Cleanup: fix most 'unused parameter' warnings

[thirdparty/squid.git] / src / MemStore.cc

/*
 * Copyright (C) 1996-2014 The Squid Software Foundation and contributors
 *
 * Squid software is distributed under GPLv2+ license and includes
 * contributions from numerous individuals and organizations.
 * Please see the COPYING and CONTRIBUTORS files for details.
 */

/* DEBUG: section 20    Memory Cache */

#include "squid.h"
#include "base/RunnersRegistry.h"
#include "CollapsedForwarding.h"
#include "HttpReply.h"
#include "ipc/mem/Page.h"
#include "ipc/mem/Pages.h"
#include "MemObject.h"
#include "MemStore.h"
#include "mime_header.h"
#include "SquidConfig.h"
#include "SquidMath.h"
#include "StoreStats.h"
#include "tools.h"

/// shared memory segment path to use for MemStore maps
static const SBuf MapLabel("cache_mem_map");
/// shared memory segment path to use for the free slices index
static const char *SpaceLabel = "cache_mem_space";
/// shared memory segment path to use for IDs of shared pages with slice data
static const char *ExtrasLabel = "cache_mem_ex";
// TODO: sync with Rock::SwapDir::*Path()

// We store free slot IDs (i.e., "space") as Page objects so that we can use
// Ipc::Mem::PageStack. Pages require pool IDs. The value here is not really
// used except for a positivity test. A unique value is handy for debugging.
static const uint32_t SpacePoolId = 510716;

MemStore::MemStore(): map(NULL), lastWritingSlice(-1)
{
}

MemStore::~MemStore()
{
    delete map;
}

void
MemStore::init()
{
    const int64_t entryLimit = EntryLimit();
    if (entryLimit <= 0)
        return; // no memory cache configured or a misconfiguration

    // check compatibility with the disk cache, if any
    if (Config.cacheSwap.n_configured > 0) {
        const int64_t diskMaxSize = Store::Root().maxObjectSize();
        const int64_t memMaxSize = maxObjectSize();
        if (diskMaxSize == -1) {
            debugs(20, DBG_IMPORTANT, "WARNING: disk-cache maximum object size "
                   "is unlimited but mem-cache maximum object size is " <<
                   memMaxSize / 1024.0 << " KB");
        } else if (diskMaxSize > memMaxSize) {
            debugs(20, DBG_IMPORTANT, "WARNING: disk-cache maximum object size "
                   "is too large for mem-cache: " <<
                   diskMaxSize / 1024.0 << " KB > " <<
                   memMaxSize / 1024.0 << " KB");
        }
    }

    freeSlots = shm_old(Ipc::Mem::PageStack)(SpaceLabel);
    extras = shm_old(Extras)(ExtrasLabel);

    Must(!map);
    map = new MemStoreMap(MapLabel);
    map->cleaner = this;
}

void
MemStore::getStats(StoreInfoStats &stats) const
{
    const size_t pageSize = Ipc::Mem::PageSize();

    stats.mem.shared = true;
    stats.mem.capacity =
        Ipc::Mem::PageLimit(Ipc::Mem::PageId::cachePage) * pageSize;
    stats.mem.size =
        Ipc::Mem::PageLevel(Ipc::Mem::PageId::cachePage) * pageSize;
    stats.mem.count = currentCount();
}

void
MemStore::stat(StoreEntry &e) const
{
    storeAppendPrintf(&e, "\n\nShared Memory Cache\n");

    storeAppendPrintf(&e, "Maximum Size: %.0f KB\n", maxSize()/1024.0);
    storeAppendPrintf(&e, "Current Size: %.2f KB %.2f%%\n",
                      currentSize() / 1024.0,
                      Math::doublePercent(currentSize(), maxSize()));

    if (map) {
        const int entryLimit = map->entryLimit();
        const int slotLimit = map->sliceLimit();
        storeAppendPrintf(&e, "Maximum entries: %9d\n", entryLimit);
        if (entryLimit > 0) {
            storeAppendPrintf(&e, "Current entries: %" PRId64 " %.2f%%\n",
                              currentCount(), (100.0 * currentCount() / entryLimit));
        }

