Both Mutex and CondVar signal PerThreadSem/Waiter after satisfying the wait condition,
as the result the waiting thread may return w/o waiting on the
PerThreadSem/Waiter at all. If the waiting thread then exits, it currently
destroys Waiter object. As the result Waiter::Post can be called on
already destroyed object.
PerThreadSem/Waiter must be type-stable after creation and must not be destroyed.
The futex-based implementation is the only one that is not affected by the bug
since there is effectively nothing to destroy (maybe only UBSan/ASan
could complain about calling methods on a destroyed object).

Here is the problematic sequence of events:

1: void Mutex::Block(PerThreadSynch *s) {
2:   while (s->state.load(std::memory_order_acquire) == PerThreadSynch::kQueued) {
3:     if (!DecrementSynchSem(this, s, s->waitp->timeout)) {

4: PerThreadSynch *Mutex::Wakeup(PerThreadSynch *w) {
5:   ...
6:   w->state.store(PerThreadSynch::kAvailable, std::memory_order_release);
7:   IncrementSynchSem(this, w);
8:   ...
9: }

Consider line 6 is executed, then line 2 observes kAvailable and
line 3 is not called. The thread executing Mutex::Block returns from
the method, acquires the mutex, releases the mutex, exits and destroys
PerThreadSem/Waiter.
Now Mutex::Wakeup resumes and executes line 7 on the destroyed object. Boom!

CondVar uses a similar pattern.

Moreover the semaphore-based Waiter implementation is not even destruction-safe
(the Waiter cannot be used to signal own destruction). So even if Mutex/CondVar
would always pair Waiter::Post with Waiter::Wait before destroying PerThreadSem/Waiter,
it would still be subject to use-after-free bug on the semaphore.

PiperOrigin-RevId: 449159939
Change-Id: I497134fa8b6ce1294a422827c5f0de0e897cea31

CondVar::WaitWithTimeout can live-lock when timeout is racing with Signal/SignalAll
and Signal/SignalAll thread is not scheduled due to priorities, affinity or other
scheduler artifacts. This could lead to stalls of up to tens of seconds in some cases.
PiperOrigin-RevId: 449159670
Change-Id: I64bbd277c1f91964cfba3306ba8a80eeadf85f64

PiperOrigin-RevId: 449067700
Change-Id: I972b1736c28d76ed500e9ad6fd15c7a469a5825f

PiperOrigin-RevId: 448582508
Change-Id: I67fbff5f42a083e093ea2c20749e073ca03feb0b

PiperOrigin-RevId: 448361090
Change-Id: Iec6063b88a778dfe815081612650eaa456503265

Stop the absl::Cord destructor from running on the constinit cord in
CordTest.ConstinitConstructor. This allows inspecting the cord at any point
while the test is exiting, which is important for the semantics of the test.

PiperOrigin-RevId: 448327386
Change-Id: Icef9faa2b63f1f0ae60b3430dcf6184f5dead885

PiperOrigin-RevId: 448159349
Change-Id: I6b25a90d8a3b6d3a888274d156aa696d77fb042d

PiperOrigin-RevId: 448075898
Change-Id: Ia4047f833bf27c62752b41f4ba65ab3be88a0181

* Avoid warnings due to deprecation of volatile return types.

Also fix up optional_test.cc due to ABSL_USES_STD_OPTIONAL always being
false in its body.

Bug: chromium:1284275
PiperOrigin-RevId: 447796238
Change-Id: If050206c979c6c08af22e71ff0ea91e7f7932f0c

PiperOrigin-RevId: 446725910
Change-Id: I291fa8c1c41155b1530969f64b2b7f44b1576c92

raw_logging: Rename SafeWriteToStderr to indicate what about it is safe (answer: it's async-signal-safe).

Also, preserve errno across calls to make it actually signal-safe.

PiperOrigin-RevId: 446620926
Change-Id: I875fbec02b909e8424ddf763303b0d6007f8548f

Also note that this probe sequence visits every group exactly once.

PiperOrigin-RevId: 446535602
Change-Id: I13169be3f8ee6a4ddbbe8be84f1e1a482444d0cc

Improve analysis of the number of extra `==` operations, which was overly complicated, slightly incorrect.

