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, 8 insertions, 2 deletions

diff --git a/absl/strings/internal/cordz_functions.cc b/absl/strings/internal/cordz_functions.cc
index 6ad864f1..f30080f8 100644
--- a/absl/strings/internal/cordz_functions.cc
+++ b/absl/strings/internal/cordz_functions.cc
@@ -44,7 +44,10 @@ std::atomic<int> g_cordz_mean_interval(50000);
 
 #ifdef ABSL_INTERNAL_CORDZ_ENABLED
 
-ABSL_CONST_INIT thread_local int64_t cordz_next_sample = 0;
+// Special negative 'not initialized' per thread value for cordz_next_sample.
+static constexpr int64_t kInitCordzNextSample = -1;
+
+ABSL_CONST_INIT thread_local int64_t cordz_next_sample = kInitCordzNextSample;
 
 // kIntervalIfDisabled is the number of profile-eligible events need to occur
 // before the code will confirm that cordz is still disabled.
@@ -77,8 +80,11 @@ ABSL_ATTRIBUTE_NOINLINE bool cordz_should_profile_slow() {
   }
 
   if (cordz_next_sample <= 0) {
+    // If first check on current thread, check cordz_should_profile()
+    // again using the created (initial) stride in cordz_next_sample.
+    const bool initialized = cordz_next_sample != kInitCordzNextSample;
     cordz_next_sample = exponential_biased_generator.GetStride(mean_interval);
-    return true;
+    return initialized || cordz_should_profile();
   }
 
   --cordz_next_sample;