        storeAppendPrintf(&e, "Maximum slots:   %9d\n", slotLimit);
        if (slotLimit > 0) {
            const unsigned int slotsFree =
                Ipc::Mem::PagesAvailable(Ipc::Mem::PageId::cachePage);
            if (slotsFree <= static_cast<const unsigned int>(slotLimit)) {
                const int usedSlots = slotLimit - static_cast<const int>(slotsFree);
                storeAppendPrintf(&e, "Used slots:      %9d %.2f%%\n",
                                  usedSlots, (100.0 * usedSlots / slotLimit));
            }

            if (slotLimit < 100) { // XXX: otherwise too expensive to count
                Ipc::ReadWriteLockStats stats;
                map->updateStats(stats);
                stats.dump(e);
            }
        }
    }
}

void
MemStore::maintain()
{
}

uint64_t
MemStore::minSize() const
{
    return 0; // XXX: irrelevant, but Store parent forces us to implement this
}

uint64_t
MemStore::maxSize() const
{
    return Config.memMaxSize;
}

uint64_t
MemStore::currentSize() const
{
    return Ipc::Mem::PageLevel(Ipc::Mem::PageId::cachePage) *
           Ipc::Mem::PageSize();
}

uint64_t
MemStore::currentCount() const
{
    return map ? map->entryCount() : 0;
}

int64_t
MemStore::maxObjectSize() const
{
    return min(Config.Store.maxInMemObjSize, Config.memMaxSize);
}

void
MemStore::reference(StoreEntry &)
{
}

bool
MemStore::dereference(StoreEntry &, bool)
{
    // no need to keep e in the global store_table for us; we have our own map
    return false;
}

int
MemStore::callback()
{
    return 0;
}

StoreSearch *
MemStore::search(String const, HttpRequest *)
{
    fatal("not implemented");
    return NULL;
}

StoreEntry *
MemStore::get(const cache_key *key)
{
    if (!map)
        return NULL;

    sfileno index;
    const Ipc::StoreMapAnchor *const slot = map->openForReading(key, index);
    if (!slot)
        return NULL;

    // create a brand new store entry and initialize it with stored info
    StoreEntry *e = new StoreEntry();

    // XXX: We do not know the URLs yet, only the key, but we need to parse and
    // store the response for the Root().get() callers to be happy because they
    // expect IN_MEMORY entries to already have the response headers and body.
    e->makeMemObject();

    anchorEntry(*e, index, *slot);

    const bool copied = copyFromShm(*e, index, *slot);

    if (copied) {
        e->hashInsert(key);
        return e;
    }

    debugs(20, 3, HERE << "mem-loading failed; freeing " << index);
    map->freeEntry(index); // do not let others into the same trap
    return NULL;
}

void
MemStore::get(String const, STOREGETCLIENT, void *)
{
    // XXX: not needed but Store parent forces us to implement this
    fatal("MemStore::get(key,callback,data) should not be called");
}

bool
MemStore::anchorCollapsed(StoreEntry &collapsed, bool &inSync)
{
    if (!map)
        return false;

    sfileno index;
    const Ipc::StoreMapAnchor *const slot = map->openForReading(
            reinterpret_cast<cache_key*>(collapsed.key), index);
    if (!slot)
        return false;

    anchorEntry(collapsed, index, *slot);
    inSync = updateCollapsedWith(collapsed, index, *slot);
    return true; // even if inSync is false
}

bool
MemStore::updateCollapsed(StoreEntry &collapsed)
{
    assert(collapsed.mem_obj);

    const sfileno index = collapsed.mem_obj->memCache.index;

    // already disconnected from the cache, no need to update
    if (index < 0)
        return true;

    if (!map)
        return false;

    const Ipc::StoreMapAnchor &anchor = map->readableEntry(index);
    return updateCollapsedWith(collapsed, index, anchor);
}

/// updates collapsed entry after its anchor has been located
bool
MemStore::updateCollapsedWith(StoreEntry &collapsed, const sfileno index, const Ipc::StoreMapAnchor &anchor)
{
    collapsed.swap_file_sz = anchor.basics.swap_file_sz;
    const bool copied = copyFromShm(collapsed, index, anchor);
    return copied;
}

