Export of internal Abseil changes

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9fc37c11b9e46287acef00ee06ed9adcba54dd13 by Greg Falcon <gfalcon@google.com>:

Rename absl::hash_internal::HashState to absl::hash_internal::MixingHashState.

Before this change, we had two classes named HashState: absl::HashState, the public API used for type erasure, and absl::hash_internal::HashState, the internal concrete implementation ordinarily used.

The internal class used to be named `CityHashState`, but we renamed it to `HashState` it when we changed underlying hash implementation to wyhash.  This inadvertent naming conflict made the code much harder to read, and this change intends to undo that.

PiperOrigin-RevId: 373481959

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4aec55ffddebd085c239352a2e20721091f719a1 by Greg Falcon <gfalcon@google.com>:

Introduce absl::HashOf(), a convenience wrapper around absl::Hash that calculates hashes from the values of its arguments.

PiperOrigin-RevId: 373461406

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86b5fd8db50bbc8bd0aa9258523527381fe0445d by Abseil Team <absl-team@google.com>:

Improve speed of BlockingCounter by making its most common path lock free.

With the new implementation, the fast path of BlockingCounter::DecrementCount()
is only a fetch_sub operation. This is most times much more efficient than the
previous implementation (full mutex lock/unlock). As a matter of fact, in most
actual usecases in practice, the waiter thread is already waiting on the
Wait() call when DecrementCount() is called, which makes Mutex::Unlock() take
the slow path as there's a waiter thread that it might need to wake up.

PiperOrigin-RevId: 373394164

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65c876be5eac0cd32583ff8535ede4109d39cf3f by Martijn Vels <mvels@google.com>:

Move the 'sample copied cord' logic into MaybeTrackCord(),

This changes move the logic for selecting if a cord should remain being sampled from Cord to CordzInfo::MaybeTrackCord, and updates the documentation for the latter method.

PiperOrigin-RevId: 373363168

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e84410bd0aada293a81dfb82656c952e209e21fb by Martijn Vels <mvels@google.com>:

Add check for the first call to cordz_should_profile() for each thread.

This prevents the first cord of a newly created thread to be always sampled, which is a 'bad' kind of determinism for sampling.

PiperOrigin-RevId: 373229768

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bf09c589dc099ac8f4af780bf7e609c53c27574c by Samuel Benzaquen <sbenza@google.com>:

Refactor the Flags structure into an enum.
This gives us more control over the representation and allows for easier
merging during parsing.

PiperOrigin-RevId: 373163038

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b947b0c51083b7b6508284b5d31819596c91729e by Derek Mauro <dmauro@google.com>:

Fixes warnings about shadowed variables
Fixes #956

PiperOrigin-RevId: 373158133
GitOrigin-RevId: 9fc37c11b9e46287acef00ee06ed9adcba54dd13
Change-Id: I91f35699f9bf439d1a870c6493946a310afe088c

1 files changed, 2 insertions, 16 deletions

diff --git a/absl/strings/cord.cc b/absl/strings/cord.cc
index 5dad781e..f5aa6e47 100644
--- a/absl/strings/cord.cc
+++ b/absl/strings/cord.cc
@@ -536,24 +536,10 @@ void Cord::InlineRep::AssignSlow(const Cord::InlineRep& src) {
     return;
   }
 
-  // See b/187581164: unsample cord if already sampled
-  // TODO(b/117940323): continuously 'assigned to' cords would reach 100%
-  // sampling probability. Imagine a cord x in some cache:
-  //   cache.SetCord(const Cord& foo) {
-  //     x = foo;
-  //   }
-  // CordzInfo::MaybeTrackCord does:
-  // x.profiled = foo.profiled | x.profiled | random(cordz_mean_interval)
-  // Which means it will on the long run converge to 'always samples'
-  // The real fix is in CordzMaybeTrackCord, but the below is a low risk
-  // forward fix for b/187581164 and similar BT benchmark regressions.
-  if (ABSL_PREDICT_FALSE(is_profiled())) {
-    cordz_info()->Untrack();
-    clear_cordz_info();
-  }
-
   CordRep* tree = as_tree();
   if (CordRep* src_tree = src.tree()) {
+    // Leave any existing `cordz_info` in place, and let MaybeTrackCord()
+    // decide if this cord should be (or remains to be) sampled or not.
     data_.set_tree(CordRep::Ref(src_tree));
     CordzInfo::MaybeTrackCord(data_, src.data_, method);
   } else {