greenplumn CRefCount 源码
greenplumn CRefCount 代码
文件路径：/src/backend/gporca/libgpos/include/gpos/common/CRefCount.h
//---------------------------------------------------------------------------
// Greenplum Database
// Copyright (C) 2008 Greenplum, Inc.
//
// @filename:
// CRefCount.h
//
// @doc:
// Base class for reference counting in the optimizer;
// Ref-counting is single-threaded only;
// Enforces allocation on the heap, i.e. no deletion unless the
// count has really dropped to zero
//---------------------------------------------------------------------------
#ifndef GPOS_CRefCount_H
#define GPOS_CRefCount_H
#include "gpos/assert.h"
#include "gpos/common/CHeapObject.h"
#include "gpos/error/CException.h"
#include "gpos/task/ITask.h"
#include "gpos/types.h"
#include "gpos/utils.h"
// pattern used to mark deallocated memory, this must match
// GPOS_MEM_FREED_PATTERN_CHAR in CMemoryPool.h
#define GPOS_WIPED_MEM_PATTERN 0xCdCdCdCdCdCdCdCd
namespace gpos
{
//---------------------------------------------------------------------------
// @class:
// CRefCount
//
// @doc:
// Basic reference counting
//
//---------------------------------------------------------------------------
class CRefCount : public CHeapObject
{
private:
// reference counter -- first in class to be in sync with Check()
ULONG_PTR m_refs{1};
#ifdef GPOS_DEBUG
// sanity check to detect deleted memory
void
Check() const
{
// assert that first member of class has not been wiped
GPOS_ASSERT(m_refs != GPOS_WIPED_MEM_PATTERN);
}
#endif // GPOS_DEBUG
public:
CRefCount(const CRefCount &) = delete;
// ctor
CRefCount() = default;
// FIXME: should mark this noexcept in non-assert builds
// dtor
virtual ~CRefCount() noexcept(false)
{
// enforce strict ref-counting unless we're in a pending exception,
// e.g., a ctor has thrown
GPOS_ASSERT(nullptr == ITask::Self() ||
ITask::Self()->HasPendingExceptions() || 0 == m_refs);
}
// return ref-count
ULONG_PTR
RefCount() const
{
return m_refs;
}
// return true if calling object's destructor is allowed
virtual BOOL
Deletable() const
{
return true;
}
// count up
void
AddRef()
{
#ifdef GPOS_DEBUG
Check();
#endif // GPOS_DEBUG
m_refs++;
}
// count down
void
Release()
{
#ifdef GPOS_DEBUG
Check();
#endif // GPOS_DEBUG
m_refs--;
if (0 == m_refs)
{
if (!Deletable())
{
// restore ref-count
AddRef();
// deletion is not allowed
GPOS_RAISE(CException::ExmaSystem,
CException::ExmiInvalidDeletion);
}
GPOS_DELETE(this);
}
}
// safe version of Release -- handles NULL pointers
static void
SafeRelease(CRefCount *rc)
{
if (nullptr != rc)
{
rc->Release();
}
}
}; // class CRefCount
} // namespace gpos
#endif // !GPOS_CRefCount_H
// EOF
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