/// anchors StoreEntry to an already locked map entry
void
MemStore::anchorEntry(StoreEntry &e, const sfileno index, const Ipc::StoreMapAnchor &anchor)
{
    const Ipc::StoreMapAnchor::Basics &basics = anchor.basics;

    e.swap_file_sz = basics.swap_file_sz;
    e.lastref = basics.lastref;
    e.timestamp = basics.timestamp;
    e.expires = basics.expires;
    e.lastmod = basics.lastmod;
    e.refcount = basics.refcount;
    e.flags = basics.flags;

    assert(e.mem_obj);
    if (anchor.complete()) {
        e.store_status = STORE_OK;
        e.mem_obj->object_sz = e.swap_file_sz;
        e.setMemStatus(IN_MEMORY);
    } else {
        e.store_status = STORE_PENDING;
        assert(e.mem_obj->object_sz < 0);
        e.setMemStatus(NOT_IN_MEMORY);
    }
    assert(e.swap_status == SWAPOUT_NONE); // set in StoreEntry constructor
    e.ping_status = PING_NONE;

    EBIT_CLR(e.flags, RELEASE_REQUEST);
    EBIT_CLR(e.flags, KEY_PRIVATE);
    EBIT_SET(e.flags, ENTRY_VALIDATED);

    MemObject::MemCache &mc = e.mem_obj->memCache;
    mc.index = index;
    mc.io = MemObject::ioReading;
}

/// copies the entire entry from shared to local memory
bool
MemStore::copyFromShm(StoreEntry &e, const sfileno index, const Ipc::StoreMapAnchor &anchor)
{
    debugs(20, 7, "mem-loading entry " << index << " from " << anchor.start);
    assert(e.mem_obj);

    // emulate the usual Store code but w/o inapplicable checks and callbacks:

    Ipc::StoreMapSliceId sid = anchor.start; // optimize: remember the last sid
    bool wasEof = anchor.complete() && sid < 0;
    int64_t sliceOffset = 0;
    while (sid >= 0) {
        const Ipc::StoreMapSlice &slice = map->readableSlice(index, sid);
        // slice state may change during copying; take snapshots now
        wasEof = anchor.complete() && slice.next < 0;
        const Ipc::StoreMapSlice::Size wasSize = slice.size;

        debugs(20, 9, "entry " << index << " slice " << sid << " eof " <<
               wasEof << " wasSize " << wasSize << " <= " <<
               anchor.basics.swap_file_sz << " sliceOffset " << sliceOffset <<
               " mem.endOffset " << e.mem_obj->endOffset());

        if (e.mem_obj->endOffset() < sliceOffset + wasSize) {
            // size of the slice data that we already copied
            const size_t prefixSize = e.mem_obj->endOffset() - sliceOffset;
            assert(prefixSize <= wasSize);

            const MemStoreMapExtras::Item &extra = extras->items[sid];

            char *page = static_cast<char*>(PagePointer(extra.page));
            const StoreIOBuffer sliceBuf(wasSize - prefixSize,
                                         e.mem_obj->endOffset(),
                                         page + prefixSize);
            if (!copyFromShmSlice(e, sliceBuf, wasEof))
                return false;
            debugs(20, 9, "entry " << index << " copied slice " << sid <<
                   " from " << extra.page << '+' << prefixSize);
        }
        // else skip a [possibly incomplete] slice that we copied earlier

        // careful: the slice may have grown _and_ gotten the next slice ID!
        if (slice.next >= 0) {
            assert(!wasEof);
            // here we know that slice.size may not change any more
            if (wasSize >= slice.size) { // did not grow since we started copying
                sliceOffset += wasSize;
                sid = slice.next;
            }
        } else if (wasSize >= slice.size) { // did not grow
            break;
        }
    }

    if (!wasEof) {
        debugs(20, 7, "mem-loaded " << e.mem_obj->endOffset() << '/' <<
               anchor.basics.swap_file_sz << " bytes of " << e);
        return true;
    }

    debugs(20, 7, "mem-loaded all " << e.mem_obj->object_sz << '/' <<
           anchor.basics.swap_file_sz << " bytes of " << e);

    // from StoreEntry::complete()
    e.mem_obj->object_sz = e.mem_obj->endOffset();
    e.store_status = STORE_OK;
    e.setMemStatus(IN_MEMORY);

    assert(e.mem_obj->object_sz >= 0);
    assert(static_cast<uint64_t>(e.mem_obj->object_sz) == anchor.basics.swap_file_sz);
    // would be nice to call validLength() here, but it needs e.key

