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| //===-- xray_buffer_queue.cpp ----------------------------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// 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_atomic.h"
#include "sanitizer_common/sanitizer_common.h"
#include "sanitizer_common/sanitizer_libc.h"
#if !SANITIZER_FUCHSIA
#include "sanitizer_common/sanitizer_posix.h"
#endif
#include "xray_allocator.h"
#include "xray_defs.h"
#include <memory>
#include <sys/mman.h>
using namespace __xray;
namespace {
BufferQueue::ControlBlock *allocControlBlock(size_t Size, size_t Count) {
auto B =
allocateBuffer((sizeof(BufferQueue::ControlBlock) - 1) + (Size * Count));
return B == nullptr ? nullptr
: reinterpret_cast<BufferQueue::ControlBlock *>(B);
}
void deallocControlBlock(BufferQueue::ControlBlock *C, size_t Size,
size_t Count) {
deallocateBuffer(reinterpret_cast<unsigned char *>(C),
(sizeof(BufferQueue::ControlBlock) - 1) + (Size * Count));
}
void decRefCount(BufferQueue::ControlBlock *C, size_t Size, size_t Count) {
if (C == nullptr)
return;
if (atomic_fetch_sub(&C->RefCount, 1, memory_order_acq_rel) == 1)
deallocControlBlock(C, Size, Count);
}
void incRefCount(BufferQueue::ControlBlock *C) {
if (C == nullptr)
return;
atomic_fetch_add(&C->RefCount, 1, memory_order_acq_rel);
}
// We use a struct to ensure that we are allocating one atomic_uint64_t per
// cache line. This allows us to not worry about false-sharing among atomic
// objects being updated (constantly) by different threads.
struct ExtentsPadded {
union {
atomic_uint64_t Extents;
unsigned char Storage[kCacheLineSize];
};
};
constexpr size_t kExtentsSize = sizeof(ExtentsPadded);
} // namespace
BufferQueue::ErrorCode BufferQueue::init(size_t BS, size_t BC) {
SpinMutexLock Guard(&Mutex);
if (!finalizing())
return BufferQueue::ErrorCode::AlreadyInitialized;
cleanupBuffers();
bool Success = false;
BufferSize = BS;
BufferCount = BC;
BackingStore = allocControlBlock(BufferSize, BufferCount);
if (BackingStore == nullptr)
return BufferQueue::ErrorCode::NotEnoughMemory;
auto CleanupBackingStore = at_scope_exit([&, this] {
if (Success)
return;
deallocControlBlock(BackingStore, BufferSize, BufferCount);
BackingStore = nullptr;
});
// Initialize enough atomic_uint64_t instances, each
ExtentsBackingStore = allocControlBlock(kExtentsSize, BufferCount);
if (ExtentsBackingStore == nullptr)
return BufferQueue::ErrorCode::NotEnoughMemory;
auto CleanupExtentsBackingStore = at_scope_exit([&, this] {
if (Success)
return;
deallocControlBlock(ExtentsBackingStore, kExtentsSize, BufferCount);
ExtentsBackingStore = nullptr;
});
Buffers = initArray<BufferRep>(BufferCount);
if (Buffers == nullptr)
return BufferQueue::ErrorCode::NotEnoughMemory;
// At this point we increment the generation number to associate the buffers
// to the new generation.
atomic_fetch_add(&Generation, 1, memory_order_acq_rel);
// First, we initialize the refcount in the ControlBlock, which we treat as
// being at the start of the BackingStore pointer.
atomic_store(&BackingStore->RefCount, 1, memory_order_release);
atomic_store(&ExtentsBackingStore->RefCount, 1, memory_order_release);
// Then we initialise the individual buffers that sub-divide the whole backing
// store. Each buffer will start at the `Data` member of the ControlBlock, and
// will be offsets from these locations.
