Rollback because of internal incompatibility.

PiperOrigin-RevId: 512979517
Change-Id: I7fe38ed246e42e6f8eb322e15c3b299215163168

3 files changed, 28 insertions, 151 deletions

diff --git a/absl/synchronization/internal/futex.h b/absl/synchronization/internal/futex.h
index 62bb40f7..9cf9841d 100644
--- a/absl/synchronization/internal/futex.h
+++ b/absl/synchronization/internal/futex.h
@@ -16,7 +16,9 @@
 
 #include "absl/base/config.h"
 
-#ifndef _WIN32
+#ifdef _WIN32
+#include <windows.h>
+#else
 #include <sys/time.h>
 #include <unistd.h>
 #endif
@@ -83,60 +85,34 @@ namespace synchronization_internal {
 
 class FutexImpl {
  public:
-  // Atomically check that `*v == val`, and if it is, then sleep until the
-  // timeout `t` has been reached, or until woken by `Wake()`.
-  static int WaitUntil(std::atomic<int32_t>* v, int32_t val,
+  static int WaitUntil(std::atomic<int32_t> *v, int32_t val,
                        KernelTimeout t) {
-    if (!t.has_timeout()) {
-      return Wait(v, val);
-    } else if (t.is_absolute_timeout()) {
-      auto abs_timespec = t.MakeAbsTimespec();
-      return WaitAbsoluteTimeout(v, val, &abs_timespec);
+    long err = 0;  // NOLINT(runtime/int)
+    if (t.has_timeout()) {
+      // https://locklessinc.com/articles/futex_cheat_sheet/
+      // Unlike FUTEX_WAIT, FUTEX_WAIT_BITSET uses absolute time.
+      struct timespec abs_timeout = t.MakeAbsTimespec();
+      // Atomically check that the futex value is still 0, and if it
+      // is, sleep until abs_timeout or until woken by FUTEX_WAKE.
+      err = syscall(
+          SYS_futex, reinterpret_cast<int32_t *>(v),
+          FUTEX_WAIT_BITSET | FUTEX_PRIVATE_FLAG | FUTEX_CLOCK_REALTIME, val,
+          &abs_timeout, nullptr, FUTEX_BITSET_MATCH_ANY);
     } else {
-      auto rel_timespec = t.MakeRelativeTimespec();
-      return WaitRelativeTimeout(v, val, &rel_timespec);
+      // Atomically check that the futex value is still 0, and if it
+      // is, sleep until woken by FUTEX_WAKE.
+      err = syscall(SYS_futex, reinterpret_cast<int32_t *>(v),
+                    FUTEX_WAIT | FUTEX_PRIVATE_FLAG, val, nullptr);
     }
-  }
-
-  // Atomically check that `*v == val`, and if it is, then sleep until the until
-  // woken by `Wake()`.
-  static int Wait(std::atomic<int32_t>* v, int32_t val) {
-    return WaitAbsoluteTimeout(v, val, nullptr);
-  }
-
-  // Atomically check that `*v == val`, and if it is, then sleep until
-  // CLOCK_REALTIME reaches `*abs_timeout`, or until woken by `Wake()`.
-  static int WaitAbsoluteTimeout(std::atomic<int32_t>* v, int32_t val,
-                                 const struct timespec* abs_timeout) {
-    // https://locklessinc.com/articles/futex_cheat_sheet/
-    // Unlike FUTEX_WAIT, FUTEX_WAIT_BITSET uses absolute time.
-    auto err =
-        syscall(SYS_futex, reinterpret_cast<int32_t*>(v),
-                FUTEX_WAIT_BITSET | FUTEX_PRIVATE_FLAG | FUTEX_CLOCK_REALTIME,
-                val, abs_timeout, nullptr, FUTEX_BITSET_MATCH_ANY);
-    if (err != 0) {
-      return -errno;
-    }
-    return 0;
-  }
-
-  // Atomically check that `*v == val`, and if it is, then sleep until
-  // `*rel_timeout` has elapsed, or until woken by `Wake()`.
-  static int WaitRelativeTimeout(std::atomic<int32_t>* v, int32_t val,
-                                 const struct timespec* rel_timeout) {
-    // Atomically check that the futex value is still 0, and if it
-    // is, sleep until abs_timeout or until woken by FUTEX_WAKE.
-    auto err = syscall(SYS_futex, reinterpret_cast<int32_t*>(v),
-                       FUTEX_PRIVATE_FLAG, val, rel_timeout);
-    if (err != 0) {
+    if (ABSL_PREDICT_FALSE(err != 0)) {
       return -errno;
     }
     return 0;
   }
 
