6 +139,11 @@ need to change our interface at all. We keep our simple, elegant, singleton-fre ...@@ -137,6 +139,11 @@ need to change our interface at all. We keep our simple, elegant, singleton-fre
don't have to implement path strings, caching, authentication, or authorization, and yet everything don't have to implement path strings, caching, authentication, or authorization, and yet everything
performs as well as we can possibly hope for. performs as well as we can possibly hope for.
#### Example code
[The calculator example](https://github.com/kentonv/capnproto/blob/master/c++/samples/calculator-client.c++)
uses promise pipelining. Take a look at the client side in particular.
### Distributed Objects ### Distributed Objects
As you've noticed by now, Cap'n Proto RPC is a distributed object protocol. Interface references -- As you've noticed by now, Cap'n Proto RPC is a distributed object protocol. Interface references --
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