Fixes h2database/h2database#467 Deadlock between Sequence.flush() and Database.close()

h2/src/main/org/h2/engine/Database.java

@@ -1216,7 +1216,8 @@ public class Database implements DataHandler {
      * @param fromShutdownHook true if this method is called from the shutdown
      *            hook
      */
-    synchronized void close(boolean fromShutdownHook) {
+    void close(boolean fromShutdownHook) {
+        synchronized (this) {
             if (closing) {
                 return;
             }
@@ -1256,6 +1257,7 @@ public class Database implements DataHandler {
                 }
                 closing = true;
             }
+        }
         removeOrphanedLobs();
         try {
             if (systemSession != null) {

h2/src/main/org/h2/schema/Sequence.java

@@ -32,7 +32,7 @@ public class Sequence extends SchemaObjectBase {
     private long maxValue;
     private boolean cycle;
     private boolean belongsToTable;
-    private Object flushSync = new Object();
+    private final Object flushSync = new Object();
     private boolean writeWithMargin;
 
     /**
@@ -294,22 +294,19 @@ public class Sequence extends SchemaObjectBase {
             // locked it) because it must be committed immediately, otherwise
             // other threads can not access the sys table.
             Session sysSession = database.getSystemSession();
-            synchronized (sysSession) {
-                synchronized (flushSync) {
+            synchronized (database.isMultiThreaded() ?  sysSession : database) {
                 flushInternal(sysSession);
-                }
                 sysSession.commit(false);
             }
         } else {
-            synchronized (session) {
-                synchronized (flushSync) {
+            synchronized (database.isMultiThreaded() ? session : database) {
                 flushInternal(session);
             }
         }
     }
-    }
 
     private void flushInternal(Session session) {
+        synchronized (flushSync) {
             final boolean metaWasLocked = database.lockMeta(session);
             // just for this case, use the value with the margin
             try {
@@ -322,6 +319,7 @@ public class Sequence extends SchemaObjectBase {
                 database.unlockMeta(session);
             }
         }
+    }
 
     /**
      * Flush the current value to disk and close this object.

h2/src/test/org/h2/test/synth/TestKillRestart.java

@@ -26,11 +26,6 @@ public class TestKillRestart extends TestBase {
         if (config.networked) {
             return;
         }
-        if (config.fast) {
-            // using fast as a proxy for "running on Jenkins CI" where this test
-            // gets stuck waiting for the sub-process after killing it
-            return;
-        }
         if (getBaseDir().indexOf(':') > 0) {
             return;
         }

h2/src/test/org/h2/test/synth/TestKillRestartMulti.java

@@ -39,11 +39,6 @@ public class TestKillRestartMulti extends TestBase {
         if (config.networked) {
             return;
         }
-        if (config.fast) {
-            // using fast as a proxy for "running on Jenkins CI" where this test
-            // gets stuck waiting for the sub-process after killing it
-            return;
-        }
         if (getBaseDir().indexOf(':') > 0) {
             return;
         }