eleveldb/c_src/refobjects.cc at develop · basho/eleveldb · GitHub

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// -------------------------------------------------------------------

// eleveldb: Erlang Wrapper for LevelDB (http://code.google.com/p/leveldb/)

// This file is provided to you under the Apache License,

// Version 2.0 (the "License"); you may not use this file

// except in compliance with the License. You may obtain

// a copy of the License at

// http://www.apache.org/licenses/LICENSE-2.0

// Unless required by applicable law or agreed to in writing,

// software distributed under the License is distributed on an

// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY

// KIND, either express or implied. See the License for the

// specific language governing permissions and limitations

// under the License.

// -------------------------------------------------------------------

#ifndef INCL_REFOBJECTS_H

#include "refobjects.h"

#endif

#ifndef INCL_WORKITEMS_H

#include "workitems.h"

#endif

#include "leveldb/atomics.h"

#include "leveldb/cache.h"

#include "leveldb/filter_policy.h"

namespace eleveldb {

/**

* RefObject Functions

RefObject::RefObject()

{

leveldb::gPerfCounters->Inc(leveldb::ePerfElevelRefCreate);

} // RefObject::RefObject

RefObject::~RefObject()

{

leveldb::gPerfCounters->Inc(leveldb::ePerfElevelRefDelete);

} // RefObject::~RefObject

/**

* Erlang reference object

ErlRefObject::ErlRefObject()

: m_ErlangThisPtr(NULL),

m_CloseMutex(true), // true => creates a mutex that can be locked recursively

m_CloseCond(&m_CloseMutex), m_CloseRequested(0)

{

} // ErlRefObject::ErlRefObject

ErlRefObject::~ErlRefObject()

{

} // ErlRefObject::~ErlRefObject

bool

ErlRefObject::ClaimCloseFromCThread()

{

bool ret_flag;

void * volatile * erlang_ptr;

ret_flag=false;

// first C thread claims contents of m_ErlangThisPtr and sets it to NULL

// This reduces number of times C code might look into Erlang heap memory

// that has garbage collected

erlang_ptr=m_ErlangThisPtr;

if (leveldb::compare_and_swap((void**)&m_ErlangThisPtr, (void *)erlang_ptr, (void *)NULL)

&& NULL!=erlang_ptr)

{

// now test if this C thread preceded Erlang in claiming the close operation

ret_flag=leveldb::compare_and_swap((void **)erlang_ptr, (void *)this,(void *) NULL);

} // if

return(ret_flag);

} // ErlRefObject::ClaimCloseFromCThread

void

ErlRefObject::InitiateCloseRequest()

{

m_CloseRequested=1;

Shutdown();

// WAIT for shutdown to complete

{

leveldb::MutexLock lock(&m_CloseMutex);

// one ref from construction, one ref from broadcast in RefDec below

// (only wait if RefDec has not signaled)

if (1<GetRefCount() && 1==GetCloseRequested())

{

m_CloseCond.Wait();

}

} // unlock m_CloseMutex

m_CloseRequested=3;

RefDec();

return;

} // ErlRefObject::InitiateCloseRequest

uint32_t

ErlRefObject::RefDec()

{

uint32_t cur_count;

{

leveldb::MutexLock lock(&m_CloseMutex);

cur_count=RefObject::RefDecNoDelete();

if (cur_count<2 && 1==GetCloseRequested())

{

bool flag;

// state 2 is sign that all secondary references have cleared

m_CloseRequested=2;

// is there really more than one ref count now?

flag=(0<GetRefCount());

if (flag)

{

RefObject::RefInc();

m_CloseCond.SignalAll();

} // if

// this "flag" and ref count dance is to ensure

// that the mutex unlock is called on all threads

// before destruction.

if (flag)

RefObject::RefDecNoDelete();

else

cur_count=0;

} // if

} // unlock m_CloseMutex

if (0==cur_count)

{

// the following assert is a mining canary for double

// delete of object. Seen twice since 2013. Likely

// due to second RefDecNoDelete() call above having been RefDec()

assert(0!=GetCloseRequested());

delete this;