The old analysis viewed it as birthday attack, which asks how often
there are multiple values in the probe same probe sequence with the
same H2.  In their own words, this analysis "breaks down" at around `n
= 12`.

Instead we can answer a simpler question, which is, if a probe
sequence examines `k` objects that are not what we are looking for,
what's the number of calls `==`?  The expectation is simply `k/128`.

PiperOrigin-RevId: 446518063
Change-Id: Ie879bd4f6c97979822bc9d550b9e2503b1418c78

We also add accessors for rightmost()/mutable_rightmost().

PiperOrigin-RevId: 446515231
Change-Id: I4b8cb46f4bd209a0f51dcdcb96c9479e480828a3

PiperOrigin-RevId: 446476285
Change-Id: Ibd0913e06244424241200d17177a4f220fcb7861

PiperOrigin-RevId: 446274314
Change-Id: Ibf641808c533a10e0aef8d1601095e539ae5c43a

PiperOrigin-RevId: 446209567
Change-Id: I9aac8ce10b93ed71f1260931995af1d32db6f780

PiperOrigin-RevId: 446010475
Change-Id: I28020510f3888a11f35b1960e9af441145ebf39b

PiperOrigin-RevId: 445394311
Change-Id: I265b6a83f79bbed4321e24e6da4730a2c43ddb07

Fixes #1159

PiperOrigin-RevId: 444278141
Change-Id: Iae055fe78b438c31150a9e7601b734f4981f002e

PiperOrigin-RevId: 444259007
Change-Id: Ic518f66a33e387b7a551f37f7c0f6003c743dcb0

PiperOrigin-RevId: 443726104
Change-Id: Ibd015472fe3e403c2da49bdeeb365ca9a817b8a5

PiperOrigin-RevId: 443723710
Change-Id: Ic39b0cf2b289efa9cd9434616949dd08a1a35117

--
6d4e969ad240d248bfeb644b3b76fffae0f07882 by Christian Blichmann <cblichmann@google.com>:

cmake: Fix description of `ABSL_USE_EXTERNAL_GOOGLETEST` option

There is no `add_subproject()` in CMake.

PiperOrigin-RevId: 443087953
Change-Id: I30c2118638f99ad1389ae197e2c81d1e5f298882
GitOrigin-RevId: 6d4e969ad240d248bfeb644b3b76fffae0f07882

--
6457ad659de86ce4cae1e9f7cb03a701c6c2851e by Abseil Team <absl-team@google.com>:

Introduced ErrnoToStatusCode and ErrnoToStatus to abseil.

PiperOrigin-RevId: 442903450
Change-Id: I9c062b34a3811216f43eef56e631eada3b4e3e84
GitOrigin-RevId: 6457ad659de86ce4cae1e9f7cb03a701c6c2851e

--
3d018c03a34bf273a4b24b3584ed77f0a6d21686 by Abseil Team <absl-team@google.com>:

Fix a spelling typo (s/boundries/boundaries).

PiperOrigin-RevId: 442041877
Change-Id: I608020697d37b85316bb9a0838e4b457659c926c

--
518b8119e51db24ce7fb0fd2fe537ec43825c3e6 by Dino Radakovic <dinor@google.com>:

absl/types/internal/variant: Make include guard uppercase

https://google.github.io/styleguide/cppguide.html#The__define_Guard

PiperOrigin-RevId: 441911692
Change-Id: I9837dd07f20204d8253f20627b0917a34dc21825

--
b91696c38310a7cae8c1ea9e2d479495f5dc3f69 by Greg Falcon <gfalcon@google.com>:

Add an internal-only API to wrap __builtin_prefetch() if available.

This private API is intended for future use by the Abseil implementation.  Like any internal-namespaced function, it may be changed or removed at any time.

