Export of internal Abseil changes

--
d6748c733a70cd74ad9b76a0c9cd6b3fe2cecacf by Xiaoyi Zhang <zhangxy@google.com>:

Remove empty block, to address alerts reported in
#368.

PiperOrigin-RevId: 265099887

--
232e2036b5668d6d1296b881f9347756d84541ee by Derek Mauro <dmauro@google.com>:

Make the Linux Bazel CI scripts test with the exception mode explicitly set.

PiperOrigin-RevId: 265092105

--
942a40696c2c9b833be03e92d22a6ede7bccb6d4 by Xiaoyi Zhang <zhangxy@google.com>:

Import #372.
Suppress the unused variable warning on GCC, i.e. "-Wunused-variable".

PiperOrigin-RevId: 265063925

--
7ef90796b52cbdc260afc77cf47206f9356471d0 by Xiaoyi Zhang <zhangxy@google.com>:

Add quotes to `ABSL_COMMON_INCLUDE_DIRS` since it's a list and may contain a
`;`. This addresses #373.

PiperOrigin-RevId: 265059077

--
43f3ae742e00b83672ad6c5bc5b17fdb8f9fe6fe by Gennadiy Rozental <rogeeff@google.com>:

Internal re-organization

PiperOrigin-RevId: 264913945

--
6a2adf9c08ee1d98cc6b2855a676345c6495294a by Andy Soffer <asoffer@google.com>:

Publicly expose type names for uniform interval tags as in, for example, absl::IntervalClosedClosedTag, and add equality comparison operators.

PiperOrigin-RevId: 264861162

--
3c90c6e05fd61d56b419cd2d39dab8f17b8711b8 by Abseil Team <absl-team@google.com>:

Add validity check on returned frame pointer.

PiperOrigin-RevId: 264858823

--
2db87e0cfa0c6bea7ba81684b834cb8a73b7d748 by Gennadiy Rozental <rogeeff@google.com>:

Add MUST_USE_RESULT attribute to absl::GetFlag to prevent accidental misuse.

PiperOrigin-RevId: 264782762
GitOrigin-RevId: d6748c733a70cd74ad9b76a0c9cd6b3fe2cecacf
Change-Id: I169e9c5358e4f63000c1255e806d26b8afecf5ff

CMake/AbseilHelpers.cmake

@@ -108,7 +108,7 @@ function(absl_cc_library)
       target_sources(${_NAME} PRIVATE ${ABSL_CC_LIB_SRCS} ${ABSL_CC_LIB_HDRS})
       target_include_directories(${_NAME}
         PUBLIC
-          $<BUILD_INTERFACE:${ABSL_COMMON_INCLUDE_DIRS}>
+          "$<BUILD_INTERFACE:${ABSL_COMMON_INCLUDE_DIRS}>"
           $<INSTALL_INTERFACE:${ABSL_INSTALL_INCLUDEDIR}>
       )
       target_compile_options(${_NAME}
@@ -145,7 +145,7 @@ function(absl_cc_library)
       add_library(${_NAME} INTERFACE)
       target_include_directories(${_NAME}
         INTERFACE
-          $<BUILD_INTERFACE:${ABSL_COMMON_INCLUDE_DIRS}>
+          "$<BUILD_INTERFACE:${ABSL_COMMON_INCLUDE_DIRS}>"
           $<INSTALL_INTERFACE:${ABSL_INSTALL_INCLUDEDIR}>
         )
       target_link_libraries(${_NAME}

absl/base/internal/spinlock.h

@@ -225,11 +225,10 @@ inline uint32_t SpinLock::TryLockInternal(uint32_t lock_value,
     }
   }
 
-  if (lockword_.compare_exchange_strong(
+  if (!lockword_.compare_exchange_strong(
           lock_value,
           kSpinLockHeld | lock_value | wait_cycles | sched_disabled_bit,
           std::memory_order_acquire, std::memory_order_relaxed)) {
-  } else {
     base_internal::SchedulingGuard::EnableRescheduling(sched_disabled_bit != 0);
   }
 

absl/debugging/internal/stacktrace_x86-inl.inc

@@ -36,6 +36,8 @@
 
 #include "absl/base/internal/raw_logging.h"
 
+using absl::debugging_internal::AddressIsReadable;
+
 #if defined(__linux__) && defined(__i386__)
 // Count "push %reg" instructions in VDSO __kernel_vsyscall(),
 // preceeding "syscall" or "sysenter".
@@ -81,7 +83,7 @@ static int CountPushInstructions(const unsigned char *const addr) {
       // "mov reg,reg"
       if (addr[i + 1] == 0xE5) {
         // Found "mov %esp,%ebp".
-        return 0;  
+        return 0;
       }
       ++i;  // Skip register encoding byte.
     } else if (addr[i] == 0x0F &&
@@ -222,7 +224,7 @@ static void **NextStackFrame(void **old_fp, const void *uc) {
           // "double fault" in case we hit the first fault due to e.g. stack
           // corruption.
           void *const reg_esp2 = reg_esp[num_push_instructions - 1];
-          if (absl::debugging_internal::AddressIsReadable(reg_esp2)) {
+          if (AddressIsReadable(reg_esp2)) {
             // Alleged %esp is readable, use it for further unwinding.
             new_fp = reinterpret_cast<void **>(reg_esp2);
           }
@@ -274,7 +276,7 @@ static void **NextStackFrame(void **old_fp, const void *uc) {
     // Note: NextStackFrame<false>() is only called while the program
     //       is already on its last leg, so it's ok to be slow here.
 
