/**
* Get a clean page and provision it for the specified ledger and firstEntry within the ledger
*
* @param ledgerId Ledger id
* @param firstEntry Id of the first entry in the page
* @returns LedgerEntryPage if present
*/
LedgerEntryPage grabCleanPage(long ledgerId, long firstEntry) {
LedgerEntryPage lep = null;
while (lruCleanPageMap.size() > 0) {
lep = null;
synchronized (lruCleanPageMap) {
Iterator<Map.Entry<EntryKey, LedgerEntryPage>> iterator =
lruCleanPageMap.entrySet().iterator();
Map.Entry<EntryKey, LedgerEntryPage> entry = null;
while (iterator.hasNext()) {
entry = iterator.next();
iterator.remove();
if (entry.getValue().isClean() && !entry.getValue().inUse()) {
lep = entry.getValue();
break;
}
}
if (null == lep) {
LOG.debug("Did not find eligible page in the first pass");
return null;
}
}
// We found a candidate page, lets see if we can reclaim it before its re-used
ConcurrentMap<Long, LedgerEntryPage> pageMap = pages.get(lep.getLedger());
// Remove from map only if nothing has changed since we checked this lep.
// Its possible for the ledger to have been deleted or the page to have already
// been reclaimed. The page map is the definitive source of information, if anything
// has changed we should leave this page along and continue iterating to find
// another suitable page.
if ((null != pageMap) && (pageMap.remove(lep.getFirstEntry(), lep))) {
if (!lep.isClean()) {
// Someone wrote to this page while we were reclaiming it.
pageMap.put(lep.getFirstEntry(), lep);
lep = null;
} else {
// Do some bookkeeping on the page table
pages.remove(lep.getLedger(), EMPTY_PAGE_MAP);
// We can now safely reset this lep and return it.
lep.usePage();
lep.zeroPage();
lep.setLedgerAndFirstEntry(ledgerId, firstEntry);
return lep;
}
} else {
lep = null;
}
}
return lep;
}
/**
* Add a LedgerEntryPage to the page map
*
* @param lep Ledger Entry Page object
*/
private LedgerEntryPage putPage(LedgerEntryPage lep) {
// Do a get here to avoid too many new ConcurrentHashMaps() as putIntoTable is called
// frequently.
ConcurrentMap<Long, LedgerEntryPage> map = pages.get(lep.getLedger());
if (null == map) {
ConcurrentMap<Long, LedgerEntryPage> mapToPut =
new ConcurrentHashMap<Long, LedgerEntryPage>();
map = pages.putIfAbsent(lep.getLedger(), mapToPut);
if (null == map) {
map = mapToPut;
}
}
LedgerEntryPage oldPage = map.putIfAbsent(lep.getFirstEntry(), lep);
if (null == oldPage) {
oldPage = lep;
// Also include this in the clean page map if it qualifies.
// Note: This is done for symmetry and correctness, however it should never
// get exercised since we shouldn't attempt a put without the page being in use
addToCleanPagesList(lep);
}
return oldPage;
}
void updatePage(LedgerEntryPage lep) throws IOException {
if (!lep.isClean()) {
throw new IOException("Trying to update a dirty page");
}
FileInfo fi = null;
try {
fi = getFileInfo(lep.getLedger(), null);
long pos = lep.getFirstEntryPosition();
if (pos >= fi.size()) {
lep.zeroPage();
} else {
lep.readPage(fi);
}
} finally {
if (fi != null) {
fi.release();
}
}
}