lib/xray/xray_buffer_queue.cc

//===-- xray_buffer_queue.cc -----------------------------------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file is a part of XRay, a dynamic runtime instruementation system.
//
// Defines the interface for a buffer queue implementation.
//
//===----------------------------------------------------------------------===//
#include "xray_buffer_queue.h"
#include "sanitizer_common/sanitizer_allocator_internal.h"
#include "sanitizer_common/sanitizer_common.h"
#include "sanitizer_common/sanitizer_libc.h"

using namespace __xray;
using namespace __sanitizer;

BufferQueue::BufferQueue(size_t B, size_t N, bool &Success)
    : BufferSize(B),
      Buffers(new BufferRep[N]()),
      BufferCount(N),
      Finalizing{0},
      OwnedBuffers(new void *[N]()),
      Next(Buffers),
      First(Buffers),
      LiveBuffers(0) {
  for (size_t i = 0; i < N; ++i) {
    auto &T = Buffers[i];
    void *Tmp = InternalAlloc(BufferSize);
    if (Tmp == nullptr) {
      Success = false;
      return;
    }
    auto &Buf = T.Buff;
    Buf.Buffer = Tmp;
    Buf.Size = B;
    OwnedBuffers[i] = Tmp;
  }
  Success = true;
}

BufferQueue::ErrorCode BufferQueue::getBuffer(Buffer &Buf) {
  if (__sanitizer::atomic_load(&Finalizing, __sanitizer::memory_order_acquire))
    return ErrorCode::QueueFinalizing;
  __sanitizer::SpinMutexLock Guard(&Mutex);
  if (LiveBuffers == BufferCount) return ErrorCode::NotEnoughMemory;

  auto &T = *Next;
  auto &B = T.Buff;
  Buf = B;
  ++LiveBuffers;

  if (++Next == (Buffers + BufferCount)) Next = Buffers;

  return ErrorCode::Ok;
}

BufferQueue::ErrorCode BufferQueue::releaseBuffer(Buffer &Buf) {
  // Blitz through the buffers array to find the buffer.
  bool Found = false;
  for (auto I = OwnedBuffers, E = OwnedBuffers + BufferCount; I != E; ++I) {
    if (*I == Buf.Buffer) {
      Found = true;
      break;
    }
  }
  if (!Found) return ErrorCode::UnrecognizedBuffer;

  __sanitizer::SpinMutexLock Guard(&Mutex);

  // This points to a semantic bug, we really ought to not be releasing more
  // buffers than we actually get.
  if (LiveBuffers == 0) return ErrorCode::NotEnoughMemory;

  // Now that the buffer has been released, we mark it as "used".
  First->Buff = Buf;
  First->Used = true;
  Buf.Buffer = nullptr;
  Buf.Size = 0;
  --LiveBuffers;
  if (++First == (Buffers + BufferCount)) First = Buffers;

  return ErrorCode::Ok;
}

BufferQueue::ErrorCode BufferQueue::finalize() {
  if (__sanitizer::atomic_exchange(&Finalizing, 1,
                                   __sanitizer::memory_order_acq_rel))
    return ErrorCode::QueueFinalizing;
  return ErrorCode::Ok;
}

BufferQueue::~BufferQueue() {
  for (auto I = Buffers, E = Buffers + BufferCount; I != E; ++I) {
    auto &T = *I;
    auto &Buf = T.Buff;
    InternalFree(Buf.Buffer);
  }
  delete[] Buffers;
  delete[] OwnedBuffers;
}