-  // Wakes at most `count` waiters that have entered the sleep state on `v`.
-  static int Wake(std::atomic<int32_t>* v, int32_t count) {
-    auto err = syscall(SYS_futex, reinterpret_cast<int32_t*>(v),
+  static int Wake(std::atomic<int32_t> *v, int32_t count) {
+    // NOLINTNEXTLINE(runtime/int)
+    long err = syscall(SYS_futex, reinterpret_cast<int32_t*>(v),
                        FUTEX_WAKE | FUTEX_PRIVATE_FLAG, count);
     if (ABSL_PREDICT_FALSE(err < 0)) {
       return -errno;
diff --git a/absl/synchronization/internal/waiter.cc b/absl/synchronization/internal/waiter.cc
index 4eee1298..f2051d67 100644
--- a/absl/synchronization/internal/waiter.cc
+++ b/absl/synchronization/internal/waiter.cc
@@ -67,74 +67,11 @@ static void MaybeBecomeIdle() {
 
 #if ABSL_WAITER_MODE == ABSL_WAITER_MODE_FUTEX
 
-Waiter::Waiter() : futex_(0) {}
-
-bool Waiter::WaitAbsoluteTimeout(KernelTimeout t) {
-  // Loop until we can atomically decrement futex from a positive
-  // value, waiting on a futex while we believe it is zero.
-  // Note that, since the thread ticker is just reset, we don't need to check
-  // whether the thread is idle on the very first pass of the loop.
-  bool first_pass = true;
-
-  while (true) {
-    int32_t x = futex_.load(std::memory_order_relaxed);
-    while (x != 0) {
-      if (!futex_.compare_exchange_weak(x, x - 1,
-                                        std::memory_order_acquire,
-                                        std::memory_order_relaxed)) {
-        continue;  // Raced with someone, retry.
-      }
-      return true;  // Consumed a wakeup, we are done.
-    }
-
-    if (!first_pass) MaybeBecomeIdle();
-    auto abs_timeout = t.MakeAbsTimespec();
-    const int err = Futex::WaitAbsoluteTimeout(&futex_, 0, &abs_timeout);
-    if (err != 0) {
-      if (err == -EINTR || err == -EWOULDBLOCK) {
-        // Do nothing, the loop will retry.
-      } else if (err == -ETIMEDOUT) {
-        return false;
-      } else {
-        ABSL_RAW_LOG(FATAL, "Futex operation failed with error %d\n", err);
-      }
-    }
-    first_pass = false;
-  }
-}
-
-#ifdef CLOCK_MONOTONIC
-
-// Subtracts the timespec `sub` from `in` if the result would not be negative,
-// and returns true.  Returns false if the result would be negative, and leaves
-// `in` unchanged.
-static bool TimespecSubtract(struct timespec& in, const struct timespec& sub) {
-  if (in.tv_sec < sub.tv_sec) {
-    return false;
-  }
-  if (in.tv_nsec < sub.tv_nsec) {
-    if (in.tv_sec == sub.tv_sec) {
-      return false;
-    }
-    // Borrow from tv_sec.
-    in.tv_sec -= 1;
-    in.tv_nsec += 1'000'000'000;
-  }
-  in.tv_sec -= sub.tv_sec;
-  in.tv_nsec -= sub.tv_nsec;
-  return true;
+Waiter::Waiter() {
+  futex_.store(0, std::memory_order_relaxed);
 }
 
