Merge pull request #2431 from ControlSystemStudio/pva_errorhandling

PVA error handling

Author: kasemir

core/pv/src/main/java/org/phoebus/pv/pva/PVA_PV.java

@@ -164,6 +164,27 @@ public VType get(final long timeout, final TimeUnit unit)
     @Override
     public void write(final Object new_value) throws Exception
     {
+        // With Channel Access, there are different protocol options
+        // for "put" vs. "put-callback".
+        // With PVA, it is currently unclear how to distinguish between
+        // these two. The PVA server might honor certain values in the
+        // "request", but that is not documented as part of the protocol.
+        // On one hand, we should 'get()' the result of the write to
+        // receive exceptions for read-only PVs.
+        // On the other hand, such a 'get()' could last a long time
+        // in case some detail in the 'request' caused the PVA server
+        // to perform a put-callback type of operation,
+        // and a GUI calling write() expect an immediate return.
+
+        // Perform a disconnect check right now to alert caller
+        // of clearly disconnected channel
+        if (isDisconnected(read()))
+            throw new IllegalStateException("Channel '" + getName() + "' is not connected");
+
+        // The channel could still disconnect in the middle of the write,
+        // the channel may be read-only or experience other errors
+        // that we'll only see as log messages since we don't want to
+        // wait in 'get()' here...
         channel.write(name_helper.getWriteRequest(), new_value);
     }
 

core/pva/src/main/java/org/epics/pva/client/GetRequest.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2019 Oak Ridge National Laboratory.
+ * Copyright (c) 2019-2022 Oak Ridge National Laboratory.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
@@ -104,7 +104,7 @@ public void handleResponse(final ByteBuffer buffer) throws Exception
         final byte subcmd = buffer.get();
         PVAStatus status = PVAStatus.decode(buffer);
         if (! status.isSuccess())
-            throw new Exception(channel + " Get Response for " + request + ": " + status);
+            fail(new Exception(channel + " Get Response for " + request + ": " + status));
 
         if (subcmd == PVAHeader.CMD_SUB_INIT)
         {
@@ -147,6 +147,12 @@ public void handleResponse(final ByteBuffer buffer) throws Exception
         }
     }
 
+    /** Handle failure by both notifying whoever waits for this request to complete
+     *  and by throwing exception
+     *
+     *  @param ex Error description
+     *  @throws Exception
+     */
     private void fail(final Exception ex) throws Exception
     {
         completeExceptionally(ex);

core/pva/src/main/java/org/epics/pva/client/PVAChannel.java

@@ -86,8 +86,12 @@ PVAClient getClient()
     ClientTCPHandler getTCP() throws Exception
     {
         final ClientTCPHandler copy = tcp.get();
+
+        // Channel Access reacts to read/write access while disconnected
+        // via IllegalStateException("Channel not connected.")
+        // Use the same exception, but add channel name
         if (copy == null)
-            throw new Exception("Channel '" + name + "' is not connected");
+            throw new IllegalStateException("Channel '" + name + "' is not connected");
         return copy;
     }
 

core/pva/src/main/java/org/epics/pva/client/PutRequest.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2019-2020 Oak Ridge National Laboratory.
+ * Copyright (c) 2019-2022 Oak Ridge National Laboratory.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
@@ -151,9 +151,17 @@ public void handleResponse(final ByteBuffer buffer) throws Exception
             fail(new Exception("Incomplete Put Response"));
         final int request_id = buffer.getInt();
         final byte subcmd = buffer.get();
-        PVAStatus status = PVAStatus.decode(buffer);
+        final PVAStatus status = PVAStatus.decode(buffer);
         if (! status.isSuccess())
-            throw new Exception(channel + " Put Response for " + request + ": " + status);
+        {
+            // Server reported an error with text like "Put not permitted"
+            // for EPICS 7.0.6 QSRV.
+            // Channel access similarly provided an Exception with text
+            // "No write access rights granted."
+            // Not trying to parse the message; passing it up with added
+            // channel name and request info.
+            fail(new Exception(channel + " Write for '" + channel.getName() + "' " + request + " failed with " + status));
+        }
 
         if (subcmd == PVAHeader.CMD_SUB_INIT)
         {
@@ -186,9 +194,15 @@ else if (subcmd == PVAHeader.CMD_SUB_DESTROY)
             complete(null);
         }
         else
-            throw new Exception("Cannot decode Put " + subcmd + " Reply #" + request_id);
+            fail(new Exception("Cannot decode Put " + subcmd + " Reply #" + request_id));
     }
 
+    /** Handle failure by both notifying whoever waits for this request to complete
+     *  and by throwing exception
+     *
+     *  @param ex Error description
+     *  @throws Exception
+     */
     private void fail(final Exception ex) throws Exception
     {
         completeExceptionally(ex);

core/pva/src/test/java/org/epics/pva/client/ClientDemo.java

@@ -1,5 +1,5 @@
 /*******************************************************************************
- * Copyright (c) 2019-2020 Oak Ridge National Laboratory.
+ * Copyright (c) 2019-2022 Oak Ridge National Laboratory.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
@@ -94,12 +94,23 @@ public void testGet() throws Exception
         final PVAChannel ch2 = pva.getChannel("saw", listener);
         CompletableFuture.allOf(ch1.connect(), ch2.connect()).get(5, TimeUnit.SECONDS);
 
+        System.out.println("Connected.. Stop IOC in next 10 seconds to test disconnect");
+        TimeUnit.SECONDS.sleep(10);
+
         // Get data
-        Future<PVAStructure> data = ch1.read("");
-        System.out.println(ch1.getName() + " = " + data.get());
+        try
+        {
+            Future<PVAStructure> data = ch1.read("");
+            System.out.println(ch1.getName() + " = " + data.get());
 
-        data = ch2.read("");
-        System.out.println(ch2.getName() + " = " + data.get());
+            data = ch2.read("");
+            System.out.println(ch2.getName() + " = " + data.get());
+        }
+        catch (Exception ex)
+        {
+            System.out.println("Read failed");
+            ex.printStackTrace();
+        }
 
         // Close channels
         ch2.close();
@@ -263,18 +274,39 @@ public void testStatic() throws Exception
         pva.close();
     }
 
+    /** Write ('put') test
+     *
+     *  Includes a pause to allow manual stopping of the server.
+     *
+     *  May be used with read-only access security on IOC
+     *  to test failed write.
+     */
     @Test
     public void testPut() throws Exception
     {
         // Create a client
         final PVAClient pva = new PVAClient();
 
         // Connect to one or more channels
-        final PVAChannel channel = pva.getChannel("ramp");
+        final PVAChannel channel = pva.getChannel("saw");
         channel.connect().get(5, TimeUnit.SECONDS);
 
+
+        System.out.println("CONNECTED!");
+        System.out.println("Optionally stop the IOC within the next 10 seconds...");
+        TimeUnit.SECONDS.sleep(10);
+        System.out.println("Writing '2'...");
+
         // Write data
-        channel.write("value", 2.0).get(2, TimeUnit.SECONDS);
+        try
+        {
+            channel.write("value", 2.0).get(2, TimeUnit.SECONDS);
+        }
+        catch (Exception ex)
+        {
+            System.out.println("Write failed");
+            ex.printStackTrace();
+        }
 
         // Close channels
         channel.close();

core/pva/src/test/resources/demo.acf

@@ -0,0 +1,8 @@
+# Test read-only PVs:
+#
+# softIocPVA -m N='' -d demo.db -a demo.acf
+
+ASG(DEFAULT)
+{
+   RULE(1, READ)
+}