} // if

return(cur_count);

} // ErlRefObject::RefDec

/**

* DbObject Functions

ErlNifResourceType * DbObject::m_Db_RESOURCE(NULL);

void

DbObject::CreateDbObjectType(

ErlNifEnv * Env)

{

ErlNifResourceFlags flags = (ErlNifResourceFlags)(ERL_NIF_RT_CREATE | ERL_NIF_RT_TAKEOVER);

m_Db_RESOURCE = enif_open_resource_type(Env, NULL, "eleveldb_DbObject",

&DbObject::DbObjectResourceCleanup,

flags, NULL);

return;

} // DbObject::CreateDbObjectType

void *

DbObject::CreateDbObject(

leveldb::DB * Db,

leveldb::Options * DbOptions)

{

DbObject * ret_ptr;

void * alloc_ptr;

// the alloc call initializes the reference count to "one"

alloc_ptr=enif_alloc_resource(m_Db_RESOURCE, sizeof(DbObject *));

ret_ptr=new DbObject(Db, DbOptions);

*(DbObject **)alloc_ptr=ret_ptr;

// manual reference increase to keep active until "eleveldb_close" called

ret_ptr->RefInc();

ret_ptr->m_ErlangThisPtr=(void * volatile *)alloc_ptr;

return(alloc_ptr);

} // DbObject::CreateDbObject

DbObject *

DbObject::RetrieveDbObject(

ErlNifEnv * Env,

const ERL_NIF_TERM & DbTerm,

bool * term_ok)

{

DbObject ** db_ptr_ptr, * ret_ptr;

ret_ptr=NULL;

if (NULL!=term_ok)

{

*term_ok=false;

}

if (NULL!=term_ok)

*term_ok=false;

if (enif_get_resource(Env, DbTerm, m_Db_RESOURCE, (void **)&db_ptr_ptr))

{

if (NULL!=term_ok)

*term_ok=true;

ret_ptr=*db_ptr_ptr;

if (NULL!=ret_ptr)

{

// has close been requested?

if (0!=ret_ptr->GetCloseRequested())

{

// object already closing

ret_ptr=NULL;

} // if

return(ret_ptr);

} // DbObject::RetrieveDbObject

void

DbObject::DbObjectResourceCleanup(

ErlNifEnv * Env,

void * Arg)

{

DbObject * volatile * erl_ptr;

DbObject * db_ptr;

erl_ptr=(DbObject * volatile *)Arg;

db_ptr=*erl_ptr;

// is Erlang first to initiate close?

if (leveldb::compare_and_swap(erl_ptr, db_ptr, (DbObject *)NULL)

&& NULL!=db_ptr)

{

db_ptr->InitiateCloseRequest();

} // if

return;

} // DbObject::DbObjectResourceCleanup

DbObject::DbObject(

leveldb::DB * DbPtr,

leveldb::Options * Options)

: m_Db(DbPtr), m_DbOptions(Options)

{

} // DbObject::DbObject

// iterators should already be cleared since they hold a reference

DbObject::~DbObject()

{

// close the db

delete m_Db;

m_Db=NULL;

if (NULL!=m_DbOptions)

{

// Release any cache we explicitly allocated when setting up options

delete m_DbOptions->block_cache;

m_DbOptions->block_cache = NULL;

// Clean up any filter policies

delete m_DbOptions->filter_policy;

m_DbOptions->filter_policy = NULL;

delete m_DbOptions;

m_DbOptions = NULL;

} // if

return;

} // DbObject::~DbObject

void

DbObject::Shutdown()

{

bool again;

ItrObject * itr_ptr;

{

again=false;

itr_ptr=NULL;

// lock the ItrList

{

leveldb::MutexLock lock(&m_ItrMutex);

if (!m_ItrList.empty())

{

again=true;

itr_ptr=m_ItrList.front();

m_ItrList.pop_front();

