apache/cloudstack
1
0
Fork 0
mirror of https://github.com/apache/cloudstack.git synced 2025-11-02 20:02:29 +01:00
Code Issues Packages Projects Releases Wiki Activity

Use double check pattern to avoid holding two locks in GlobalLock.java while trying to perserve intern semantic of global lock

Browse Source
This commit is contained in:
kelven 2011-01-03 23:05:51 -08:00 committed by Kelven Yang
parent 4e10a97c87
commit 06b48945b1
2 changed files with 42 additions and 31 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
utils/src/com/cloud/utils/db/DbUtil.java
View File

@ -249,6 +249,7 @@ public class DbUtil {
Connection conn = getConnectionForGlobalLocks(name, false);
if(conn == null) {
s_logger.error("Unable to acquire DB connection for global lock system");
assert(false);
return false;
}

72
utils/src/com/cloud/utils/db/GlobalLock.java
View File

@ -67,18 +67,20 @@ public class GlobalLock {
public int releaseRef() {
int refCount;
synchronized(s_lockMap) { // // lock in sequence to prevent deadlock
synchronized(this) {
referenceCount--;
refCount = referenceCount;
if(referenceCount < 0)
s_logger.warn("Unmatched Global lock " + name + " reference usage detected, check your code!");
if(referenceCount == 0)
releaseInternLock(name);
}
}
boolean needToRemove = false;
synchronized(this) {
referenceCount--;
refCount = referenceCount;
if(referenceCount < 0)
s_logger.warn("Unmatched Global lock " + name + " reference usage detected, check your code!");
if(referenceCount == 0)
needToRemove = true;
}
if(needToRemove)
releaseInternLock(name);
return refCount;
}
@ -99,8 +101,12 @@ public class GlobalLock {
}
private static void releaseInternLock(String name) {
synchronized(s_lockMap) {
s_lockMap.remove(name);
synchronized(s_lockMap) {
GlobalLock lock = s_lockMap.get(name);
assert(lock != null);
if(lock.referenceCount == 0)
s_lockMap.remove(name);
}
}
@ -135,25 +141,29 @@ public class GlobalLock {
return false;
continue;
} else {
// we will discount the time that has been spent in previous waiting
} else {
// take ownership temporarily to prevent others enter into stage of acquiring DB lock
ownerThread = Thread.currentThread();
if(DbUtil.getGlobalLock(name, remainingMilliSeconds / 1000)) {
lockCount++;
holdingStartTick = System.currentTimeMillis();
// keep the lock in the intern map when we got the lock from database
addRef();
if(s_logger.isTraceEnabled())
s_logger.trace("lock " + name + " is acquired, lock count :" + lockCount);
return true;
} else {
ownerThread = null;
}
return false;
addRef();
}
}
}
if(DbUtil.getGlobalLock(name, remainingMilliSeconds / 1000)) {
synchronized(this) {
lockCount++;
holdingStartTick = System.currentTimeMillis();
if(s_logger.isTraceEnabled())
s_logger.trace("lock " + name + " is acquired, lock count :" + lockCount);
return true;
}
} else {
synchronized(this) {
ownerThread = null;
releaseRef();
return false;
}
}
}
} finally {
if(interrupted) {