    // we read the entire response into the local memory; no more need to lock
    disconnect(e);
    return true;
}

/// imports one shared memory slice into local memory
bool
MemStore::copyFromShmSlice(StoreEntry &e, const StoreIOBuffer &buf, bool eof)
{
    debugs(20, 7, "buf: " << buf.offset << " + " << buf.length);

    // from store_client::readBody()
    // parse headers if needed; they might span multiple slices!
    HttpReply *rep = (HttpReply *)e.getReply();
    if (rep->pstate < psParsed) {
        // XXX: have to copy because httpMsgParseStep() requires 0-termination
        MemBuf mb;
        mb.init(buf.length+1, buf.length+1);
        mb.append(buf.data, buf.length);
        mb.terminate();
        const int result = rep->httpMsgParseStep(mb.buf, buf.length, eof);
        if (result > 0) {
            assert(rep->pstate == psParsed);
            EBIT_CLR(e.flags, ENTRY_FWD_HDR_WAIT);
        } else if (result < 0) {
            debugs(20, DBG_IMPORTANT, "Corrupted mem-cached headers: " << e);
            return false;
        } else { // more slices are needed
            assert(!eof);
        }
    }
    debugs(20, 7, "rep pstate: " << rep->pstate);

    // local memory stores both headers and body so copy regardless of pstate
    const int64_t offBefore = e.mem_obj->endOffset();
    assert(e.mem_obj->data_hdr.write(buf)); // from MemObject::write()
    const int64_t offAfter = e.mem_obj->endOffset();
    // expect to write the entire buf because StoreEntry::write() never fails
    assert(offAfter >= 0 && offBefore <= offAfter &&
           static_cast<size_t>(offAfter - offBefore) == buf.length);
    return true;
}

/// whether we should cache the entry
bool
MemStore::shouldCache(StoreEntry &e) const
{
    if (e.mem_status == IN_MEMORY) {
        debugs(20, 5, "already loaded from mem-cache: " << e);
        return false;
    }

    if (e.mem_obj && e.mem_obj->memCache.offset > 0) {
        debugs(20, 5, "already written to mem-cache: " << e);
        return false;
    }

    if (!e.memoryCachable()) {
        debugs(20, 7, HERE << "Not memory cachable: " << e);
        return false; // will not cache due to entry state or properties
    }

    assert(e.mem_obj);

    if (e.mem_obj->vary_headers) {
        // XXX: We must store/load SerialisedMetaData to cache Vary in RAM
        debugs(20, 5, "Vary not yet supported: " << e.mem_obj->vary_headers);
        return false;
    }

    const int64_t expectedSize = e.mem_obj->expectedReplySize(); // may be < 0

    // objects of unknown size are not allowed into memory cache, for now
    if (expectedSize < 0) {
        debugs(20, 5, "Unknown expected size: " << e);
        return false;
    }

    const int64_t loadedSize = e.mem_obj->endOffset();
    const int64_t ramSize = max(loadedSize, expectedSize);

    if (ramSize > maxObjectSize()) {
        debugs(20, 5, HERE << "Too big max(" <<
               loadedSize << ", " << expectedSize << "): " << e);
        return false; // will not cache due to cachable entry size limits
    }

    if (!e.mem_obj->isContiguous()) {
        debugs(20, 5, "not contiguous");
        return false;
    }

    if (!map) {
        debugs(20, 5, HERE << "No map to mem-cache " << e);
        return false;
    }

    if (EBIT_TEST(e.flags, ENTRY_SPECIAL)) {
        debugs(20, 5, "Not mem-caching ENTRY_SPECIAL " << e);
        return false;
    }

    return true;
}

/// locks map anchor and preps to store the entry in shared memory
bool
MemStore::startCaching(StoreEntry &e)
{
    sfileno index = 0;
    Ipc::StoreMapAnchor *slot = map->openForWriting(reinterpret_cast<const cache_key *>(e.key), index);
    if (!slot) {
        debugs(20, 5, HERE << "No room in mem-cache map to index " << e);
        return false;
    }

    assert(e.mem_obj);
    e.mem_obj->memCache.index = index;
    e.mem_obj->memCache.io = MemObject::ioWriting;
    slot->set(e);
    map->startAppending(index);
    e.memOutDecision(true);
    return true;
}

