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<h1>Module <a href="type_Versioned_rpc.html">Versioned_rpc</a></h1>
<pre><span class="keyword">module</span> Versioned_rpc: <code class="code">sig</code> <a href="Versioned_rpc.html">..</a> <code class="code">end</code></pre><div class="info module top">
Infrastructure code for managing RPCs which evolve over time to use
different types at different versions<br>
</div>
<hr width="100%">
<br>
This module contains infrastructure code for managing RPCs which evolve
over time to use different types at different versions. Three scenarios
are supported
<ul>
<li>The <i>caller</i> is responsible for managing versions and
dispatches to callees that are written in a version-oblivious
way.
<p>
The proto-typical example of this scenario is a commander that
needs to call out to many assistants for that same system.
In this scenario, the assistants each implement a single
version of the rpc and the commander has to take this into
account.
</li>
<li>The <i>callee</i> is responsible for managing versions and
callers need not bother themselves with any versions.
<p>
The proto-typical example of this scenario is an assistant
from one system calling out the commander of another system
In this scenario, the assistants each know a single version
of the rpc to call and the commander has to implement them
all.
</li>
<li>Both <i>caller</i> and <i>callee</i> cooperate to decide which version to use, each
one being able to use some subset of all possible versions.
<p>
The proto-typical example of this scenario is when two systems developed
independently with their rpc types defined in some shared library which has yet
another independent rollout schedule. In this case one may roll out a new rpc
version (V) in the shared library (L) and then the caller and callee systems can
each upgrade to the new version of L supporting version V at their own pace,
with version V only being exercised once both caller and callee have upgraded.
</li>
</ul>
<p>
In each scenario, it is desirable that the party responsible for
managing versions be coded largely in terms of a single "master"
version of the types involved, with all necessary type conversions
relegated to a single module. <code class="code">Versioned_rpc</code> is intended for
implementing such a module.
<p>
Type coercions into and out of the model go in the directions indicated
by the following diagram:
<pre class="verbatim">
Caller converts Callee converts
=============== ===============
caller callee
| callee | callee
| | caller | | callee
| | | | | |
,-->-- Q1 --> R1 -->-. Q1 -->-. | ,-->-- R1
/ \ \ | /
Q --->-- Q2 --> R2 -->-- R Q2 -->-- Q --> R --->-- R2
\ / / \
`-->-- Q3 --> R3 -->-' Q3 -->-' `-->-- R3
</pre><br>
<pre><span class="keyword">module</span> <a href="Versioned_rpc.Menu.html">Menu</a>: <code class="code">sig</code> <a href="Versioned_rpc.Menu.html">..</a> <code class="code">end</code></pre>
<pre><span class="keyword">module</span> <a href="Versioned_rpc.Connection_with_menu.html">Connection_with_menu</a>: <code class="code">sig</code> <a href="Versioned_rpc.Connection_with_menu.html">..</a> <code class="code">end</code></pre>
<pre><span class="keyword">module</span> <a href="Versioned_rpc.Caller_converts.html">Caller_converts</a>: <code class="code">sig</code> <a href="Versioned_rpc.Caller_converts.html">..</a> <code class="code">end</code></pre>
<pre><span class="keyword">module</span> <a href="Versioned_rpc.Callee_converts.html">Callee_converts</a>: <code class="code">sig</code> <a href="Versioned_rpc.Callee_converts.html">..</a> <code class="code">end</code></pre>
<pre><span class="keyword">module</span> <a href="Versioned_rpc.Both_convert.html">Both_convert</a>: <code class="code">sig</code> <a href="Versioned_rpc.Both_convert.html">..</a> <code class="code">end</code></pre></body></html>
