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//===-- 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_common.h"
#include "sanitizer_common/sanitizer_libc.h"
#include "sanitizer_common/sanitizer_posix.h"
#include <memory>
#include <sys/mman.h>
#ifndef MAP_NORESERVE
// no-op on NetBSD (at least), unsupported flag on FreeBSD
#define MAP_NORESERVE 0
#endif
using namespace __xray;
using namespace __sanitizer;
template <class T> static T *allocRaw(size_t N) {
// TODO: Report errors?
// We use MAP_NORESERVE on platforms where it's supported to ensure that the
// pages we're allocating for XRay never end up in pages that can be swapped
// in/out. We're doing this because for FDR mode, we want to ensure that
// writes to the buffers stay resident in memory to prevent XRay itself from
// causing swapping/thrashing.
//
// In the case when XRay pages cannot be swapped in/out or there's not enough
// RAM to back these pages, we're willing to cause a segmentation fault
// instead of introducing latency in the measurement. We assume here that
// there are enough pages that are swappable in/out outside of the buffers
// being used by FDR mode (which are bounded and configurable anyway) to allow
// us to keep using always-resident memory.
//
// TODO: Make this configurable?
void *A = reinterpret_cast<void *>(
internal_mmap(NULL, N * sizeof(T), PROT_WRITE | PROT_READ,
MAP_ANONYMOUS | MAP_PRIVATE | MAP_NORESERVE, -1, 0));
return (A == MAP_FAILED) ? nullptr : reinterpret_cast<T *>(A);
}
template <class T> static void deallocRaw(T *ptr, size_t N) {
// TODO: Report errors?
if (ptr != nullptr)
internal_munmap(ptr, N);
}
template <class T> static T *initArray(size_t N) {
auto A = allocRaw<T>(N);
if (A != nullptr)
while (N > 0)
new (A + (--N)) T();
return A;
}
BufferQueue::BufferQueue(size_t B, size_t N, bool &Success)
: BufferSize(B), Buffers(initArray<BufferQueue::BufferRep>(N)),
BufferCount(N), Finalizing{0}, OwnedBuffers(initArray<void *>(N)),
Next(Buffers), First(Buffers), LiveBuffers(0) {
if (Buffers == nullptr) {
Success = false;
return;
}
if (OwnedBuffers == nullptr) {
// Clean up the buffers we've already allocated.
for (auto B = Buffers, E = Buffers + BufferCount; B != E; ++B)
B->~BufferRep();
deallocRaw(Buffers, N);
Success = false;
return;
};
for (size_t i = 0; i < N; ++i) {
auto &T = Buffers[i];
void *Tmp = allocRaw<char>(BufferSize);
if (Tmp == nullptr) {
Success = false;
return;
}
auto *Extents = allocRaw<BufferExtents>(1);
if (Extents == nullptr) {
Success = false;
return;
}
auto &Buf = T.Buff;
Buf.Data = Tmp;
Buf.Size = B;
Buf.Extents = Extents;
OwnedBuffers[i] = Tmp;
}
Success = true;
}
BufferQueue::ErrorCode BufferQueue::getBuffer(Buffer &Buf) {
if (atomic_load(&Finalizing, memory_order_acquire))
return ErrorCode::QueueFinalizing;
SpinMutexLock Guard(&Mutex);
if (LiveBuffers == BufferCount)
return ErrorCode::NotEnoughMemory;
auto &T = *Next;
auto &B = T.Buff;
Buf = B;
T.Used = true;
++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.Data) {
Found = true;
break;
}
}
if (!Found)
return ErrorCode::UnrecognizedBuffer;
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.Data = nullptr;
Buf.Size = 0;
--LiveBuffers;
if (++First == (Buffers + BufferCount))
First = Buffers;
return ErrorCode::Ok;
}
BufferQueue::ErrorCode BufferQueue::finalize() {
if (atomic_exchange(&Finalizing, 1, 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;
deallocRaw(Buf.Data, Buf.Size);
deallocRaw(Buf.Extents, 1);
}
for (auto B = Buffers, E = Buffers + BufferCount; B != E; ++B)
B->~BufferRep();
deallocRaw(Buffers, BufferCount);
deallocRaw(OwnedBuffers, BufferCount);
}
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