/// copies all local data to shared memory
void
MemStore::copyToShm(StoreEntry &e)
{
    // prevents remote readers from getting ENTRY_FWD_HDR_WAIT entries and
    // not knowing when the wait is over
    if (EBIT_TEST(e.flags, ENTRY_FWD_HDR_WAIT)) {
        debugs(20, 5, "postponing copying " << e << " for ENTRY_FWD_HDR_WAIT");
        return;
    }

    assert(map);
    assert(e.mem_obj);

    const int32_t index = e.mem_obj->memCache.index;
    assert(index >= 0);
    Ipc::StoreMapAnchor &anchor = map->writeableEntry(index);

    const int64_t eSize = e.mem_obj->endOffset();
    if (e.mem_obj->memCache.offset >= eSize) {
        debugs(20, 5, "postponing copying " << e << " for lack of news: " <<
               e.mem_obj->memCache.offset << " >= " << eSize);
        return; // nothing to do (yet)
    }

    if (anchor.start < 0) { // must allocate the very first slot for e
        Ipc::Mem::PageId page;
        anchor.start = reserveSapForWriting(page); // throws
        extras->items[anchor.start].page = page;
    }

    lastWritingSlice = anchor.start;
    const size_t sliceCapacity = Ipc::Mem::PageSize();

    // fill, skip slices that are already full
    // Optimize: remember lastWritingSlice in e.mem_obj
    while (e.mem_obj->memCache.offset < eSize) {
        Ipc::StoreMap::Slice &slice =
            map->writeableSlice(e.mem_obj->memCache.index, lastWritingSlice);

        if (slice.size >= sliceCapacity) {
            if (slice.next >= 0) {
                lastWritingSlice = slice.next;
                continue;
            }

            Ipc::Mem::PageId page;
            slice.next = lastWritingSlice = reserveSapForWriting(page);
            extras->items[lastWritingSlice].page = page;
            debugs(20, 7, "entry " << index << " new slice: " << lastWritingSlice);
        }

        copyToShmSlice(e, anchor);
    }

    debugs(20, 7, "mem-cached available " << eSize << " bytes of " << e);
}

/// copies at most one slice worth of local memory to shared memory
void
MemStore::copyToShmSlice(StoreEntry &e, Ipc::StoreMapAnchor &anchor)
{
    Ipc::StoreMap::Slice &slice =
        map->writeableSlice(e.mem_obj->memCache.index, lastWritingSlice);

    Ipc::Mem::PageId page = extras->items[lastWritingSlice].page;
    assert(lastWritingSlice >= 0 && page);
    debugs(20, 7, "entry " << e << " slice " << lastWritingSlice << " has " <<
           page);

    const int64_t bufSize = Ipc::Mem::PageSize();
    const int64_t sliceOffset = e.mem_obj->memCache.offset % bufSize;
    StoreIOBuffer sharedSpace(bufSize - sliceOffset, e.mem_obj->memCache.offset,
                              static_cast<char*>(PagePointer(page)) + sliceOffset);

    // check that we kept everything or purge incomplete/sparse cached entry
    const ssize_t copied = e.mem_obj->data_hdr.copy(sharedSpace);
    if (copied <= 0) {
        debugs(20, 2, "Failed to mem-cache " << (bufSize - sliceOffset) <<
               " bytes of " << e << " from " << e.mem_obj->memCache.offset <<
               " in " << page);
        throw TexcHere("data_hdr.copy failure");
    }

    debugs(20, 7, "mem-cached " << copied << " bytes of " << e <<
           " from " << e.mem_obj->memCache.offset << " in " << page);

    slice.size += copied;
    e.mem_obj->memCache.offset += copied;
    anchor.basics.swap_file_sz = e.mem_obj->memCache.offset;
}

/// finds a slot and a free page to fill or throws
sfileno
MemStore::reserveSapForWriting(Ipc::Mem::PageId &page)
{
    Ipc::Mem::PageId slot;
    if (freeSlots->pop(slot)) {
        debugs(20, 5, "got a previously free slot: " << slot);

        if (Ipc::Mem::GetPage(Ipc::Mem::PageId::cachePage, page)) {
            debugs(20, 5, "and got a previously free page: " << page);
            return slot.number - 1;
        } else {
            debugs(20, 3, "but there is no free page, returning " << slot);
            freeSlots->push(slot);
        }
    }

