private LedgerEntryPage grabCleanPage(long ledger, long entry) throws IOException {
if (entry % entriesPerPage != 0) {
throw new IllegalArgumentException(entry + " is not a multiple of " + entriesPerPage);
}
while (true) {
boolean canAllocate = false;
if (pageCount.incrementAndGet() <= pageLimit) {
canAllocate = true;
} else {
pageCount.decrementAndGet();
}
if (canAllocate) {
LedgerEntryPage lep = new LedgerEntryPage(pageSize, entriesPerPage, pageMapAndList);
lep.setLedgerAndFirstEntry(ledger, entry);
lep.usePage();
return lep;
}
LedgerEntryPage lep = pageMapAndList.grabCleanPage(ledger, entry);
if (null != lep) {
return lep;
}
LOG.info(
"Could not grab a clean page for ledger {}, entry {}, force flushing dirty ledgers.",
ledger,
entry);
flushOneOrMoreLedgers(false);
}
}
/**
* 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;
}