PiperOrigin-RevId: 441894616
Change-Id: Iaa48bd4680b373f4a0d5afab0cb35e2a1908595f

--
0f01e8b0551a662e02dff60840c54320f987315f by Derek Mauro <dmauro@google.com>:

C++20: Use the standard `constinit` keyword for `ABSL_CONST_INIT` when available

PiperOrigin-RevId: 441778874
Change-Id: I70c616469752ff23b326b1c615437599f42cc6aa
GitOrigin-RevId: 3d018c03a34bf273a4b24b3584ed77f0a6d21686

--
155545fafefd0a0cef83853f1addea1ecf4a4618 by Derek Mauro <dmauro@google.com>:

Support ABSL_ATTRIBUTE_NO_SANITIZE_ADDRESS on MSVC

https://docs.microsoft.com/en-us/cpp/cpp/no-sanitize-address

PiperOrigin-RevId: 441737758
Change-Id: Ida9b185a929ffa22ad2ffdcfbd53076f69bfc036
GitOrigin-RevId: 155545fafefd0a0cef83853f1addea1ecf4a4618

--
f4c7e510922668c68be4aa79a00867c3d3ca9f95 by Derek Mauro <dmauro@google.com>:

Many improvements to LeakChecker builds

The presence of the LeakChecker is now detected when possible. GCC
users using LeakChecker in standalone mode still need to use
-DLEAK_CHECKER. This is now documented in the header.

The hacky targets used for testing leak checking have been removed in
favor of testing in AddressSanitizer mode on Kokoro.

Fixes #885
Fixes #1153

PiperOrigin-RevId: 441203393
Change-Id: Ibe64ef6b104bcaf31839ff7184e558cc86abdd1c

--
5c70a23aa83b8152ab95d2cf21662fc63c80ef7d by Abseil Team <absl-team@google.com>:

Add a benchmark for stacktrace

PiperOrigin-RevId: 441196473
Change-Id: I4c9aa2e797aa2cae09abfaaee3abe5c09eb62fc4

--
50b406052273b9d5bad04a7860a96e4d5d956c02 by Abseil Team <absl-team@google.com>:

Internal change.

PiperOrigin-RevId: 441114481
Change-Id: I667af7a50d5631ca91289dd24c91ba90233e0184

--
568b4eaac120b420bce5290179d407d2b57d5bae by Dino Radakovic <dinor@google.com>:

Internal change

PiperOrigin-RevId: 440894155
Change-Id: Ia587ffc65a8321126585fb363b7c0ca8cc2a0da2

--
d53948eace4f3a10ac5a6c1496dc51b81adc412c by Abseil Team <absl-team@google.com>:

Explicitly give internal linkage to symbols which are not used outside of their
translation units.

PiperOrigin-RevId: 440424519
Change-Id: I531c5e229d443375483b7550a34f48042589a99b
GitOrigin-RevId: f4c7e510922668c68be4aa79a00867c3d3ca9f95

--
0c8848ebedc07470c7ab647a5bb8949481540ce9 by Dino Radakovic <dinor@google.com>:

Define absl::base_internal::invoke using std::invoke when C++ >= 17

PiperOrigin-RevId: 439880834
Change-Id: I3622fcf473501d54c57575118a11d54c19573446
GitOrigin-RevId: 0c8848ebedc07470c7ab647a5bb8949481540ce9

--
ef2bf829c333f378ecc12f3259e3187cdb75a3d5 by Abseil Team <absl-team@google.com>:

debugging: fix the VDSO symbol name used for unwinding on RISC-V Linux

The name listed in `man vdso` is incorrect. Instead, use the name from `linux-5.16/arch/riscv/kernel/vdso/rt_sigreturn.S`

PiperOrigin-RevId: 439654174
Change-Id: Ib39d066f416681720068e806e828a2c76a14a532

--
43dfad824afd36cfc3e5049b4fea71a2bccb066c by Benjamin Barenblat <bbaren@google.com>:

Check printf format strings in str_format_convert_test

Add ABSL_PRINTF_ATTRIBUTE to appropriate functions in
strings/internal/str_format/convert_test. Correct
TypedFormatConvertTest.Char, which was accidentally passing values of
types larger than int to StrPrint.

