Add 'third_party/abseil_cpp/' from commit '768eb2ca2857342673fcd462792ce04b8bac3fa3' r/781

git-subtree-dir: third_party/abseil_cpp
git-subtree-mainline: ffb2ae54beb5796cd408fbe15d2d2da09ff37adf
git-subtree-split: 768eb2ca2857342673fcd462792ce04b8bac3fa3

1 files changed, 425 insertions, 0 deletions

diff --git a/third_party/abseil_cpp/absl/base/internal/sysinfo.cc b/third_party/abseil_cpp/absl/base/internal/sysinfo.cc
new file mode 100644
index 000000000000..6c69683faf67
--- /dev/null
+++ b/third_party/abseil_cpp/absl/base/internal/sysinfo.cc
@@ -0,0 +1,425 @@
+// Copyright 2017 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+#include "absl/base/internal/sysinfo.h"
+
+#include "absl/base/attributes.h"
+
+#ifdef _WIN32
+#include <windows.h>
+#else
+#include <fcntl.h>
+#include <pthread.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+#endif
+
+#ifdef __linux__
+#include <sys/syscall.h>
+#endif
+
+#if defined(__APPLE__) || defined(__FreeBSD__)
+#include <sys/sysctl.h>
+#endif
+
+#if defined(__myriad2__)
+#include <rtems.h>
+#endif
+
+#include <string.h>
+#include <cassert>
+#include <cstdint>
+#include <cstdio>
+#include <cstdlib>
+#include <ctime>
+#include <limits>
+#include <thread>  // NOLINT(build/c++11)
+#include <utility>
+#include <vector>
+
+#include "absl/base/call_once.h"
+#include "absl/base/internal/raw_logging.h"
+#include "absl/base/internal/spinlock.h"
+#include "absl/base/internal/unscaledcycleclock.h"
+#include "absl/base/thread_annotations.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace base_internal {
+
+static int GetNumCPUs() {
+#if defined(__myriad2__)
+  return 1;
+#else
+  // Other possibilities:
+  //  - Read /sys/devices/system/cpu/online and use cpumask_parse()
+  //  - sysconf(_SC_NPROCESSORS_ONLN)
+  return std::thread::hardware_concurrency();
+#endif
+}
+
+#if defined(_WIN32)
+
+static double GetNominalCPUFrequency() {
+#if WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_APP) && \
+    !WINAPI_FAMILY_PARTITION(WINAPI_PARTITION_DESKTOP)
+  // UWP apps don't have access to the registry and currently don't provide an
+  // API informing about CPU nominal frequency.
+  return 1.0;
+#else
+#pragma comment(lib, "advapi32.lib")  // For Reg* functions.
+  HKEY key;
+  // Use the Reg* functions rather than the SH functions because shlwapi.dll
+  // pulls in gdi32.dll which makes process destruction much more costly.
+  if (RegOpenKeyExA(HKEY_LOCAL_MACHINE,
+                    "HARDWARE\\DESCRIPTION\\System\\CentralProcessor\\0", 0,
+                    KEY_READ, &key) == ERROR_SUCCESS) {
+    DWORD type = 0;
+    DWORD data = 0;
+    DWORD data_size = sizeof(data);
+    auto result = RegQueryValueExA(key, "~MHz", 0, &type,
+                                   reinterpret_cast<LPBYTE>(&data), &data_size);
+    RegCloseKey(key);
+    if (result == ERROR_SUCCESS && type == REG_DWORD &&
+        data_size == sizeof(data)) {
+      return data * 1e6;  // Value is MHz.
+    }
+  }
+  return 1.0;
+#endif  // WINAPI_PARTITION_APP && !WINAPI_PARTITION_DESKTOP
+}
+
+#elif defined(CTL_HW) && defined(HW_CPU_FREQ)
+
+static double GetNominalCPUFrequency() {
+  unsigned freq;
+  size_t size = sizeof(freq);
+  int mib[2] = {CTL_HW, HW_CPU_FREQ};
+  if (sysctl(mib, 2, &freq, &size, nullptr, 0) == 0) {
+    return static_cast<double>(freq);
+  }
+  return 1.0;
+}
+
+#else
+
+// Helper function for reading a long from a file. Returns true if successful
+// and the memory location pointed to by value is set to the value read.
