[jbossts-issues] [JBoss JIRA] Reopened: (JBTM-688) TransactionReaper synchronization is a performance bottleneck

TransactionReaper synchronization is a performance bottleneck ------------------------------------------------------------- Key: JBTM-688 URL: https://jira.jboss.org/jira/browse/JBTM-688 Project: JBoss Transaction Manager Issue Type: Patch Security Level: Public(Everyone can see) Components: JTS Affects Versions: 4.6.1.CP04 Environment: Linux 32-bit, Sun JDK 6 Reporter: Oleg Nitz Assignee: Andrew Dinn During stress testing I found that threads often massively block on synchronization on TransactionReaper.class, due to synchronized static methods create() and transactionReaper() in the TransactionReaper class. I propose to use "double-checked locking idiom" (see http://en.wikipedia.org/wiki/Double-checked_locking ) to avoid unnecesary synchronizations. My patch follows. --- TransactionReaper.java.orig 2010-01-04 16:27:21.000000000 +0200 +++ TransactionReaper.java 2010-01-11 17:19:55.000000000 +0200 @@ -1059,7 +1059,7 @@ * Could get priority from environment. */ - public static synchronized TransactionReaper create(long checkPeriod) + public static TransactionReaper create(long checkPeriod) { if (tsLogger.arjLogger.debugAllowed()) { @@ -1070,6 +1070,10 @@ if (TransactionReaper._theReaper == null) { + synchronized (TransactionReaper.class) { + if (TransactionReaper._theReaper == null) + { + // default to dynamic mode TransactionReaper._dynamic = true; @@ -1215,6 +1219,8 @@ _reaperWorkerThread.start(); } + } + } return TransactionReaper._theReaper; } @@ -1233,7 +1239,7 @@ * If parameter is true then do a create. */ - public static synchronized TransactionReaper transactionReaper( + public static TransactionReaper transactionReaper( boolean createReaper) { if (createReaper) @@ -1315,7 +1321,7 @@ */ private int _zombieMax = 0; - private static TransactionReaper _theReaper = null; + private static volatile TransactionReaper _theReaper = null; private static ReaperThread _reaperThread = null;