for (size_t i = 0; i < BufferCount; ++i) {
auto &T = Buffers[i];
auto &Buf = T.Buff;
auto *E = reinterpret_cast<ExtentsPadded *>(&ExtentsBackingStore->Data +
(kExtentsSize * i));
Buf.Extents = &E->Extents;
atomic_store(Buf.Extents, 0, memory_order_release);
Buf.Generation = generation();
Buf.Data = &BackingStore->Data + (BufferSize * i);
Buf.Size = BufferSize;
Buf.BackingStore = BackingStore;
Buf.ExtentsBackingStore = ExtentsBackingStore;
Buf.Count = BufferCount;
T.Used = false;
}
Next = Buffers;
First = Buffers;
LiveBuffers = 0;
atomic_store(&Finalizing, 0, memory_order_release);
Success = true;
return BufferQueue::ErrorCode::Ok;
}
BufferQueue::BufferQueue(size_t B, size_t N,
bool &Success) XRAY_NEVER_INSTRUMENT
: BufferSize(B),
BufferCount(N),
Mutex(),
Finalizing{1},
BackingStore(nullptr),
ExtentsBackingStore(nullptr),
Buffers(nullptr),
Next(Buffers),
First(Buffers),
LiveBuffers(0),
Generation{0} {
Success = init(B, N) == BufferQueue::ErrorCode::Ok;
}
BufferQueue::ErrorCode BufferQueue::getBuffer(Buffer &Buf) {
if (atomic_load(&Finalizing, memory_order_acquire))
return ErrorCode::QueueFinalizing;
BufferRep *B = nullptr;
{
SpinMutexLock Guard(&Mutex);
if (LiveBuffers == BufferCount)
return ErrorCode::NotEnoughMemory;
B = Next++;
if (Next == (Buffers + BufferCount))
Next = Buffers;
++LiveBuffers;
}
incRefCount(BackingStore);
incRefCount(ExtentsBackingStore);
Buf = B->Buff;
Buf.Generation = generation();
B->Used = true;
return ErrorCode::Ok;
}
BufferQueue::ErrorCode BufferQueue::releaseBuffer(Buffer &Buf) {
// Check whether the buffer being referred to is within the bounds of the
// backing store's range.
BufferRep *B = nullptr;
{
SpinMutexLock Guard(&Mutex);
if (Buf.Generation != generation() || LiveBuffers == 0) {
Buf = {};
decRefCount(Buf.BackingStore, Buf.Size, Buf.Count);
decRefCount(Buf.ExtentsBackingStore, kExtentsSize, Buf.Count);
return BufferQueue::ErrorCode::Ok;
}
if (Buf.Data < &BackingStore->Data ||
Buf.Data > &BackingStore->Data + (BufferCount * BufferSize))
return BufferQueue::ErrorCode::UnrecognizedBuffer;
--LiveBuffers;
B = First++;
if (First == (Buffers + BufferCount))
First = Buffers;
}
// Now that the buffer has been released, we mark it as "used".
B->Buff = Buf;
B->Used = true;
decRefCount(Buf.BackingStore, Buf.Size, Buf.Count);
decRefCount(Buf.ExtentsBackingStore, kExtentsSize, Buf.Count);
atomic_store(B->Buff.Extents, atomic_load(Buf.Extents, memory_order_acquire),
memory_order_release);
Buf = {};
return ErrorCode::Ok;
}
BufferQueue::ErrorCode BufferQueue::finalize() {
if (atomic_exchange(&Finalizing, 1, memory_order_acq_rel))
return ErrorCode::QueueFinalizing;
return ErrorCode::Ok;
}
void BufferQueue::cleanupBuffers() {
for (auto B = Buffers, E = Buffers + BufferCount; B != E; ++B)
B->~BufferRep();
deallocateBuffer(Buffers, BufferCount);
decRefCount(BackingStore, BufferSize, BufferCount);
decRefCount(ExtentsBackingStore, kExtentsSize, BufferCount);
BackingStore = nullptr;
ExtentsBackingStore = nullptr;
Buffers = nullptr;
BufferCount = 0;
BufferSize = 0;
}
BufferQueue::~BufferQueue() { cleanupBuffers(); }
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