PiperOrigin-RevId: 439388148
Change-Id: I6cde4e8e0c6455064138192430f07f4c990be0bc

--
f84b4ab2c3b070c8af0c82742ac7a8a4bf443bca by Derek Mauro <dmauro@google.com>:

Use __builtin_memcmp in the absl::string_view implementation
starting with MSVC 16.9, where it first appeared

This enables more constexpr operations

PiperOrigin-RevId: 439317316
Change-Id: Iaf1ce76b60901d4b2d5b96be5900c56572f57b15
GitOrigin-RevId: ef2bf829c333f378ecc12f3259e3187cdb75a3d5

--
afa44fa0245a1cfb1824ef9697b3fa77fa9615c9 by Laramie Leavitt <lar@google.com>:

Comment CMakeLists.txt about internal absl_cc_library() targets.

From what I can tell, these are the CMake targets that are public:

    absl::algorithm
    absl::algorithm_container
    absl::base
    absl::core_headers
    absl::dynamic_annotations
    absl::log_severity
    absl::cleanup
    absl::btree
    absl::fixed_array
    absl::flat_hash_map
    absl::flat_hash_set
    absl::inlined_vector
    absl::node_hash_map
    absl::node_hash_set
    absl::debugging
    absl::failure_signal_handler
    absl::leak_check
    absl::leak_check_disable
    absl::stacktrace
    absl::symbolize
    absl::flags
    absl::flags_commandlineflag
    absl::flags_config
    absl::flags_marshalling
    absl::flags_parse
    absl::flags_reflection
    absl::flags_usage
    absl::bind_front
    absl::function_ref
    absl::hash
    absl::hash_testing
    absl::memory
    absl::meta
    absl::type_traits
    absl::bits
    absl::int128
    absl::numeric
    absl::numeric_representation
    absl::exponential_biased
    absl::periodic_sampler
    absl::sample_recorder
    absl::random_bit_gen_ref
    absl::random_distributions
    absl::random_mocking_bit_gen
    absl::random_random
    absl::random_seed_gen_exception
    absl::random_seed_sequences
    absl::status
    absl::statusor
    absl::cord
    absl::cord_test_helpers
    absl::str_format
    absl::strings
    absl::synchronization
    absl::civil_time
    absl::time
    absl::time_zone
    absl::any
    absl::bad_any_cast
    absl::bad_optional_access
    absl::bad_variant_access
    absl::compare
    absl::optional
    absl::span
    absl::variant
    absl::utility

PiperOrigin-RevId: 438702788
Change-Id: Icf611c35e88f03cd2493a95f61617605305d4e8e

--
a99f60847578e6c0df6befadb29a01c86def0d21 by Abseil Team <absl-team@google.com>:

Internal change

PiperOrigin-RevId: 438647928
Change-Id: I141eadd17d6e8607df25ebc893aecefa0239a72f

--
b23e77e8f62a77023188594390c9e491c507d22c by Abseil Team <absl-team@google.com>:

Internal change

PiperOrigin-RevId: 438628502
Change-Id: I40c4297716c8c1621ba8b02a22393bfcbefb5b5e
GitOrigin-RevId: afa44fa0245a1cfb1824ef9697b3fa77fa9615c9

--
b984c7c1cbee4253192c833046bfcfa16dca8ccf by Dino Radakovic <dinor@google.com>:

Restrict visibility of absl/flags:commandlineflag_internal

PiperOrigin-RevId: 438591894
Change-Id: I12a6392b2c7f9f1263c741dfd6c43ae22e903aad

--
81315601aab70bb6ac2d17655a727d7f9ee2ff95 by Justin Lebar <jlebar@google.com>:

Update example in str_join.h to use a lambda.

PiperOrigin-RevId: 438390035
Change-Id: Icc707b972e5a369a71ad774004fdf0a17a9b33a7

--
1c3c7921224e505faca8617b073f657d3737219f by Dino Radakovic <dinor@google.com>:

Internal change

PiperOrigin-RevId: 438386036
Change-Id: I6066da1b5a1ddf5af265944a31ed298297b4f2e1

--
2d6885f78481f04e0e7ee86060aec15b677144f3 by Abseil Team <absl-team@google.com>:

Internal change

PiperOrigin-RevId: 438378389
Change-Id: If70dd9114114eb44e85afccd521e7fb7e1436b88

--
7f8282ddee7fcd032e01cbfe65c11c2d166cceb8 by Derek Mauro <dmauro@google.com>:

Internal change

PiperOrigin-RevId: 438374554
Change-Id: I993367952af1dc83bd5aa0ae19a64c024f457fdd

--
ce65ba28f6031e45db8fa5118a05410f5166fd7a by Abseil Team <absl-team@google.com>:

Spelling gardening: Heterogeneous has an "e" after the "n".

