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new 5290970 Site checkin for project PLC4X: Jenkins Tools
5290970 is described below
commit 52909709cb76c8b4f8ca97ddc2b076b2c832cb0d
Author: jenkins <[email protected]>
AuthorDate: Fri Feb 5 02:03:36 2021 +0000
Site checkin for project PLC4X: Jenkins Tools
---
...{connection-pool.html => connection-cache.html} | 116 ++++-----------------
users/tools/connection-pool.html | 85 ---------------
2 files changed, 20 insertions(+), 181 deletions(-)
diff --git a/users/tools/connection-pool.html
b/users/tools/connection-cache.html
similarity index 84%
copy from users/tools/connection-pool.html
copy to users/tools/connection-cache.html
index 95d2f76..31c8333 100644
--- a/users/tools/connection-pool.html
+++ b/users/tools/connection-cache.html
@@ -223,7 +223,7 @@
<a href="../../users/tools/capture-replay.html"
class="nav-link">Capture Replay</a>
</li>
<li class="nav-item">
- <strong class="nav-link">Connection Pool</strong>
+ <a href="../../users/tools/connection-pool.html"
class="nav-link">Connection Pool</a>
</li>
<li class="nav-item">
<a href="../../users/tools/opm.html"
class="nav-link">Object PLC Mapping (OPM)</a>
@@ -282,104 +282,16 @@
</div>
</nav>
<main role="main"
class="ml-sm-auto px-4 col-sm-pull col-md-9 col-lg-10 h-100">
- <div class="sect1">
-<h2 id="connection_pool">Connection Pool</h2>
-<div class="sectionbody">
-<div class="paragraph">
-<p>There are situations where you don’t want to carry around connections
in your code.</p>
-</div>
-<div class="paragraph">
-<p>For example if you have a microservice application, you might have multiple
services accessing PLC data.</p>
-</div>
-<div class="paragraph">
-<p>Keeping an open connection for each of these is rather problematic as in
contrast to modern computers, PLCs usually are only able to manage a small
number of concurrent connections.</p>
-</div>
-<div class="paragraph">
-<p>I think a Siemens S7-1200 is limited to 7 concurrent connections and a
Siemens LOGO can’t do more than 3.</p>
-</div>
-<div class="paragraph">
-<p>One alternative would be to open and close the connections all the time.
-This however puts an unnecessary stress on the PLCs as for protocols like the
S7 or the ADS protocol a handshake of multiple requests and responses has to be
executed before being able to communicate.</p>
-</div>
-<div class="paragraph">
-<p>As usually these services only require ad-hoc access to a PLC, it would be
ideal to share connections between services.</p>
-</div>
-<div class="paragraph">
-<p>Another problem occurs when you open a connection and keep it open for a
prolonged time period.
-Here it can happen quite often that a connection is terminated because the PLC
has been turned off.</p>
-</div>
-<div class="paragraph">
-<p>Per default the PLC connection has no means of automatically
re-connecting.</p>
-</div>
-<div class="paragraph">
-<p>The <code>PooledPlcDriverManager</code> can help you with both of these
scenarios.</p>
-</div>
-<div class="sect2">
-<h3 id="the_pooledplcdrivermanager">The PooledPlcDriverManager</h3>
-<div class="paragraph">
-<p>The <code>PooledPlcDriverManager</code> is a wrapper around the normal
<code>PlcDriverManager</code>.</p>
-</div>
-<div class="paragraph">
-<p>The main difference is that as soon as a connection is requested, it will
look if one already exists and return that.</p>
-</div>
-<div class="paragraph">
-<p>If no connection exists it will create a new one and keep it in the
pool.</p>
-</div>
-<div class="paragraph">
-<p>There are no API differences from using the normal
<code>PlcDriverManager</code> so you call <code>createConnection</code> and
<code>close</code> just like with the normal PLC4X API.</p>
-</div>
-<div class="paragraph">
-<p>The structure of the code is now more or less like if you would create a
new connection for every request and close it afterwards.</p>
-</div>
-<div class="paragraph">
-<p>Another benefit of the <code>PooledPlcDriverManager</code> is that it will
check a connection for any problems before returning it to the client.</p>
-</div>
-<div class="paragraph">
-<p>So if a connection was terminated, it will detect this and create a new
connection.</p>
-</div>
-</div>
-<div class="sect2">
-<h3 id="example">Example</h3>
-<div class="paragraph">
-<p>Here comes a little example program utilizing the
<code>PooledPlcDriverManager</code>:</p>
-</div>
-<div class="listingblock">
-<div class="content">
-<pre class="prettyprint highlight"><code data-lang="java"> PlcDriverManager
driverManager = new PooledPlcDriverManager();
-
- // This just simulates a scenario where a lot of connections would be
created and immediately destroyed again.