+static bool ReadLongFromFile(const char *file, long *value) {
+  bool ret = false;
+  int fd = open(file, O_RDONLY);
+  if (fd != -1) {
+    char line[1024];
+    char *err;
+    memset(line, '\0', sizeof(line));
+    int len = read(fd, line, sizeof(line) - 1);
+    if (len <= 0) {
+      ret = false;
+    } else {
+      const long temp_value = strtol(line, &err, 10);
+      if (line[0] != '\0' && (*err == '\n' || *err == '\0')) {
+        *value = temp_value;
+        ret = true;
+      }
+    }
+    close(fd);
+  }
+  return ret;
+}
+
+#if defined(ABSL_INTERNAL_UNSCALED_CYCLECLOCK_FREQUENCY_IS_CPU_FREQUENCY)
+
+// Reads a monotonic time source and returns a value in
+// nanoseconds. The returned value uses an arbitrary epoch, not the
+// Unix epoch.
+static int64_t ReadMonotonicClockNanos() {
+  struct timespec t;
+#ifdef CLOCK_MONOTONIC_RAW
+  int rc = clock_gettime(CLOCK_MONOTONIC_RAW, &t);
+#else
+  int rc = clock_gettime(CLOCK_MONOTONIC, &t);
+#endif
+  if (rc != 0) {
+    perror("clock_gettime() failed");
+    abort();
+  }
+  return int64_t{t.tv_sec} * 1000000000 + t.tv_nsec;
+}
+
+class UnscaledCycleClockWrapperForInitializeFrequency {
+ public:
+  static int64_t Now() { return base_internal::UnscaledCycleClock::Now(); }
+};
+
+struct TimeTscPair {
+  int64_t time;  // From ReadMonotonicClockNanos().
+  int64_t tsc;   // From UnscaledCycleClock::Now().
+};
+
+// Returns a pair of values (monotonic kernel time, TSC ticks) that
+// approximately correspond to each other.  This is accomplished by
+// doing several reads and picking the reading with the lowest
+// latency.  This approach is used to minimize the probability that
+// our thread was preempted between clock reads.
+static TimeTscPair GetTimeTscPair() {
+  int64_t best_latency = std::numeric_limits<int64_t>::max();
+  TimeTscPair best;
+  for (int i = 0; i < 10; ++i) {
+    int64_t t0 = ReadMonotonicClockNanos();
+    int64_t tsc = UnscaledCycleClockWrapperForInitializeFrequency::Now();
+    int64_t t1 = ReadMonotonicClockNanos();
+    int64_t latency = t1 - t0;
+    if (latency < best_latency) {
+      best_latency = latency;
+      best.time = t0;
+      best.tsc = tsc;
+    }
+  }
+  return best;
+}
+
+// Measures and returns the TSC frequency by taking a pair of
+// measurements approximately `sleep_nanoseconds` apart.
+static double MeasureTscFrequencyWithSleep(int sleep_nanoseconds) {
+  auto t0 = GetTimeTscPair();
+  struct timespec ts;
+  ts.tv_sec = 0;
+  ts.tv_nsec = sleep_nanoseconds;
+  while (nanosleep(&ts, &ts) != 0 && errno == EINTR) {}
+  auto t1 = GetTimeTscPair();
+  double elapsed_ticks = t1.tsc - t0.tsc;
+  double elapsed_time = (t1.time - t0.time) * 1e-9;
+  return elapsed_ticks / elapsed_time;
+}
+
+// Measures and returns the TSC frequency by calling
+// MeasureTscFrequencyWithSleep(), doubling the sleep interval until the
+// frequency measurement stabilizes.
+static double MeasureTscFrequency() {
+  double last_measurement = -1.0;
+  int sleep_nanoseconds = 1000000;  // 1 millisecond.
+  for (int i = 0; i < 8; ++i) {
+    double measurement = MeasureTscFrequencyWithSleep(sleep_nanoseconds);
+    if (measurement * 0.99 < last_measurement &&
+        last_measurement < measurement * 1.01) {
+      // Use the current measurement if it is within 1% of the
+      // previous measurement.