PiperOrigin-RevId: 438374411
Change-Id: If1a9098a5d04338837998883739c7b555efa62b4
GitOrigin-RevId: b984c7c1cbee4253192c833046bfcfa16dca8ccf

uclibc-ng doesn't provide getauxval which results in the following build
failure on arm or ppc with any user of abseil-cpp such as grpc:

/home/buildroot/autobuild/instance-0/output-1/host/opt/ext-toolchain/bin/../lib/gcc/arm-buildroot-linux-uclibcgnueabi/10.3.0/../../../../arm-buildroot-linux-uclibcgnueabi/bin/ld: /home/buildroot/autobuild/instance-0/output-1/host/arm-buildroot-linux-uclibcgnueabi/sysroot/usr/lib/libabsl_random_internal_randen_hwaes.so.2111.0.0: undefined reference to `getauxval'

To fix this build failure, check that __UCLIBC__ is not defined before
using getauxval (as Babel is not able to check function availability)

Fixes:
 - http://autobuild.buildroot.org/results/775f3ca3dedebff29e212b29dfa896b7613b7a02

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>

--
fb671efb2a70f452f17a884b17cf18817b977a8f by Abseil Team <absl-team@google.com>:

Remove extra semicolon in ABSL_INTERNAL_ASSERT_IS_FULL macro

To fix compilation when empty statement warning is treated as error.

PiperOrigin-RevId: 438342663
Change-Id: I3067fbeffa2691888f37554e88f229f24fb55ecc

--
a58c9396f1d88d11347aed36ef2e1b633071363c by Martijn Vels <mvels@google.com>:

Fix kMaxHeight bounds to kMaxDepth for CordrepBtreeNavigator

Added unit test (confirmed failure mode with old code) and extra assertion in the implementation.

PiperOrigin-RevId: 438327463
Change-Id: I32242c86b0c879b8a42cb9a92075e537d588e09f

--
f348e85dbfc9187ef59085fa2b999374f1670338 by Jorge Gorbe Moya <jgorbe@google.com>:

Make the flags enum in `RefcountAndFlags` a named enum to workaround an lldb
issue (https://github.com/llvm/llvm-project/issues/54602).

PiperOrigin-RevId: 438146097
Change-Id: Ibc2ee26489d99de515a779a903b6458dd0befef7

--
a960a3e9fb2a2e3418f806178e73d8566b78bc85 by Gennadiy Rozental <rogeeff@google.com>:

Introduce support for std::optional<T>/absl::optional<T> flag types.

PiperOrigin-RevId: 438129500
Change-Id: I3d925c0a7f9ce9f857277fac3b0bf664ccd3a95c
GitOrigin-RevId: fb671efb2a70f452f17a884b17cf18817b977a8f

--
291f7ef542f73e4801ab5108014bc02344ef31df by Derek Mauro <dmauro@google.com>:

Internal change

PiperOrigin-RevId: 437835981
Change-Id: I42fd92e74903894533ac9984d7f622e3ba20f468

--
2e8caf1a57c50b518e05b4bca48e4fe1bb19af82 by Andy Getzendanner <durandal@google.com>:

Internal change

PiperOrigin-RevId: 437832673
Change-Id: I61b35089418d01a54cecf161b254b68252bebff3

--
b927482ccc399f7e337b60582988b914d9946e4e by Derek Mauro <dmauro@google.com>:

Simplify endian intrinsics for modern compilers

All modern compilers have either __builtin_bswapN (gcc, clang) or
_byteswap_TYPE (MSVC).  The other intrinsic definitions are no longer
necessary.