-// On some platforms a background thread periodically calls `Poke()` to briefly
-// wake waiter threads so that they may call `MaybeBecomeIdle()`. This means
-// that `WaitRelativeTimeout()` differs slightly from `WaitAbsoluteTimeout()`
-// because it must adjust the timeout by the amount of time that it has already
-// slept.
-bool Waiter::WaitRelativeTimeout(KernelTimeout t) {
-  struct timespec start;
-  ABSL_RAW_CHECK(clock_gettime(CLOCK_MONOTONIC, &start) == 0,
-                 "clock_gettime() failed");
-
+bool Waiter::Wait(KernelTimeout t) {
   // Loop until we can atomically decrement futex from a positive
   // value, waiting on a futex while we believe it is zero.
   // Note that, since the thread ticker is just reset, we don't need to check
@@ -152,24 +89,8 @@ bool Waiter::WaitRelativeTimeout(KernelTimeout t) {
       return true;  // Consumed a wakeup, we are done.
     }
 
-    auto relative_timeout = t.MakeRelativeTimespec();
-    if (!first_pass) {
-      MaybeBecomeIdle();
-
-      // Adjust relative_timeout for `Poke()`s.
-      struct timespec now;
-      ABSL_RAW_CHECK(clock_gettime(CLOCK_MONOTONIC, &now) == 0,
-                     "clock_gettime() failed");
-      // If TimespecSubstract(now, start) returns false, then the clock isn't
-      // truly monotonic.
-      if (TimespecSubtract(now, start)) {
-        if (!TimespecSubtract(relative_timeout, now)) {
-          return false;  // Timeout.
-        }
-      }
-    }
-
-    const int err = Futex::WaitRelativeTimeout(&futex_, 0, &relative_timeout);
+    if (!first_pass) MaybeBecomeIdle();
+    const int err = Futex::WaitUntil(&futex_, 0, t);
     if (err != 0) {
       if (err == -EINTR || err == -EWOULDBLOCK) {
         // Do nothing, the loop will retry.
@@ -183,23 +104,6 @@ bool Waiter::WaitRelativeTimeout(KernelTimeout t) {
   }
 }
 
-#else  // CLOCK_MONOTONIC
-
-// No support for CLOCK_MONOTONIC.
-// KernelTimeout will automatically convert to an absolute timeout.
-bool Waiter::WaitRelativeTimeout(KernelTimeout t) {
-  return WaitAbsoluteTimeout(t);
-}
-
-#endif  // CLOCK_MONOTONIC
-
-bool Waiter::Wait(KernelTimeout t) {
-  if (t.is_absolute_timeout()) {
-    return WaitAbsoluteTimeout(t);
-  }
-  return WaitRelativeTimeout(t);
-}
-
 void Waiter::Post() {
   if (futex_.fetch_add(1, std::memory_order_release) == 0) {
     // We incremented from 0, need to wake a potential waiter.
diff --git a/absl/synchronization/internal/waiter.h b/absl/synchronization/internal/waiter.h
index c206cc3f..b8adfeb5 100644
--- a/absl/synchronization/internal/waiter.h
+++ b/absl/synchronization/internal/waiter.h
@@ -110,9 +110,6 @@ class Waiter {
   ~Waiter() = delete;
 
 #if ABSL_WAITER_MODE == ABSL_WAITER_MODE_FUTEX
-  bool WaitAbsoluteTimeout(KernelTimeout t);
-  bool WaitRelativeTimeout(KernelTimeout t);
-
   // Futexes are defined by specification to be 32-bits.
   // Thus std::atomic<int32_t> must be just an int32_t with lockfree methods.
   std::atomic<int32_t> futex_;