} // if

}

// must be outside lock so ItrObject can attempt

// RemoveReference

if (again)

{

// follow protocol, only one thread calls Initiate

// if (leveldb::compare_and_swap(itr_ptr->m_ErlangThisPtr, itr_ptr, (ItrObject *)NULL))

if (itr_ptr->ClaimCloseFromCThread())

{

itr_ptr->ItrObject::InitiateCloseRequest();

} // if

} while(again);

return;

} // DbObject::Shutdown

bool

DbObject::AddReference(

ItrObject * ItrPtr)

{

bool ret_flag;

leveldb::MutexLock lock(&m_ItrMutex);

ret_flag=(0==GetCloseRequested());

if (ret_flag)

m_ItrList.push_back(ItrPtr);

return(ret_flag);

} // DbObject::AddReference

void

DbObject::RemoveReference(

ItrObject * ItrPtr)

{

leveldb::MutexLock lock(&m_ItrMutex);

m_ItrList.remove(ItrPtr);

return;

} // DbObject::RemoveReference

/**

* Regenerative iterator object (malloc memory)

LevelIteratorWrapper::LevelIteratorWrapper(

DbObjectPtr_t & DbPtr, //!< db access for local iterator rebuild

leveldb::ReadOptions & Options) //!< options to use in iterator rebuild

: m_DbPtr(DbPtr), m_Options(Options),

m_Snapshot(NULL), m_Iterator(NULL),

m_HandoffAtomic(0), m_PrefetchStarted(false),

m_IteratorStale(0), m_StillUse(true),

m_IsValid(false)

{

RebuildIterator();

} // LevelIteratorWrapper::LevelIteratorWrapper

/**

* Iterator management object (Erlang memory)

ErlNifResourceType * ItrObject::m_Itr_RESOURCE(NULL);

void

ItrObject::CreateItrObjectType(

ErlNifEnv * Env)

{

ErlNifResourceFlags flags = (ErlNifResourceFlags)(ERL_NIF_RT_CREATE | ERL_NIF_RT_TAKEOVER);

m_Itr_RESOURCE = enif_open_resource_type(Env, NULL, "eleveldb_ItrObject",

&ItrObject::ItrObjectResourceCleanup,

flags, NULL);

return;

} // ItrObject::CreateItrObjectType

void *

ItrObject::CreateItrObject(

DbObjectPtr_t & DbPtr,

bool KeysOnly,

leveldb::ReadOptions & Options)

{

ItrObjErlang * erl_ptr;

ItrObject * ret_ptr;

void * alloc_ptr;

// the alloc call initializes the reference count to "one"

alloc_ptr=enif_alloc_resource(m_Itr_RESOURCE, sizeof(ItrObjErlang));

erl_ptr=(ItrObjErlang *)alloc_ptr;

ret_ptr=new ItrObject(DbPtr, KeysOnly, Options);

erl_ptr->m_ItrPtr=ret_ptr;

erl_ptr->m_SpinLock=0;

// manual reference increase to keep active until "eleveldb_iterator_close" called

ret_ptr->RefInc();

ret_ptr->m_ErlangThisPtr=(void * volatile *)alloc_ptr;

return(alloc_ptr);

} // ItrObject::CreateItrObject

ItrObject *

ItrObject::RetrieveItrObject(

ErlNifEnv * Env,

const ERL_NIF_TERM & ItrTerm,

bool ItrClosing,

ItrObjectPtr_t & counted_ptr)

{

ItrObjErlang * erl_ptr;

ItrObject * ret_ptr;

ret_ptr=NULL;

if (enif_get_resource(Env, ItrTerm, m_Itr_RESOURCE, (void **)&erl_ptr))

{

ret_ptr=erl_ptr->m_ItrPtr;

// only continue if close sequence not started

if (NULL!=ret_ptr)

{

// need to use "const int" instead of literals for

// solaris and smartos compare_and_swap to compile

const int zero(0), one(1);

// lock access ... spin

while(!leveldb::compare_and_swap(&erl_ptr->m_SpinLock, zero, one)) ;