    // catch free slots delivered to noteFreeMapSlice()
    assert(!waitingFor);
    waitingFor.slot = &slot;
    waitingFor.page = &page;
    if (map->purgeOne()) {
        assert(!waitingFor); // noteFreeMapSlice() should have cleared it
        assert(slot.set());
        assert(page.set());
        debugs(20, 5, "got previously busy " << slot << " and " << page);
        return slot.number - 1;
    }
    assert(waitingFor.slot == &slot && waitingFor.page == &page);
    waitingFor.slot = NULL;
    waitingFor.page = NULL;

    debugs(47, 3, "cannot get a slice; entries: " << map->entryCount());
    throw TexcHere("ran out of mem-cache slots");
}

void
MemStore::noteFreeMapSlice(const Ipc::StoreMapSliceId sliceId)
{
    Ipc::Mem::PageId &pageId = extras->items[sliceId].page;
    debugs(20, 9, "slice " << sliceId << " freed " << pageId);
    assert(pageId);
    Ipc::Mem::PageId slotId;
    slotId.pool = SpacePoolId;
    slotId.number = sliceId + 1;
    if (!waitingFor) {
        // must zero pageId before we give slice (and pageId extras!) to others
        Ipc::Mem::PutPage(pageId);
        freeSlots->push(slotId);
    } else {
        *waitingFor.slot = slotId;
        *waitingFor.page = pageId;
        waitingFor.slot = NULL;
        waitingFor.page = NULL;
        pageId = Ipc::Mem::PageId();
    }
}

void
MemStore::write(StoreEntry &e)
{
    assert(e.mem_obj);

    debugs(20, 7, "entry " << e);

    switch (e.mem_obj->memCache.io) {
    case MemObject::ioUndecided:
        if (!shouldCache(e) || !startCaching(e)) {
            e.mem_obj->memCache.io = MemObject::ioDone;
            e.memOutDecision(false);
            return;
        }
        break;

    case MemObject::ioDone:
    case MemObject::ioReading:
        return; // we should not write in all of the above cases

    case MemObject::ioWriting:
        break; // already decided to write and still writing
    }

    try {
        copyToShm(e);
        if (e.store_status == STORE_OK) // done receiving new content
            completeWriting(e);
        else
            CollapsedForwarding::Broadcast(e);
        return;
    } catch (const std::exception &x) { // TODO: should we catch ... as well?
        debugs(20, 2, "mem-caching error writing entry " << e << ": " << x.what());
        // fall through to the error handling code
    }

    disconnect(e);
}

void
MemStore::completeWriting(StoreEntry &e)
{
    assert(e.mem_obj);
    const int32_t index = e.mem_obj->memCache.index;
    assert(index >= 0);
    assert(map);

    debugs(20, 5, "mem-cached all " << e.mem_obj->memCache.offset << " bytes of " << e);

    e.mem_obj->memCache.index = -1;
    e.mem_obj->memCache.io = MemObject::ioDone;
    map->closeForWriting(index, false);

    CollapsedForwarding::Broadcast(e); // before we close our transient entry!
    Store::Root().transientsCompleteWriting(e);
}

void
MemStore::markForUnlink(StoreEntry &e)
{
    assert(e.mem_obj);
    if (e.mem_obj->memCache.index >= 0)
        map->freeEntry(e.mem_obj->memCache.index);
}

void
MemStore::unlink(StoreEntry &e)
{
    if (e.mem_obj && e.mem_obj->memCache.index >= 0) {
        map->freeEntry(e.mem_obj->memCache.index);
        disconnect(e);
    } else {
        // the entry may have been loaded and then disconnected from the cache
        map->freeEntryByKey(reinterpret_cast<cache_key*>(e.key));
    }

    e.destroyMemObject(); // XXX: but it may contain useful info such as a client list. The old code used to do that though, right?
}

void
MemStore::disconnect(StoreEntry &e)
{
    assert(e.mem_obj);
    MemObject &mem_obj = *e.mem_obj;
    if (mem_obj.memCache.index >= 0) {
        if (mem_obj.memCache.io == MemObject::ioWriting) {
            map->abortWriting(mem_obj.memCache.index);
            mem_obj.memCache.index = -1;
            mem_obj.memCache.io = MemObject::ioDone;
            Store::Root().transientsAbandon(e); // broadcasts after the change
        } else {
            assert(mem_obj.memCache.io == MemObject::ioReading);
            map->closeForReading(mem_obj.memCache.index);
            mem_obj.memCache.index = -1;
            mem_obj.memCache.io = MemObject::ioDone;
        }
    }
}