- for(int i = 0; i < 100; i++) {
- try(PlcConnection connection = driverManager.getConnection("...")) {
-
- ... do something ... (please refer to the PLC4J getting started
for details)
-
- }
- }</code></pre>
-</div>
-</div>
-<div class="admonitionblock note">
-<table>
-<tr>
-<td class="icon">
-<i class="fa icon-note" title="Note"></i>
-</td>
-<td class="content">
-When sharing connections between multiple services, be sure to share the
instance of the <code>PooledPldDriverManager</code> as otherwise you will
result in having multiple pools.
-</td>
-</tr>
-</table>
-</div>
-</div>
-<div class="sect2">
-<h3 id="the_cacheddrivermanager">The CachedDriverManager</h3>
+ <div class="sect2">
+<h3 id="the_connection_cache_concept">The Connection Cache concept</h3>
<div class="paragraph">
<p>There’s an another version of pool manager with similar target but
different implementation.</p>
</div>
<div class="paragraph">
-<p>The idea behind this second pool driver is that a connection could be lost
for a lot of external reason without the possibility to handle those from the
plc4x point of view (e.g. the cable is unplugged in a reading session). In the
Cached Pool Manager every connection could be used for only a limited period of
time, at the end the connection is no more valid and must be returned to the
poll.</p>
+<p>The idea behind this second pool driver is that a connection could be lost
for a lot of external reason, without the possibility to handle those from the
plc4x point of view (e.g. the cable is unplugged in a reading session). In the
Cached Pool Manager every connection could be used for only a limited period of
time, at the end the connection is no more valid and must be returned to the
poll.</p>
</div>
<div class="paragraph">
-<p>Even in the Cached Pool Manager, like before, getting a connection from the
pool is effortless so the typical live cycle of a connection is:</p>
+<p>Even in the Cached Pool Manager, getting a connection from the pool is
effortless so the typical live cycle of a connection is:</p>
</div>
<div class="listingblock">
<div class="content">
@@ -390,7 +302,7 @@ When sharing connections between multiple services, be sure
to share the instanc
<p>In the Cached Pool Manager a watchdog will invalidate any open connection
at the end of it’s live time even if no answer came back from the PLC; in
this case the library could continue to talk to the PLC with some other
connections fetched from the pool.</p>
</div>
<div class="paragraph">
-<p>Let explain this concept in more detail using the Cached Pool with a
modified version of the previous example:</p>
+<p>Let explain this concept in more detail using the Cached Pool with an
example:</p>
</div>
<div class="listingblock">
<div class="content">
@@ -429,6 +341,20 @@ When sharing connections between multiple services, be
sure to share the instanc
}</code></pre>
</div>
</div>
+<div class="admonitionblock note">
+<table>
+<tr>
+<td class="icon">
+<i class="fa icon-note" title="Note"></i>
+</td>
+<td class="content">
+<div class="paragraph">
+<p>To use the Connection Cache you have to add to Maven the latest version of
<code>plc4j-connection-cache</code> and import <code>CachedDriverManager</code>
into your code</p>
+</div>
+</td>
+</tr>
+</table>
+</div>
<div class="paragraph">
<p>In this snippet of code there are some considerations that are worth to be
underlined.</p>
</div>
@@ -455,8 +381,6 @@ When sharing connections between multiple services, be sure
to share the instanc
<p>All the others exceptions (i.e. <code>ExecutionException</code> and
<code>CancellationException</code>) are thread java related exceptions; in this
example these are caught to show how plc4x could be used to handle all the
external problems that could happen in talking to a PLC and could recover from
them.</p>
</div>
</div>
-</div>
-</div>
</main>
<footer class="pt-4 my-md-5 pt-md-5 w-100 border-top">
<div class="row justify-content-md-center" style="font-size: 13px">
diff --git a/users/tools/connection-pool.html b/users/tools/connection-pool.html
index 95d2f76..47efd57 100644
--- a/users/tools/connection-pool.html
+++ b/users/tools/connection-pool.html
@@ -370,91 +370,6 @@ When sharing connections between multiple services, be
sure to share the instanc
</table>
</div>
</div>
-<div class="sect2">
-<h3 id="the_cacheddrivermanager">The CachedDriverManager</h3>
-<div class="paragraph">
-<p>There’s an another version of pool manager with similar target but
different implementation.</p>
-</div>
-<div class="paragraph">
-<p>The idea behind this second pool driver is that a connection could be lost
for a lot of external reason without the possibility to handle those from the
