deal with rare race condition in balance cache

When we create a balance cache, we lock the account, it is possible for another thread to post a GLTransaction, still uncommitted, that increases the last transaction ID. To prevent this without enforcing expensive locks on every account involving a GLTransaction post, we use a safe window (default to 1000, can be overriden but we believe 1000 is a safe value for use cases like jCard) when deciding the MaxID we use for a bcache entry.
jpos · Jun 10, 2016 · 11d56e4 · 11d56e4
1 parent 50e4e55
commit 11d56e4
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Showing 2 changed files with 13 additions and 6 deletions.
diff --git a/modules/minigl/src/main/java/org/jpos/gl/GLSession.java b/modules/minigl/src/main/java/org/jpos/gl/GLSession.java
@@ -45,6 +45,7 @@ public class GLSession {
     public static final short[] LAYER_ZERO = new short[] { 0 };
     public static final BigDecimal ZERO = new BigDecimal ("0.00");
     public static final BigDecimal Z    = new BigDecimal ("0");
+    private long SAFE_WINDOW = 1000L;
 
     /**
      * Construct a GLSession for a given user.
@@ -1066,10 +1067,9 @@ else if (acct.isFinalAccount()) {
                     balance[0] = chkp.getBalance();
                     txnCrit.add (Restrictions.gt ("postDate", chkp.getDate()));
                 }
-
             } else {
                 BalanceCache bcache = getBalanceCache (journal, acct, layersCopy);
-                if (bcache != null) {
+                if (bcache != null && bcache.getRef() <= maxId) {
                     balance[0] = bcache.getBalance();
                     entryCrit.add (Restrictions.gt("id", bcache.getRef()));
                 }
@@ -1267,9 +1267,9 @@ else if (acct.isFinalAccount()) {
         (Journal journal, Account acct, short[] layers)
         throws HibernateException, GLException
     {
-        return createBalanceCache (journal, acct, layers, getMaxGLEntryId());
+        return createBalanceCache (journal, acct, layers, getSafeMaxGLEntryId());
     }
-    public BigDecimal createBalanceCache
+    private BigDecimal createBalanceCache
         (Journal journal, Account acct, short[] layers, long maxId)
         throws HibernateException, GLException
     {
@@ -1768,6 +1768,12 @@ private long getMaxGLEntryId () {
         GLEntry entry = (GLEntry) crit.uniqueResult();
         return entry != null ? entry.getId() : 0L;
     }
+    private long getSafeMaxGLEntryId() {
+        return Math.max (getMaxGLEntryId()-SAFE_WINDOW, 0L);
+    }
+    public void overrideSafeWindow (long l) {
+        this.SAFE_WINDOW = l;
+    }
     private void recurseChildren (Account acct, List<Long> list) {
         for (Account a : acct.getChildren()) {
             if (a instanceof FinalAccount)

diff --git a/modules/minigl/src/test/java/org/jpos/gl/BalanceTest.java b/modules/minigl/src/test/java/org/jpos/gl/BalanceTest.java
@@ -33,6 +33,7 @@ public class BalanceTest extends TestBase {
 
     public void setUp () throws Exception {
         super.setUp();
+        gls.overrideSafeWindow(0L);
         tj = gls.getJournal ("TestJournal");
         cashUS      = gls.getFinalAccount ("TestChart", "111");
         cashPesos   = gls.getAccount ("TestChart", "112");
@@ -58,8 +59,8 @@ public void testBalancesAfterCheckpoint() throws Exception {
     }
     public void testBalanceCache() throws Exception {
         final Transaction tx1 = gls.beginTransaction();
-        gls.createBalanceCache (tj, root, GLSession.LAYER_ZERO, 10);
-        gls.createBalanceCache (tj, root, new short[] { 858 }, 10);
+        gls.createBalanceCache (tj, root, GLSession.LAYER_ZERO);
+        gls.createBalanceCache (tj, root, new short[] { 858 });
         tx1.commit ();
     }
     public void testBalanceCache2() throws Exception {