// has close been requested?

if (ret_ptr->GetCloseRequested()

|| (!ItrClosing && ret_ptr->m_DbPtr->GetCloseRequested()))

{

// object already closing

ret_ptr=NULL;

} // if

// set during spin lock

counted_ptr.assign(ret_ptr);

// use cas for memory fencing, we own the lock

leveldb::compare_and_swap(&erl_ptr->m_SpinLock, one, zero);

} // if

return(ret_ptr);

} // ItrObject::RetrieveItrObject

void

ItrObject::ItrObjectResourceCleanup(

ErlNifEnv * Env,

void * Arg)

{

ItrObjErlang * erl_ptr;

ItrObject * itr_ptr;

erl_ptr=(ItrObjErlang *)Arg;

itr_ptr=erl_ptr->m_ItrPtr;

// is Erlang first to initiate close?

if (leveldb::compare_and_swap(&erl_ptr->m_ItrPtr, itr_ptr, (ItrObject *)NULL)

&& NULL!=itr_ptr)

{

leveldb::gPerfCounters->Inc(leveldb::ePerfDebug3);

itr_ptr->InitiateCloseRequest();

} // if

return;

} // ItrObject::ItrObjectResourceCleanup

ItrObject::ItrObject(

DbObjectPtr_t & DbPtr,

bool KeysOnly,

leveldb::ReadOptions & Options)

: keys_only(KeysOnly), m_ReadOptions(Options),

m_Wrap(DbPtr, m_ReadOptions),

reuse_move(NULL),

m_DbPtr(DbPtr), itr_ref_env(NULL)

{

if (NULL!=DbPtr.get())

DbPtr->AddReference(this);

} // ItrObject::ItrObject

ItrObject::~ItrObject()

{

// not likely to have active reuse item since it would

// block destruction

ReleaseReuseMove();

if (NULL!=itr_ref_env)

{

enif_free_env(itr_ref_env);

itr_ref_env=NULL;

} // if

if (NULL!=m_DbPtr.get())

m_DbPtr->RemoveReference(this);

// do not clean up m_CloseMutex and m_CloseCond

return;

} // ItrObject::~ItrObject

/**

* matthewv - This is a hack to compensate for Riak AAE

* having two active processes using the same iterator.

* One process attempts a close while the other iterates along.

* This is to help the close succeed. (October 2016)

uint32_t

ItrObject::RefDec()

{

uint32_t cur_count;

// Race condition:

// Thread trying to close gets into InitiateCloseRequest() and

// finishes call to Shutdown(). Thread iterating gets far enough

// into async_iterator_move() to not see GetCloseRequest() set, but

// is able to create a new MoveItem within reuse_move.

// This hack knows that async_iterator_move() uses ItrObjectPtr_t that

// holds "this" until the end of the function. ItrObjectPtr_t will

// call RefDec in its destructor. Gives a chance to cleanup a tad.

if (1==GetCloseRequested())

ReleaseReuseMove();

// WARNING: the following call could delete this object.

// make no references to object members afterward

cur_count=ErlRefObject::RefDec();

return(cur_count);

} // ItrObject::RefDec

void

ItrObject::Shutdown()

{

// if there is an active move object, set it up to delete

// (reuse_move holds a counter to this object, which will

// release when move object destructs)

ReleaseReuseMove();

return;

} // ItrObject::Shutdown

bool

ItrObject::ReleaseReuseMove()

{

MoveTask * ptr;

// move pointer off ItrObject first, then decrement ...

// otherwise there is potential for infinite loop

ptr=(MoveTask *)reuse_move;

if (leveldb::compare_and_swap(&reuse_move, ptr, (MoveTask *)NULL)

&& NULL!=ptr)

{

ptr->RefDec();

} // if

return(NULL!=ptr);

} // ItrObject::ReleaseReuseMove()

} // namespace eleveldb

eleveldb/c_src/refobjects.cc at develop · basho/eleveldb · GitHub

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