plc4x point of view (e.g. the cable is unplugged in a reading session). In the
Cached Pool Manager every connection could be used for only a limited period of
time, at the end the connection is no more valid and must be returned to the
poll.</p>
-</div>
-<div class="paragraph">
-<p>Even in the Cached Pool Manager, like before, getting a connection from the
pool is effortless so the typical live cycle of a connection is:</p>
-</div>
-<div class="listingblock">
-<div class="content">
-<pre class="prettyprint highlight"><code>Get a connection -> use the
connection -> return the connection to the pool</code></pre>
-</div>
-</div>
-<div class="paragraph">
-<p>In the Cached Pool Manager a watchdog will invalidate any open connection
at the end of it’s live time even if no answer came back from the PLC; in
this case the library could continue to talk to the PLC with some other
connections fetched from the pool.</p>
-</div>
-<div class="paragraph">
-<p>Let explain this concept in more detail using the Cached Pool with a
modified version of the previous example:</p>
-</div>
-<div class="listingblock">
-<div class="content">
-<pre class="prettyprint highlight"><code data-lang="java"> public static
void main(String[] args) throws Exception {
- String connectionString = "s7://192.168.1.192";
- PlcDriverManager manager = new PlcDriverManager();
- PlcDriverManager cached = new
CachedDriverManager(connectionString,() ->
manager.getConnection(connectionString));
- for (int i = 0; i < 10000; i++) {
- try {
- TimeUnit.MILLISECONDS.sleep(500);
- try (PlcConnection conn =
cached.getConnection(connectionString)) {
- if (conn.isConnected()){
- PlcReadRequest.Builder builder =
conn.readRequestBuilder();
- builder.addItem("PollingValue", "%DB1:4.0:BOOL");
- PlcReadRequest readRequest = builder.build();
- PlcReadResponse syncResponse =
readRequest.execute().get(2000, TimeUnit.MILLISECONDS);
- printResponse(syncResponse);
- } else {
- logger.info("PLC is not connected, let's try again
to connect");
- conn.connect();
- }
- }
- } catch (PlcConnectionException e){
- logger.error("Connection exception in trying to connect",
e);
- } catch (CancellationException e){
- logger.error("Polling Thread canceled", e);
- } catch (IllegalStateException e){
- logger.error("Error in Netty state machine", e);
- } catch (ExecutionException e){
- logger.error("Interrupted Exception fired", e);
- } catch (TimeoutException e) {
- logger.error("Timeout exception fired", e);
- }
- }
- System.exit(0);
- }</code></pre>
-</div>
-</div>
-<div class="paragraph">
-<p>In this snippet of code there are some considerations that are worth to be
underlined.</p>
-</div>
-<div class="ulist">
-<ul>
-<li>
-<p>The <code>try-with-resources</code> statement (i.e. <code>try
(PlcConnection conn = cached.getConnection(connectionString))</code>) ensure
that an open connection will be automatically closed and returned to the pool
after the use. As said before if the connection get stuck for any reason, after
a fixed amount of time will be killed by a software watchdog (i.e. the amount
of time is now fixed to 5000 ms, will be configurable in the future);</p>
-</li>
-<li>
-<p>Check if the PLC is connected before reading some data is always advisable
(i.e. <code>conn.isConnected()</code>) but this doesn’t mean that the PLC
will be ready to answer to the connection, it means that the initial handshake
went good and plc4x has the needed information to talk with the PLC;</p>
-</li>
-<li>
-<p>the use of <code>get()</code> must be done with a timeout (i.e.
<code>readRequest.execute().get(2000, TimeUnit.MILLISECONDS)</code>). After the
timeout amount of time a <code>TimeoutException</code> will be fired. In the
code this is trapped and signaled with a simple line of log. This case could
happen because the PLC for some reason could decide to not answer or the
physical connection could have some problem;</p>
-</li>
-<li>
-<p>the <code>PlcConnectionException</code> is a connection error that could
happen in the handshaking phase between the PLC4x library and the PLC.
It’s a generic error;</p>
-</li>
-<li>
-<p>the <code>IllegalStateException</code> is a Netty library exception which
could happen in some really troubled connection, mostly if a physical
disconnection happen.</p>
-</li>
-</ul>
-</div>
-<div class="paragraph">
-<p>All the others exceptions (i.e. <code>ExecutionException</code> and
<code>CancellationException</code>) are thread java related exceptions; in this
example these are caught to show how plc4x could be used to handle all the
external problems that could happen in talking to a PLC and could recover from
them.</p>
-</div>
-</div>
</div>
</div>
</main>
