[libc-commits] [libc] [libc] implement cached process/thread identity (PR #95965)

[Nick Desaulniers via libc-commits]

================
@@ -0,0 +1,43 @@
+//===------------ pid_t utilities -------------------------------*- C++ -*-===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_LIBC_SRC___SUPPORT_OSUTIL_PID_H
+#define LLVM_LIBC_SRC___SUPPORT_OSUTIL_PID_H
+#include "hdr/types/pid_t.h"
+#include "src/__support/macros/attributes.h"
+#include "src/__support/macros/optimization.h"
+
+#ifndef LIBC_COPT_ENABLE_PID_CACHE
+#define LIBC_COPT_ENABLE_PID_CACHE 1
+#endif
+
+namespace LIBC_NAMESPACE {
+
+class ProcessIdentity {
+  static thread_local bool fork_inflight;
+  static pid_t cache;
+  static pid_t get_uncached();
+
+public:
+  LIBC_INLINE static void start_fork() { fork_inflight = true; }
+  LIBC_INLINE static void end_fork() { fork_inflight = false; }
+  LIBC_INLINE static void refresh_cache() { cache = get_uncached(); }
+  LIBC_INLINE static pid_t get() {
+#if LIBC_COPT_ENABLE_PID_CACHE
+    if (LIBC_UNLIKELY(fork_inflight))
+      return get_uncached();
+    return cache;
+#else
+    return get_uncached();
+#endif
----------------
nickdesaulniers wrote:

```suggestion
#if LIBC_COPT_ENABLE_PID_CACHE
    if (LIBC_LIKELY(!fork_inflight))
      return cache;
#endif
    return get_uncached();
```

https://github.com/llvm/llvm-project/pull/95965