[XRay][compiler-rt] Use a hand-written circular buffer in BufferQueue

Summary:
This change removes the dependency on using a std::deque<...> for the
storage of the buffers in the buffer queue. We instead implement a
fixed-size circular buffer that's resilient to exhaustion, and preserves
the semantics of the BufferQueue.

We're moving away from using std::deque<...> for two reasons:

  - We want to remove dependencies on the STL for data structures.

  - We want the data structure we use to not require re-allocation in
    the normal course of operation.

The internal implementation of the buffer queue uses heap-allocated
arrays that are initialized once when the BufferQueue is created, and
re-uses slots in the buffer array as buffers are returned in order.

We also change the lock used in the implementation to a spinlock
instead of a blocking mutex. We reason that since the release operations
now take very little time in the critical section, that a spinlock would
be appropriate.

This change is related to D38073.

This change is a re-submit with the following changes:

  - Keeping track of the live buffers with a counter independent of the
    pointers keeping track of the extents of the circular buffer.

  - Additional documentation of what the data members are meant to
    represent.

Reviewers: dblaikie, kpw, pelikan

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D38119

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk@314877 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 37 insertions, 11 deletions

diff --git a/test/xray/TestCases/Linux/fdr-thread-order.cc b/test/xray/TestCases/Linux/fdr-thread-order.cc
index 6ac2114a5..8e8c421dc 100644
--- a/test/xray/TestCases/Linux/fdr-thread-order.cc
+++ b/test/xray/TestCases/Linux/fdr-thread-order.cc
@@ -1,37 +1,63 @@
 // RUN: %clangxx_xray -g -std=c++11 %s -o %t
 // RUN: rm fdr-thread-order.* || true
-// RUN: XRAY_OPTIONS="patch_premain=false xray_naive_log=false xray_logfile_base=fdr-thread-order. xray_fdr_log=true verbosity=1 xray_fdr_log_func_duration_threshold_us=0" %run %t 2>&1 | FileCheck %s
-// RUN: %llvm_xray convert --symbolize --output-format=yaml -instr_map=%t "`ls fdr-thread-order.* | head -1`" | FileCheck %s --check-prefix TRACE
+// RUN: XRAY_OPTIONS="patch_premain=false xray_naive_log=false \
+// RUN:    xray_logfile_base=fdr-thread-order. xray_fdr_log=true verbosity=1 \
+// RUN:    xray_fdr_log_func_duration_threshold_us=0" %run %t 2>&1 | \
+// RUN:    FileCheck %s
+// RUN: %llvm_xray convert --symbolize --output-format=yaml -instr_map=%t \
+// RUN:    "`ls fdr-thread-order.* | head -1`"
+// RUN: %llvm_xray convert --symbolize --output-format=yaml -instr_map=%t \
+// RUN:    "`ls fdr-thread-order.* | head -1`" | \
+// RUN:    FileCheck %s --check-prefix TRACE
 // RUN: rm fdr-thread-order.*
 // FIXME: Make llvm-xray work on non-x86_64 as well.
 // REQUIRES: x86_64-linux
 // REQUIRES: built-in-llvm-tree
 
 #include "xray/xray_log_interface.h"
-#include <thread>
+#include <atomic>
 #include <cassert>
+#include <thread>
 
 constexpr auto kBufferSize = 16384;
 constexpr auto kBufferMax = 10;
 
-thread_local uint64_t var = 0;
-[[clang::xray_always_instrument]] void __attribute__((noinline)) f1() { ++var; }
-[[clang::xray_always_instrument]] void __attribute__((noinline)) f2() { ++var; }
+std::atomic<uint64_t> var{0};
+
+[[clang::xray_always_instrument]] void __attribute__((noinline)) f1() {
+  for (auto i = 0; i < 1 << 20; ++i)
+    ++var;
+}
+
+[[clang::xray_always_instrument]] void __attribute__((noinline)) f2() {
+  for (auto i = 0; i < 1 << 20; ++i)
+    ++var;
+}
 
 int main(int argc, char *argv[]) {
   using namespace __xray;
   FDRLoggingOptions Options;
+  __xray_patch();
   assert(__xray_log_init(kBufferSize, kBufferMax, &Options,
                          sizeof(FDRLoggingOptions)) ==
          XRayLogInitStatus::XRAY_LOG_INITIALIZED);
-  __xray_patch();
-  std::thread t1([] { f1(); });
-  std::thread t2([] { f2(); });
-  t1.join();
-  t2.join();
+
+  std::atomic_thread_fence(std::memory_order_acq_rel);
+
+  {
+    std::thread t1([] { f1(); });
+    std::thread t2([] { f2(); });
+    t1.join();
+    t2.join();
+  }
+
+  std::atomic_thread_fence(std::memory_order_acq_rel);
   __xray_log_finalize();
   __xray_log_flushLog();
+  __xray_unpatch();
+  return var > 0 ? 0 : 1;
   // CHECK: {{.*}}XRay: Log file in '{{.*}}'
+  // CHECK-NOT: Failed
 }
 
 // We want to make sure that the order of the function log doesn't matter.