PiperOrigin-RevId: 437772295
Change-Id: Ifb3d88ba24b9097f87ceb202272b36d2f5e5117f

--
b6782a2247a16d5c14706a74ec577c19963d9f97 by Derek Mauro <dmauro@google.com>:

Internal change

PiperOrigin-RevId: 437373174
Change-Id: I0f77e1780dee90d7a3c32a08d96c4aeb624a57b4

--
a53e0c724e37b0b01515a99bd25394b8e21ffdfc by Derek Mauro <dmauro@google.com>:

Unify detection of SSE2 and SSSE3 instruction sets and
include the proper headers

Fix the intrinsic implementation of FastHexToBufferZeroPad16 in
numbers.h which only relies on SSSE3, not SSE 4.2.
https://godbolt.org/z/Pf5bn1Yv9

Closes #639

PiperOrigin-RevId: 437286940
Change-Id: Ic97948399b61b91e9c0bccd09313b795b904d714

--
f173f597cb2a75ef2a989f45a496334b85e6f40d by Abseil Team <absl-team@google.com>:

Change assertion function to enable clearer error messages.

PiperOrigin-RevId: 437227057
Change-Id: If420d2f63b51feef6648762f344d5be012cd9c85
GitOrigin-RevId: 291f7ef542f73e4801ab5108014bc02344ef31df

--
8c9dd24a6fbf9ed10ae81f9fa0bc2168558a9700 by Abseil Team <absl-team@google.com>:

Improve WebAssembly detection when using Bazel.

Unfortunately, the --cpu values are not standardized, and both
--cpu=wasm and --cpu=wasm32 are used in the wild. Most notably,
Emscripten's Bazel rules use --cpu=wasm, which was missing.

While there, add support for @platforms//cpu:{wasm32,wasm64}.

This change adds a dependency on @bazel_skylib, which requires
adding the following http_archive() rule to the WORKSPACE file:

  http_archive(
    name = "bazel_skylib",
    urls = ["https://github.com/bazelbuild/bazel-skylib/releases/download/1.2.1/bazel-skylib-1.2.1.tar.gz"],
    sha256 = "f7be3474d42aae265405a592bb7da8e171919d74c16f082a5457840f06054728",
  )

PiperOrigin-RevId: 436815546
Change-Id: I4e1946070c6964abb12259f25a546f2d24e0992a

--
59514589043d9b0734a01f7aa7bc354f5b495eab by Abseil Team <absl-team@google.com>:

Fix some typos that slipped through.

PiperOrigin-RevId: 436777566
Change-Id: Ibf5c54e2671c749dc87d2bd5d36dcd220ce347d4
GitOrigin-RevId: 8c9dd24a6fbf9ed10ae81f9fa0bc2168558a9700

--
bcd349230e418f5e29d5fced1b942828fa5cb2ad by Abseil Team <absl-team@google.com>:

Import of CCTZ from GitHub.

PiperOrigin-RevId: 436317331
Change-Id: I0f8a0c4cd0d5f348a33e486c85c863072c30742a
GitOrigin-RevId: bcd349230e418f5e29d5fced1b942828fa5cb2ad

--
f3ac7ee28fc7de737bc9e2e1d10ff7739781d645 by Gennadiy Rozental <rogeeff@google.com>:

Internal change

PiperOrigin-RevId: 435739199
Change-Id: I8f854b742418a237f9060e4b9f23d0f20baf0bdf

--
fe1329708cb40da8e72e53e4eaad79112bdb79ea by Abseil Team <absl-team@google.com>:

Port SwissTable internals comments from github.com/google/cwisstable to Abseil.

PiperOrigin-RevId: 435719801
Change-Id: I2270cc93aaa5d3d57954a8cea7e570b72b6c3956

--
a6e6fcd4b944ce370ac3307e848645c27bf21e47 by Derek Mauro <dmauro@google.com>:

Internal change

PiperOrigin-RevId: 435716325
Change-Id: I77999f69e176ee6c0d18e7c3329a7c336164f0fc
GitOrigin-RevId: f3ac7ee28fc7de737bc9e2e1d10ff7739781d645