From d6989f1e54104d09b8af6d22cf46ea4f6fc5f4dc Mon Sep 17 00:00:00 2001
From: Trygve Laugstøl <trygvis@inamo.no>
Date: Wed, 10 Sep 2014 00:12:30 +0200
Subject: o Initial import of postgresql LISTEN/NOTIFY code.

---
 .../java/io/trygvis/jz14/db/NativeListener.java    | 157 +++++++++++++++++++++
 1 file changed, 157 insertions(+)
 create mode 100644 src/main/java/io/trygvis/jz14/db/NativeListener.java

(limited to 'src/main/java/io/trygvis/jz14/db/NativeListener.java')

diff --git a/src/main/java/io/trygvis/jz14/db/NativeListener.java b/src/main/java/io/trygvis/jz14/db/NativeListener.java
new file mode 100644
index 0000000..c44a7cc
--- /dev/null
+++ b/src/main/java/io/trygvis/jz14/db/NativeListener.java
@@ -0,0 +1,157 @@
+package io.trygvis.jz14.db;
+
+import io.trygvis.jz14.db.DbListener.PostgresConnection;
+import org.postgresql.PGConnection;
+import org.postgresql.PGNotification;
+import org.slf4j.Logger;
+
+import java.sql.PreparedStatement;
+import java.sql.SQLException;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.atomic.AtomicBoolean;
+import java.util.function.Supplier;
+
+import static io.trygvis.jz14.db.DbListener.DbListenerConfig;
+import static io.trygvis.jz14.db.DbListener.NewItemCallback;
+import static java.lang.System.currentTimeMillis;
+import static java.lang.Thread.sleep;
+import static org.slf4j.LoggerFactory.getLogger;
+
+class NativeListener implements Listener {
+    private final Logger log = getLogger(getClass());
+
+    private final AtomicBoolean shouldRun = new AtomicBoolean(true);
+    private final DbListenerConfig config;
+    private final Supplier<PostgresConnection<PGConnection>> connectionSupplier;
+    private final NewItemCallback callback;
+
+    private PostgresConnection<PGConnection> c;
+    private long lastLiveCheck;
+
+    public NativeListener(DbListenerConfig config, Supplier<PostgresConnection<PGConnection>> connectionSupplier, NewItemCallback callback) {
+        this.config = config;
+        this.connectionSupplier = connectionSupplier;
+        this.callback = callback;
+    }
+
+    public synchronized void close() {
+        shouldRun.set(false);
+        notifyAll();
+    }
+
+    @Override
+    public void run() {
+        while (shouldRun.get()) {
+            try {
+                doIt();
+            } catch (Throwable e) {
+                log.error("doIt failed", e);
+                try {
+                    sleep(config.listenerFailureSleepInterval);
+                } catch (InterruptedException ex2) {
+                    if (!shouldRun.get()) {
+                        log.error("Got interrupted.", ex2);
+                    }
+                }
+            }
+        }
+    }
+
+    private void doIt() throws Exception {
+
+        if (c == null) {
+            log.debug("Connecting to database");
+
+            try {
+                c = connectAndListen();
+            } catch (Throwable ex) {
+                onError("Unable to connect to database", ex);
+                return;
+            }
+        }
+
+        long now = currentTimeMillis();
+
+        if (now - lastLiveCheck > config.listenerConnectionLiveCheckInterval) {
+            log.debug("Doing live check");
+            try {
+                doLiveCheck();
+                lastLiveCheck = now;
+            } catch (Exception ex) {
+                onError("Live check failed", ex);
+                return;
+            }
+        }
+
+        PGNotification[] notifications;
+        try {
+            notifications = c.underlying.getNotifications();
+        } catch (SQLException e) {
+            onError("Error while checking for notifications on connection.", e);
+            return;
+        }
+
+        if (notifications != null) {
+            List<String> strings = new ArrayList<>();
+            for (PGNotification notification : notifications) {
+                String parameter = notification.getParameter();
+                if (parameter == null) {
+                    continue;
+                }
+
+                parameter = parameter.trim();
+
+                if (!parameter.isEmpty()) {
+                    strings.add(parameter);
+                }
+            }
+
+            log.debug("Got notification: parameters={}", strings);
+
+            try {
+                callback.newItem(true, strings);
+            } catch (Exception ex) {
+                onError("Notification handler failed", ex);
+                return;
+            }
+        }
+
+        sleep(config.listenerSleepInterval);
+    }
+
+    private void onError(String msg, Throwable ex) throws InterruptedException {
+        log.info(msg, ex);
+
+        // Do a last attempt at closing the connection, the connection pool might appreciate it.
+        if (c != null) {
+            try {
+                c.close();
+            } catch (Throwable e) {
+                log.info("Exception when closing connection after error", e);
+            }
+        }
+        c = null;
+        log.info("Sleeping for {} ms after failure", config.listenerFailureSleepInterval);
+        sleep(config.listenerFailureSleepInterval);
+        log.info("Resuming work after failure");
+    }
+
+    private PostgresConnection<PGConnection> connectAndListen() throws SQLException {
+        PostgresConnection<PGConnection> c = connectionSupplier.get();
+        c.sqlConnection.setAutoCommit(true);
+
+        lastLiveCheck = currentTimeMillis();
+
+        PreparedStatement s = c.sqlConnection.prepareStatement("LISTEN \"" + config.name + "\"");
+        s.execute();
+        s.close();
+        return c;
+    }
+
+    private void doLiveCheck() throws SQLException {
+        PreparedStatement s = c.sqlConnection.prepareStatement("SELECT 1");
+        s.executeQuery().close();
+        s.close();
+    }
+}
-- 
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