Add MakeAbsNs to KernelTimeout.

Rather than add new friends every time
a new (internal) use arises, just expose
the timestamp.

PiperOrigin-RevId: 495722262
Change-Id: I25d2ce64769dc58cbe634259f07c600ce6c1e714

absl/synchronization/internal/kernel_timeout.h

@@ -28,6 +28,7 @@
 #include <time.h>
 
 #include <algorithm>
+#include <cstdint>
 #include <limits>
 
 #include "absl/base/internal/raw_logging.h"
@@ -60,7 +61,10 @@ class KernelTimeout {
 
   // Convert to parameter for sem_timedwait/futex/similar.  Only for approved
   // users.  Do not call if !has_timeout.
-  struct timespec MakeAbsTimespec();
+  struct timespec MakeAbsTimespec() const;
+
+  // Convert to unix epoch nanos.  Do not call if !has_timeout.
+  int64_t MakeAbsNanos() const;
 
  private:
   // internal rep, not user visible: ns after unix epoch.
@@ -126,7 +130,7 @@ class KernelTimeout {
   friend class Waiter;
 };
 
-inline struct timespec KernelTimeout::MakeAbsTimespec() {
+inline struct timespec KernelTimeout::MakeAbsTimespec() const {
   int64_t n = ns_;
   static const int64_t kNanosPerSecond = 1000 * 1000 * 1000;
   if (n == 0) {
@@ -150,6 +154,17 @@ inline struct timespec KernelTimeout::MakeAbsTimespec() {
   return abstime;
 }
 
+inline int64_t KernelTimeout::MakeAbsNanos() const {
+  if (ns_ == 0) {
+    ABSL_RAW_LOG(
+        ERROR, "Tried to create a timeout from a non-timeout; never do this.");
+    // But we'll try to continue sanely.  no-timeout ~= saturated timeout.
+    return (std::numeric_limits<int64_t>::max)();
+  }
+
+  return ns_;
+}
+
 }  // namespace synchronization_internal
 ABSL_NAMESPACE_END
 }  // namespace absl