Here is a reference to double-checked locking. Many people have tried to get around synchronization during lazy initialization - AFAIK, none have succeeded. With the new memory model in Java5, you can get away with just volatile, which is like half a synchronization (a read barrier + a write barrier).
http://www.google.com/search?q=double+checked+locking -Yonik http://incubator.apache.org/solr Solr, the open-source Lucene search server On 5/9/06, yueyu lin <[EMAIL PROTECTED]> wrote:
In java, call a synchronized function in a synchronized block, if they have the same mutex object, nothing will happen. If they have different mutex objects, something may be screwed up. On 5/10/06, Yonik Seeley <[EMAIL PROTECTED]> wrote: > > Yueyu Lin, > > Your patch below looks suspiciously like the double-checked locking > anti-pattern, and is not guaranteed to work. > There really isn't a way to safely lazily initialize without using > synchronized or volatile. > > -Yonik > http://incubator.apache.org/solr Solr, the open-source Lucene search > server > > On 5/9/06, yueyu lin <[EMAIL PROTECTED]> wrote: > > Yes, the modification is still synchronized and the first thread will be > > responsible for reading first. And then other threads will not read and > the > > synchronization is unnecessary. > > private void ensureIndexIsRead() throws IOException { > > if (indexTerms != null) // index already read > > return; // do nothing > > synchronized(this){ > > System.out.println("Read [EMAIL PROTECTED]@"); > > if(indexTerms != null){ > > System.out.println ("Someone read it.return-_-"); > > return ; > > } > > readIndex (); > > } > > } > > > > private synchronized void readIndex() throws IOException{ > > Term[] m_indexTerms = null; > > try { > > int indexSize = (int)indexEnum.size; // otherwise read > > index > > m_indexTerms = new Term[indexSize]; > > indexInfos = new TermInfo[indexSize]; > > indexPointers = new long[indexSize]; > > > > for (int i = 0; indexEnum.next(); i++) { > > m_indexTerms[i] = indexEnum.term(); > > indexInfos[i] = indexEnum.termInfo(); > > indexPointers[i] = indexEnum.indexPointer; > > } > > } finally { > > indexEnum.close(); > > indexEnum = null; > > indexTerms = m_indexTerms; > > } > > } > > > > That's a small trick I learned when I was developing a busy stock > system. > > > > If the method ensureIndexIsRead() is synchronized, it will be blocked > for a > > while, although even 2 lines codes. > > --------------------------------------------------------------------- > To unsubscribe, e-mail: [EMAIL PROTECTED] > For additional commands, e-mail: [EMAIL PROTECTED] > > -- -- Yueyu Lin
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