/// calculates maximum number of entries we need to store and map
int64_t
MemStore::EntryLimit()
{
    if (!Config.memShared || !Config.memMaxSize)
        return 0; // no memory cache configured

    const int64_t minEntrySize = Ipc::Mem::PageSize();
    const int64_t entryLimit = Config.memMaxSize / minEntrySize;
    return entryLimit;
}

/// reports our needs for shared memory pages to Ipc::Mem::Pages;
/// decides whether to use a shared memory cache or checks its configuration;
/// and initializes shared memory segments used by MemStore
class MemStoreRr: public Ipc::Mem::RegisteredRunner
{
public:
    /* RegisteredRunner API */
    MemStoreRr(): spaceOwner(NULL), mapOwner(NULL), extrasOwner(NULL) {}
    virtual void finalizeConfig();
    virtual void claimMemoryNeeds();
    virtual void useConfig();
    virtual ~MemStoreRr();

protected:
    /* Ipc::Mem::RegisteredRunner API */
    virtual void create();

private:
    Ipc::Mem::Owner<Ipc::Mem::PageStack> *spaceOwner; ///< free slices Owner
    MemStoreMap::Owner *mapOwner; ///< primary map Owner
    Ipc::Mem::Owner<MemStoreMapExtras> *extrasOwner; ///< PageIds Owner
};

RunnerRegistrationEntry(MemStoreRr);

void
MemStoreRr::claimMemoryNeeds()
{
    Ipc::Mem::NotePageNeed(Ipc::Mem::PageId::cachePage, MemStore::EntryLimit());
}

void
MemStoreRr::finalizeConfig()
{
    // decide whether to use a shared memory cache if the user did not specify
    if (!Config.memShared.configured()) {
        Config.memShared.configure(Ipc::Atomic::Enabled() &&
                                   Ipc::Mem::Segment::Enabled() && UsingSmp() &&
                                   Config.memMaxSize > 0);
    } else if (Config.memShared && !Ipc::Atomic::Enabled()) {
        // bail if the user wants shared memory cache but we cannot support it
        fatal("memory_cache_shared is on, but no support for atomic operations detected");
    } else if (Config.memShared && !Ipc::Mem::Segment::Enabled()) {
        fatal("memory_cache_shared is on, but no support for shared memory detected");
    } else if (Config.memShared && !UsingSmp()) {
        debugs(20, DBG_IMPORTANT, "WARNING: memory_cache_shared is on, but only"
               " a single worker is running");
    }
}

void
MemStoreRr::useConfig()
{
    assert(Config.memShared.configured());
    Ipc::Mem::RegisteredRunner::useConfig();
}

void
MemStoreRr::create()
{
    if (!Config.memShared)
        return;

    const int64_t entryLimit = MemStore::EntryLimit();
    if (entryLimit <= 0) {
        if (Config.memMaxSize > 0) {
            debugs(20, DBG_IMPORTANT, "WARNING: mem-cache size is too small ("
                   << (Config.memMaxSize / 1024.0) << " KB), should be >= " <<
                   (Ipc::Mem::PageSize() / 1024.0) << " KB");
        }
        return; // no memory cache configured or a misconfiguration
    }

    Must(!spaceOwner);
    spaceOwner = shm_new(Ipc::Mem::PageStack)(SpaceLabel, SpacePoolId,
                 entryLimit, 0);
    Must(!mapOwner);
    mapOwner = MemStoreMap::Init(MapLabel, entryLimit);
    Must(!extrasOwner);
    extrasOwner = shm_new(MemStoreMapExtras)(ExtrasLabel, entryLimit);
}

MemStoreRr::~MemStoreRr()
{
    delete extrasOwner;
    delete mapOwner;
    delete spaceOwner;
}