+      return measurement;
+    }
+    last_measurement = measurement;
+    sleep_nanoseconds *= 2;
+  }
+  return last_measurement;
+}
+
+#endif  // ABSL_INTERNAL_UNSCALED_CYCLECLOCK_FREQUENCY_IS_CPU_FREQUENCY
+
+static double GetNominalCPUFrequency() {
+  long freq = 0;
+
+  // Google's production kernel has a patch to export the TSC
+  // frequency through sysfs. If the kernel is exporting the TSC
+  // frequency use that. There are issues where cpuinfo_max_freq
+  // cannot be relied on because the BIOS may be exporting an invalid
+  // p-state (on x86) or p-states may be used to put the processor in
+  // a new mode (turbo mode). Essentially, those frequencies cannot
+  // always be relied upon. The same reasons apply to /proc/cpuinfo as
+  // well.
+  if (ReadLongFromFile("/sys/devices/system/cpu/cpu0/tsc_freq_khz", &freq)) {
+    return freq * 1e3;  // Value is kHz.
+  }
+
+#if defined(ABSL_INTERNAL_UNSCALED_CYCLECLOCK_FREQUENCY_IS_CPU_FREQUENCY)
+  // On these platforms, the TSC frequency is the nominal CPU
+  // frequency.  But without having the kernel export it directly
+  // though /sys/devices/system/cpu/cpu0/tsc_freq_khz, there is no
+  // other way to reliably get the TSC frequency, so we have to
+  // measure it ourselves.  Some CPUs abuse cpuinfo_max_freq by
+  // exporting "fake" frequencies for implementing new features. For
+  // example, Intel's turbo mode is enabled by exposing a p-state
+  // value with a higher frequency than that of the real TSC
+  // rate. Because of this, we prefer to measure the TSC rate
+  // ourselves on i386 and x86-64.
+  return MeasureTscFrequency();
+#else
+
+  // If CPU scaling is in effect, we want to use the *maximum*
+  // frequency, not whatever CPU speed some random processor happens
+  // to be using now.
+  if (ReadLongFromFile("/sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_max_freq",
+                       &freq)) {
+    return freq * 1e3;  // Value is kHz.
+  }
+
+  return 1.0;
+#endif  // !ABSL_INTERNAL_UNSCALED_CYCLECLOCK_FREQUENCY_IS_CPU_FREQUENCY
+}
+
+#endif
+
+ABSL_CONST_INIT static once_flag init_num_cpus_once;
+ABSL_CONST_INIT static int num_cpus = 0;
+
+// NumCPUs() may be called before main() and before malloc is properly
+// initialized, therefore this must not allocate memory.
+int NumCPUs() {
+  base_internal::LowLevelCallOnce(
+      &init_num_cpus_once, []() { num_cpus = GetNumCPUs(); });
+  return num_cpus;
+}
+
+// A default frequency of 0.0 might be dangerous if it is used in division.
+ABSL_CONST_INIT static once_flag init_nominal_cpu_frequency_once;
+ABSL_CONST_INIT static double nominal_cpu_frequency = 1.0;
+
+// NominalCPUFrequency() may be called before main() and before malloc is
+// properly initialized, therefore this must not allocate memory.
+double NominalCPUFrequency() {
+  base_internal::LowLevelCallOnce(
+      &init_nominal_cpu_frequency_once,
+      []() { nominal_cpu_frequency = GetNominalCPUFrequency(); });
+  return nominal_cpu_frequency;
+}
+
+#if defined(_WIN32)
+
+pid_t GetTID() {
+  return pid_t{GetCurrentThreadId()};
+}
+
+#elif defined(__linux__)
+
+#ifndef SYS_gettid
+#define SYS_gettid __NR_gettid
+#endif
+
+pid_t GetTID() {
+  return syscall(SYS_gettid);
+}
+
+#elif defined(__akaros__)
+
+pid_t GetTID() {
+  // Akaros has a concept of "vcore context", which is the state the program
+  // is forced into when we need to make a user-level scheduling decision, or
+  // run a signal handler.  This is analogous to the interrupt context that a
+  // CPU might enter if it encounters some kind of exception.
