stdlib/public/runtime/RefCount.cpp

//===--- RefCount.cpp -----------------------------------------------------===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See https://swift.org/LICENSE.txt for license information
// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//

#include "swift/Runtime/HeapObject.h"

namespace swift {

template <typename RefCountBits>
void RefCounts<RefCountBits>::incrementSlow(RefCountBits oldbits,
                                            uint32_t n) {
  if (oldbits.hasSideTable()) {
    // Out-of-line slow path.
    auto side = oldbits.getSideTable();
    side->incrementStrong(n);
  }
  else {
    // Retain count overflow.
    swift::swift_abortRetainOverflow();
  }
}
template void RefCounts<InlineRefCountBits>::incrementSlow(InlineRefCountBits oldbits, uint32_t n);
template void RefCounts<SideTableRefCountBits>::incrementSlow(SideTableRefCountBits oldbits, uint32_t n);

template <typename RefCountBits>
void RefCounts<RefCountBits>::incrementNonAtomicSlow(RefCountBits oldbits,
                                                     uint32_t n) {
  if (oldbits.hasSideTable()) {
    // Out-of-line slow path.
    auto side = oldbits.getSideTable();
    side->incrementStrong(n);  // FIXME: can there be a nonatomic impl?
  } else {
    swift::swift_abortRetainOverflow();
  }
}
template void RefCounts<InlineRefCountBits>::incrementNonAtomicSlow(InlineRefCountBits oldbits, uint32_t n);
template void RefCounts<SideTableRefCountBits>::incrementNonAtomicSlow(SideTableRefCountBits oldbits, uint32_t n);

template <typename RefCountBits>
bool RefCounts<RefCountBits>::tryIncrementSlow(RefCountBits oldbits) {
  if (oldbits.hasSideTable())
    return oldbits.getSideTable()->tryIncrement();
  else
    swift::swift_abortRetainOverflow();
}
template bool RefCounts<InlineRefCountBits>::tryIncrementSlow(InlineRefCountBits oldbits);
template bool RefCounts<SideTableRefCountBits>::tryIncrementSlow(SideTableRefCountBits oldbits);

template <typename RefCountBits>
bool RefCounts<RefCountBits>::tryIncrementNonAtomicSlow(RefCountBits oldbits) {
  if (oldbits.hasSideTable())
    return oldbits.getSideTable()->tryIncrementNonAtomic();
  else
    swift::swift_abortRetainOverflow();
}
template bool RefCounts<InlineRefCountBits>::tryIncrementNonAtomicSlow(InlineRefCountBits oldbits);
template bool RefCounts<SideTableRefCountBits>::tryIncrementNonAtomicSlow(SideTableRefCountBits oldbits);

template <typename RefCountBits>
bool RefCounts<RefCountBits>::tryIncrementAndPinSlow(RefCountBits oldbits) {
  if (oldbits.hasSideTable())
    return oldbits.getSideTable()->tryIncrementAndPin();
  else
    swift::swift_abortRetainOverflow();
}
template bool RefCounts<InlineRefCountBits>::tryIncrementAndPinSlow(InlineRefCountBits oldbits);
template bool RefCounts<SideTableRefCountBits>::tryIncrementAndPinSlow(SideTableRefCountBits oldbits);

template <typename RefCountBits>
bool RefCounts<RefCountBits>::tryIncrementAndPinNonAtomicSlow(RefCountBits oldbits) {
  if (oldbits.hasSideTable())
    return oldbits.getSideTable()->tryIncrementAndPinNonAtomic();
  else
    swift::swift_abortRetainOverflow();
}
template bool RefCounts<InlineRefCountBits>::tryIncrementAndPinNonAtomicSlow(InlineRefCountBits oldbits);
template bool RefCounts<SideTableRefCountBits>::tryIncrementAndPinNonAtomicSlow(SideTableRefCountBits oldbits);


// Return an object's side table, allocating it if necessary.
// Returns null if the object is deiniting.
// SideTableRefCountBits specialization intentionally does not exist.
template <>
HeapObjectSideTableEntry* RefCounts<InlineRefCountBits>::allocateSideTable()
{
  auto oldbits = refCounts.load(SWIFT_MEMORY_ORDER_CONSUME);
  
  // Preflight failures before allocating a new side table.
  if (oldbits.hasSideTable()) {
    // Already have a side table. Return it.
    return oldbits.getSideTable();
  } 
  else if (oldbits.getIsDeiniting()) {
    // Already past the start of deinit. Do nothing.
    return nullptr;
  }

  // Preflight passed. Allocate a side table.
  
  // FIXME: custom side table allocator
  HeapObjectSideTableEntry *side = new HeapObjectSideTableEntry(getHeapObject());
  
  auto newbits = InlineRefCountBits(side);
  
  do {
    if (oldbits.hasSideTable()) {
      // Already have a side table. Return it and delete ours.
      // Read before delete to streamline barriers.
      auto result = oldbits.getSideTable();
      delete side;
      return result;
    }
    else if (oldbits.getIsDeiniting()) {
      // Already past the start of deinit. Do nothing.
      return nullptr;
    }
    
    side->initRefCounts(oldbits);
    
  } while (! refCounts.compare_exchange_weak(oldbits, newbits,
                                             std::memory_order_release,
                                             std::memory_order_relaxed));
  return side;
}


// SideTableRefCountBits specialization intentionally does not exist.
template <>
HeapObjectSideTableEntry* RefCounts<InlineRefCountBits>::formWeakReference()
{
  auto side = allocateSideTable();
  if (side)
    return side->incrementWeak();
  else
    return nullptr;
}

// namespace swift
}