[XRay][compiler-rt] XRay Buffer Queue

Summary:
This implements a simple buffer queue to manage a pre-allocated queue of
fixed-sized buffers to hold XRay records. We need this to support
Flight Data Recorder (FDR) mode. We also implement this as a sub-library
first to allow for development before actually using it in an
implementation.

Some important properties of the buffer queue:

- Thread-safe enqueueing/dequeueing of fixed-size buffers.
- Pre-allocation of buffers at construction.

Reviewers: majnemer, rSerge, echristo

Subscribers: mehdi_amini, mgorny, llvm-commits

Differential Revision: https://reviews.llvm.org/D26232

llvm-svn: 287910

1 files changed, 65 insertions, 0 deletions

diff --git a/compiler-rt/lib/xray/xray_buffer_queue.cc b/compiler-rt/lib/xray/xray_buffer_queue.cc
new file mode 100644
index 00000000000..17878eb85de
--- /dev/null
+++ b/compiler-rt/lib/xray/xray_buffer_queue.cc
@@ -0,0 +1,65 @@
+//===-- 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 <cassert>
+#include <cstdlib>
+
+using namespace __xray;
+
+BufferQueue::BufferQueue(std::size_t B, std::size_t N)
+    : BufferSize(B), Buffers(N) {
+  for (auto &Buf : Buffers) {
+    void *Tmp = malloc(BufferSize);
+    Buf.Buffer = Tmp;
+    Buf.Size = B;
+    if (Tmp != 0)
+      OwnedBuffers.insert(Tmp);
+  }
+}
+
+std::error_code BufferQueue::getBuffer(Buffer &Buf) {
+  if (Finalizing.load(std::memory_order_acquire))
+    return std::make_error_code(std::errc::state_not_recoverable);
+  std::lock_guard<std::mutex> Guard(Mutex);
+  if (Buffers.empty())
+    return std::make_error_code(std::errc::not_enough_memory);
+  Buf = Buffers.front();
+  Buffers.pop_front();
+  return {};
+}
+
+std::error_code BufferQueue::releaseBuffer(Buffer &Buf) {
+  if (OwnedBuffers.count(Buf.Buffer) == 0)
+    return std::make_error_code(std::errc::argument_out_of_domain);
+  std::lock_guard<std::mutex> Guard(Mutex);
+  Buffers.push_back(Buf);
+  Buf.Buffer = nullptr;
+  Buf.Size = BufferSize;
+  return {};
+}
+
+std::error_code BufferQueue::finalize() {
+  if (Finalizing.exchange(true, std::memory_order_acq_rel))
+    return std::make_error_code(std::errc::state_not_recoverable);
+  return {};
+}
+
+BufferQueue::~BufferQueue() {
+  for (auto &Buf : Buffers) {
+    free(Buf.Buffer);
+    Buf.Buffer = nullptr;
+    Buf.Size = 0;
+  }
+}