Fix: Handle both agent config files pointing to same port

The expected locations for the user and root agent sessiond
configuration files are ~/.lttng/agent.port and
/var/run/lttng/agent.port, respectively. These files indicate
which port an agent should connect to to reach its respective
sessiond.

If by some bad luck both files indicate the same port, then
both Java TCP clients would end up connecting to the same
sessiond, resulting in weird results, like "lttng list" listing
all events twice.

Make sure the target ports are different, and avoid duplicate
connections in case there are not.

Signed-off-by: Alexandre Montplaisir <alexmonthy@efficios.com>
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>

diff --git a/liblttng-ust-java-agent/java/lttng-ust-agent-common/org/lttng/ust/agent/client/LttngTcpSessiondClient.java b/liblttng-ust-java-agent/java/lttng-ust-agent-common/org/lttng/ust/agent/client/LttngTcpSessiondClient.java
index 84ad973f3cea5f0cdc56194eac4604fbb0dc2141..793a5f8e0b42cc12038117528376c96caa0134ff 100644 (file)
--- a/liblttng-ust-java-agent/java/lttng-ust-agent-common/org/lttng/ust/agent/client/LttngTcpSessiondClient.java
+++ b/liblttng-ust-java-agent/java/lttng-ust-agent-common/org/lttng/ust/agent/client/LttngTcpSessiondClient.java
@@ -158,23 +158,27 @@ public class LttngTcpSessiondClient implements Runnable {
        }
 
        private void connectToSessiond() throws IOException {
-               int port;
+               int rootPort = getPortFromFile(ROOT_PORT_FILE);
+               int userPort = getPortFromFile(getHomePath() + USER_PORT_FILE);
 
-               if (this.isRoot) {
-                       port = getPortFromFile(ROOT_PORT_FILE);
-                       if (port == 0) {
-                               /* No session daemon available. Stop and retry later. */
-                               throw new IOException();
-                       }
-               } else {
-                       port = getPortFromFile(getHomePath() + USER_PORT_FILE);
-                       if (port == 0) {
-                               /* No session daemon available. Stop and retry later. */
-                               throw new IOException();
-                       }
+               /*
+                * Check for the edge case of both files existing but pointing to the
+                * same port. In this case, let the root client handle it.
+                */
+               if ((rootPort != 0) && (rootPort == userPort) && (!isRoot)) {
+                       log("User and root config files both point to port " + rootPort +
+                                       ". Letting the root client handle it.");
+                       throw new IOException();
+               }
+
+               int portToUse = (isRoot ? rootPort : userPort);
+
+               if (portToUse == 0) {
+                       /* No session daemon available. Stop and retry later. */
+                       throw new IOException();
                }
 
-               this.sessiondSock = new Socket(SESSION_HOST, port);
+               this.sessiondSock = new Socket(SESSION_HOST, portToUse);
                this.inFromSessiond = new DataInputStream(sessiondSock.getInputStream());
                this.outToSessiond = new DataOutputStream(sessiondSock.getOutputStream());
        }