Abseil LTS 20200923

What's New:
* `absl::StatusOr<T>` has been released. See our [blog
  post](https://abseil.io/blog/2020-091021-status) for more
  information.
* Abseil Flags reflection interfaces have been released.
* Abseil Flags memory usage has been significantly optimized.
* Abseil now supports a "hardened" build mode. This build mode enables
  runtime checks that guard against programming errors that may lead
  to security vulnerabilities.

Notable Fixes:
* Sanitizer dynamic annotations like `AnnotateRWLockCreate` that are
  also defined by the compiler sanitizer implementation are no longer
  also defined by Abseil.
* Sanitizer macros are now prefixed with `ABSL_` to avoid naming collisions.
* Sanitizer usage is now automatically detected and no longer requires
  macros like `ADDRESS_SANITIZER` to be defined on the command line.

Breaking Changes:
* Abseil no longer contains a `dynamic_annotations` library. Users
  using a supported build system (Bazel or CMake) are unaffected by
  this, but users manually specifying link libraries may get an error
  about a missing linker input.

Baseline: 7680a5f8efe32de4753baadbd63e74e59d95bac1
Cherry picks: None

1 files changed, 28 insertions, 5 deletions

diff --git a/absl/base/internal/sysinfo.cc b/absl/base/internal/sysinfo.cc
index a0930e97..349d9268 100644
--- a/absl/base/internal/sysinfo.cc
+++ b/absl/base/internal/sysinfo.cc
@@ -39,6 +39,7 @@
 #endif
 
 #include <string.h>
+
 #include <cassert>
 #include <cstdint>
 #include <cstdio>
@@ -50,9 +51,11 @@
 #include <vector>
 
 #include "absl/base/call_once.h"
+#include "absl/base/config.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
@@ -72,6 +75,12 @@ static int GetNumCPUs() {
 #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
@@ -91,6 +100,7 @@ static double GetNominalCPUFrequency() {
     }
   }
   return 1.0;
+#endif  // WINAPI_PARTITION_APP && !WINAPI_PARTITION_DESKTOP
 }
 
 #elif defined(CTL_HW) && defined(HW_CPU_FREQ)
@@ -336,15 +346,16 @@ pid_t GetTID() {
 #else
 
 // Fallback implementation of GetTID using pthread_getspecific.
-static once_flag tid_once;
-static pthread_key_t tid_key;
-static absl::base_internal::SpinLock tid_lock(
-    absl::base_internal::kLinkerInitialized);
+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().
-static std::vector<uint32_t>* tid_array GUARDED_BY(tid_lock) = nullptr;
+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.
@@ -411,6 +422,18 @@ pid_t GetTID() {
 
 #endif
 
+// GetCachedTID() caches the thread ID in thread-local storage (which is a
+// userspace construct) to avoid unnecessary system calls. Without this caching,
+// it can take roughly 98ns, while it takes roughly 1ns with this caching.
+pid_t GetCachedTID() {
+#if ABSL_HAVE_THREAD_LOCAL
+  static thread_local pid_t thread_id = GetTID();
+  return thread_id;
+#else
+  return GetTID();
+#endif  // ABSL_HAVE_THREAD_LOCAL
+}
+
 }  // namespace base_internal
 ABSL_NAMESPACE_END
 }  // namespace absl