+  //
+  // There is no current thread context in vcore context, but we need to give
+  // a reasonable answer if asked for a thread ID (e.g., in a signal handler).
+  // Thread 0 always exists, so if we are in vcore context, we return that.
+  //
+  // Otherwise, we know (since we are using pthreads) that the uthread struct
+  // current_uthread is pointing to is the first element of a
+  // struct pthread_tcb, so we extract and return the thread ID from that.
+  //
+  // TODO(dcross): Akaros anticipates moving the thread ID to the uthread
+  // structure at some point. We should modify this code to remove the cast
+  // when that happens.
+  if (in_vcore_context())
+    return 0;
+  return reinterpret_cast<struct pthread_tcb *>(current_uthread)->id;
+}
+
+#elif defined(__myriad2__)
+
+pid_t GetTID() {
+  uint32_t tid;
+  rtems_task_ident(RTEMS_SELF, 0, &tid);
+  return tid;
+}
+
+#else
+
+// Fallback implementation of GetTID using pthread_getspecific.
+ABSL_CONST_INIT static once_flag tid_once;
+ABSL_CONST_INIT static pthread_key_t tid_key;
+ABSL_CONST_INIT static absl::base_internal::SpinLock tid_lock(
+    absl::kConstInit, base_internal::SCHEDULE_KERNEL_ONLY);
+
+// We set a bit per thread in this array to indicate that an ID is in
+// use. ID 0 is unused because it is the default value returned by
+// pthread_getspecific().
+ABSL_CONST_INIT static std::vector<uint32_t> *tid_array
+    ABSL_GUARDED_BY(tid_lock) = nullptr;
+static constexpr int kBitsPerWord = 32;  // tid_array is uint32_t.
+
+// Returns the TID to tid_array.
+static void FreeTID(void *v) {
+  intptr_t tid = reinterpret_cast<intptr_t>(v);
+  int word = tid / kBitsPerWord;
+  uint32_t mask = ~(1u << (tid % kBitsPerWord));
+  absl::base_internal::SpinLockHolder lock(&tid_lock);
+  assert(0 <= word && static_cast<size_t>(word) < tid_array->size());
+  (*tid_array)[word] &= mask;
+}
+
+static void InitGetTID() {
+  if (pthread_key_create(&tid_key, FreeTID) != 0) {
+    // The logging system calls GetTID() so it can't be used here.
+    perror("pthread_key_create failed");
+    abort();
+  }
+
+  // Initialize tid_array.
+  absl::base_internal::SpinLockHolder lock(&tid_lock);
+  tid_array = new std::vector<uint32_t>(1);
+  (*tid_array)[0] = 1;  // ID 0 is never-allocated.
+}
+
+// Return a per-thread small integer ID from pthread's thread-specific data.
+pid_t GetTID() {
+  absl::call_once(tid_once, InitGetTID);
+
+  intptr_t tid = reinterpret_cast<intptr_t>(pthread_getspecific(tid_key));
+  if (tid != 0) {
+    return tid;
+  }
+
+  int bit;  // tid_array[word] = 1u << bit;
+  size_t word;
+  {
+    // Search for the first unused ID.
+    absl::base_internal::SpinLockHolder lock(&tid_lock);
+    // First search for a word in the array that is not all ones.
+    word = 0;
+    while (word < tid_array->size() && ~(*tid_array)[word] == 0) {
+      ++word;
+    }
+    if (word == tid_array->size()) {
+      tid_array->push_back(0);  // No space left, add kBitsPerWord more IDs.
+    }
+    // Search for a zero bit in the word.
+    bit = 0;
+    while (bit < kBitsPerWord && (((*tid_array)[word] >> bit) & 1) != 0) {
+      ++bit;
+    }
+    tid = (word * kBitsPerWord) + bit;
+    (*tid_array)[word] |= 1u << bit;  // Mark the TID as allocated.
+  }
+
+  if (pthread_setspecific(tid_key, reinterpret_cast<void *>(tid)) != 0) {
+    perror("pthread_setspecific failed");
+    abort();
+  }
+
+  return static_cast<pid_t>(tid);
+}
+
+#endif
+
+}  // namespace base_internal
+ABSL_NAMESPACE_END
+}  // namespace absl