Export of internal Abseil changes

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873b52b0a691e759413c5db27dafc541a5da5263 by Andy Getzendanner <durandal@google.com>:

Introduce an internal-only thread-local caching wrapper around GetTID.

PiperOrigin-RevId: 323055682

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091a4537f1ef6e158acbf4261cfae1af7a3bdb7f by Abseil Team <absl-team@google.com>:

Internal change

PiperOrigin-RevId: 322864497

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c80ccfff2a825819f31826a30f48cca3297699f8 by Evan Brown <ezb@google.com>:

Roll forward b-tree changes simplifying deletion and getting rid of recursion in clear_and_delete().

We also change clear_and_delete() to avoid some unnecessary comparisons by restructuring the loops.

PiperOrigin-RevId: 322658938

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81464c0fb9c8c6268dca2e530aba99e75e1e59ae by Gennadiy Rozental <rogeeff@google.com>:

Eliminate definition of RunningOnValgrind inside the library.

Fixes #674
Fixes #657

PiperOrigin-RevId: 322508440
GitOrigin-RevId: 873b52b0a691e759413c5db27dafc541a5da5263
Change-Id: I20b40c9e8fc62edcf981caab467cca33cf6fd2ba

2 files changed, 22 insertions, 0 deletions

diff --git a/absl/base/internal/sysinfo.cc b/absl/base/internal/sysinfo.cc
index 6c69683f..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>
@@ -50,6 +51,7 @@
 #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"
@@ -420,6 +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
diff --git a/absl/base/internal/sysinfo.h b/absl/base/internal/sysinfo.h
index 7246d5dd..119cf1f0 100644
--- a/absl/base/internal/sysinfo.h
+++ b/absl/base/internal/sysinfo.h
@@ -30,6 +30,7 @@
 
 #include <cstdint>
 
+#include "absl/base/config.h"
 #include "absl/base/port.h"
 
 namespace absl {
@@ -59,6 +60,13 @@ using pid_t = uint32_t;
 #endif
 pid_t GetTID();
 
+// Like GetTID(), but caches the result in thread-local storage in order
+// to avoid unnecessary system calls. Note that there are some cases where
+// one must call through to GetTID directly, which is why this exists as a
+// separate function. For example, GetCachedTID() is not safe to call in
+// an asynchronous signal-handling context nor right after a call to fork().
+pid_t GetCachedTID();
+
 }  // namespace base_internal
 ABSL_NAMESPACE_END
 }  // namespace absl