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// **********************************************************************
//
// Copyright (c) 2003-2015 ZeroC, Inc. All rights reserved.
//
// This copy of Ice is licensed to you under the terms described in the
// ICE_LICENSE file included in this distribution.
//
// **********************************************************************
#include <Evictor.h>
#include <IceUtil/IceUtil.h>
using namespace std;
using namespace IceUtil;
namespace
{
int cacheMisses = 0;
IceUtil::Mutex* globalMutex = 0;
class Init
{
public:
Init()
{
globalMutex = new IceUtil::Mutex;
}
~Init()
{
delete globalMutex;
globalMutex = 0;
}
};
Init init;
}
//
// EvictorCache
//
EvictorCache::EvictorCache(CurrentDatabase& currentDb) :
_currentDb(currentDb)
{
}
//
// Returns 0 if object is not found.
//
EvictorEntryPtr
EvictorCache::load(const Ice::Identity& itemId)
{
{
IceUtil::Mutex::Lock lock(*globalMutex);
cacheMisses++;
if(cacheMisses % 1000 == 0)
{
cout << cacheMisses << " cache misses" << endl;
}
}
//
// You can simulate more expensive cache-misses by adding a sleep here:
//
// ThreadControl::sleep(Time::milliSeconds(1));
//
// Use a const Database& to avoid starting a transaction (just an optimization).
//
const Database& cdb = _currentDb.get();
Database::const_iterator p = cdb.find(itemId.name);
if(p == cdb.end())
{
return 0;
}
else
{
return new EvictorEntry(new ItemI(_currentDb, p->second));
}
}
//
// Finish initializing the entry after it has been inserted in the
// Cache map, but before any other thread can find it.
//
// pinned() is called while IceUtil::Cache's internal mutex is locked,
// so we must be careful with lock acquisition order. For example we
// cannot acquire the Evictor mutex here, since we also call
// IceUtil::Cache with the Evictor mutex locked.
//
void
EvictorCache::pinned(const EvictorEntryPtr& entry, EvictorCache::Position cp)
{
entry->stale = false;
entry->cachePosition = cp;
}
//
// EvictorEntry
//
EvictorEntry::EvictorEntry(const ItemIPtr& item) :
servant(item),
useCount(-1),
stale(true)
{
}
//
// Evictor
//
Evictor::Evictor(CurrentDatabase& currentDb, int size) :
_cache(currentDb),
_queueSize(0),
_size(size)
{
}
Ice::ObjectPtr
Evictor::locate(const Ice::Current& current, Ice::LocalObjectPtr& cookie)
{
cookie = 0;
//
// Lookup the cookie (EvictorEntry) in the cache; this will call load()
// if the entry is not yet in there.
//
// If we get an entry that was just evicted (stale == true), we try again.
//
for(;;)
{
EvictorEntryPtr entry = _cache.pin(current.id);
if(entry == 0)
{
//
// Will raise ObjectNotExistException.
//
return 0;
}
else
{
{
//
// Lock _mutex when reading/writing useCount, stale and queuePosition.
//
Mutex::Lock lock(_mutex);
if(entry->stale)
{
//
// Another thread just evicted this entry; try again.
//
continue;
}
cookie = entry;
if(entry->useCount < 0)
{
entry->useCount = 0;
_queueSize++;
}
else
{
_queue.erase(entry->queuePosition);
}
_queue.push_front(entry);
entry->queuePosition = _queue.begin();
entry->useCount++;
}
}
//
// We have at least one useCount, and servant is immutable.
//
return entry->servant;
}
}
void
Evictor::finished(const Ice::Current& /*current*/, const Ice::ObjectPtr& /*servant*/,
const Ice::LocalObjectPtr& cookie)
{
if(cookie != 0)
{
Mutex::Lock lock(_mutex);
EvictorEntryPtr entry = EvictorEntryPtr::dynamicCast(cookie);
assert(entry != 0);
entry->useCount--;
assert(entry->useCount >= 0);
evict();
}
}
void
Evictor::deactivate(const string& /*category*/)
{
Mutex::Lock lock(_mutex);
_size = 0;
evict();
}
void
Evictor::evict()
{
//
// Called with _mutex locked; try to erase the excess entries.
//
EvictorQueue::reverse_iterator p = _queue.rbegin();
int toErase = (_queueSize - _size);
while(toErase > 0 && p != _queue.rend())
{
//
// Get the last unused element from the evictor queue.
//
while(p != _queue.rend() && (*p)->useCount != 0)
{
++p;
}
if(p != _queue.rend())
{
EvictorEntryPtr& entry = *p;
assert(!entry->stale);
entry->stale = true;
_cache.unpin(entry->cachePosition);
//
// Erase returns a normal iterator to the item after the erased item;
// and then reverse_iterator() makes q point to the item before it.
//
p = EvictorQueue::reverse_iterator(_queue.erase(entry->queuePosition));
toErase--;
_queueSize--;
}
}
}
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