/// <summary>
/// Allocate a new swapper id for the given <seealso cref="PageSwapper"/>.
/// </summary>
internal int Allocate(PageSwapper swapper)
{
lock (this)
{
SwapperMapping[] swapperMappings = this._swapperMappings;
// First look for an available freed slot.
lock ( _free )
{
if (!_free.Empty)
{
int id = _free.intIterator().next();
_free.remove(id);
swapperMappings[id] = new SwapperMapping(id, swapper);
this._swapperMappings = swapperMappings; // Volatile store synchronizes-with loads in getters.
return(id);
}
}
// No free slot was found above, so we extend the array to make room for a new slot.
int id = swapperMappings.Length;
if (id + 1 > _maxSwapperId)
{
throw new System.InvalidOperationException("All swapper ids are allocated: " + _maxSwapperId);
}
swapperMappings = Arrays.copyOf(swapperMappings, id + 1);
swapperMappings[id] = new SwapperMapping(id, swapper);
this._swapperMappings = swapperMappings; // Volatile store synchronizes-with loads in getters.
return(id);
}
}
/// <summary>
/// Get the <seealso cref="SwapperMapping"/> for the given swapper id.
/// </summary>
internal SwapperMapping GetAllocation(int id)
{
CheckId(id);
SwapperMapping swapperMapping = _swapperMappings[id];
if (swapperMapping == null || swapperMapping == _tombstone)
{
return(null);
}
return(swapperMapping);
}
/// <summary>
/// Collect all freed page swapper ids, and pass them to the given callback, after which the freed ids will be
/// eligible for reuse.
/// This is done with careful synchronisation such that allocating and freeing of ids is allowed to mostly proceed
/// concurrently.
/// </summary>
internal void Vacuum(System.Action <IntSet> evictAllLoadedPagesCallback)
{
// We do this complicated locking to avoid blocking allocate() and free() as much as possible, while still only
// allow a single thread to do vacuum at a time, and at the same time have consistent locking around the
// set of free ids.
lock ( _vacuumLock )
{
// Collect currently free ids.
//JAVA TO C# CONVERTER WARNING: The original Java variable was marked 'final':
//ORIGINAL LINE: final org.eclipse.collections.api.set.primitive.MutableIntSet freeIds = new org.eclipse.collections.impl.set.mutable.primitive.IntHashSet();
MutableIntSet freeIds = new IntHashSet();
SwapperMapping[] swapperMappings = this._swapperMappings;
for (int id = 0; id < swapperMappings.Length; id++)
{
SwapperMapping swapperMapping = swapperMappings[id];
if (swapperMapping == _tombstone)
{
freeIds.add(id);
}
}
// Evict all of them without holding up the lock on the free id set. This allows allocate() and free() to
// proceed concurrently with our eviction. This is safe because we know that the ids we are evicting cannot
// possibly be reused until we remove them from the free id set, which we won't do until after we've evicted
// all of their loaded pages.
evictAllLoadedPagesCallback(freeIds);
// Finally, all of the pages that remained in memory with an unmapped swapper id have been evicted. We can
// now safely allow those ids to be reused. Note, however, that free() might have been called while we were
// doing this, so we can't just free.clear() the set; no, we have to explicitly remove only those specific
// ids whose pages we evicted.
lock (this)
{
//JAVA TO C# CONVERTER WARNING: The original Java variable was marked 'final':
//ORIGINAL LINE: final org.eclipse.collections.api.iterator.IntIterator itr = freeIds.intIterator();
IntIterator itr = freeIds.intIterator();
while (itr.hasNext())
{
int freeId = itr.next();
swapperMappings[freeId] = null;
}
this._swapperMappings = swapperMappings; // Volatile store synchronizes-with loads in getters.
}
lock ( _free )
{
_free.addAll(freeIds);
}
}
}
/// <summary>
/// Free the given swapper id, and return {@code true} if it is time for a
/// <seealso cref="MuninnPageCache.vacuum(SwapperSet)"/>, otherwise it returns {@code false}.
/// </summary>
internal bool Free(int id)
{
lock (this)
{
CheckId(id);
SwapperMapping[] swapperMappings = this._swapperMappings;
SwapperMapping current = swapperMappings[id];
if (current == null || current == _tombstone)
{
throw new System.InvalidOperationException("PageSwapper allocation id " + id + " is currently not allocated. Likely a double free bug.");
}
swapperMappings[id] = _tombstone;
this._swapperMappings = swapperMappings; // Volatile store synchronizes-with loads in getters.
_freeCounter++;
if (_freeCounter == 20)
{
_freeCounter = 0;
return(true);
}
return(false);
}
}