-    if (!absl::debugging_internal::AddressIsReadable(new_fp)) {
+    if (!AddressIsReadable(new_fp)) {
       return nullptr;
     }
   }

absl/flags/BUILD.bazel

@@ -136,6 +136,7 @@ cc_library(
     name = "flag",
     srcs = [
         "flag.cc",
+        "internal/flag.cc",
     ],
     hdrs = [
         "declare.h",
@@ -152,6 +153,7 @@ cc_library(
         "//absl/base",
         "//absl/base:core_headers",
         "//absl/strings",
+        "//absl/synchronization",
     ],
 )
 

absl/flags/CMakeLists.txt

@@ -120,6 +120,7 @@ absl_cc_library(
     flags
   SRCS
     "flag.cc"
+    "internal/flag.cc"
   HDRS
     "declare.h"
     "flag.h"
@@ -136,6 +137,7 @@ absl_cc_library(
     absl::base
     absl::core_headers
     absl::strings
+    absl::synchronization
 )
 
 # Internal-only target, do not depend on directly.

absl/flags/declare.h

@@ -39,8 +39,13 @@ class Flag;
 // Flag
 //
 // Forward declaration of the `absl::Flag` type for use in defining the macro.
+#if defined(_MSC_VER)
+template <typename T>
+class Flag;
+#else
 template <typename T>
 using Flag = flags_internal::Flag<T>;
+#endif
 
 }  // namespace absl
 

absl/flags/flag.cc

@@ -41,4 +41,20 @@ ABSL_FLAGS_INTERNAL_FOR_EACH_LOCK_FREE(ABSL_FLAGS_ATOMIC_GET)
 
 #undef ABSL_FLAGS_ATOMIC_GET
 
+// This global nutex protects on-demand construction of flag objects in MSVC
+// builds.
+#if defined(_MSC_VER)
+
+namespace flags_internal {
+
+ABSL_CONST_INIT static absl::Mutex construction_guard(absl::kConstInit);
+
+void LockGlobalConstructionGuard() { construction_guard.Lock(); }
+
+void UnlockGlobalConstructionGuard() { construction_guard.Unlock(); }
+
+}  // namespace flags_internal
+
+#endif
+
 }  // namespace absl

absl/flags/flag.h

@@ -63,8 +63,100 @@ namespace absl {
 //      ABSL_FLAG(int, count, 0, "Count of items to process");
 //
 // No public methods of `absl::Flag<T>` are part of the Abseil Flags API.
+#if !defined(_MSC_VER)
 template <typename T>
 using Flag = flags_internal::Flag<T>;
+#else
+// MSVC debug builds do not implement constexpr correctly for classes with
+// virtual methods. To work around this we adding level of indirection, so that
+// the class `absl::Flag` contains an `internal::Flag*` (instead of being an
+// alias to that class) and dynamically allocates an instance when necessary.
+// We also forward all calls to internal::Flag methods via trampoline methods.
+// In this setup the `absl::Flag` class does not have virtual methods and thus
+// MSVC is able to initialize it at link time. To deal with multiple threads
+// accessing the flag for the first time concurrently we use an atomic boolean
+// indicating if flag object is constructed. We also employ the double-checked
+// locking pattern where the second level of protection is a global Mutex, so
+// if two threads attempt to construct the flag concurrently only one wins.
+
+namespace flags_internal {
+void LockGlobalConstructionGuard();
+void UnlockGlobalConstructionGuard();
+}  // namespace flags_internal
+
+template <typename T>
+class Flag {
+ public:
+  constexpr Flag(const char* name, const flags_internal::HelpGenFunc help_gen,
+                 const char* filename,
+                 const flags_internal::FlagMarshallingOpFn marshalling_op,
+                 const flags_internal::InitialValGenFunc initial_value_gen)
+      : name_(name),
+        help_gen_(help_gen),
+        filename_(filename),
+        marshalling_op_(marshalling_op),
+        initial_value_gen_(initial_value_gen),
+        inited_(false) {}
+
+  flags_internal::Flag<T>* GetImpl() const {
+    if (!inited_.load(std::memory_order_acquire)) {
+      flags_internal::LockGlobalConstructionGuard();
+
+      if (inited_.load(std::memory_order_acquire)) {
+        return impl_;
+      }
+
+      impl_ = new flags_internal::Flag<T>(name_, help_gen_, filename_,
+                                          marshalling_op_, initial_value_gen_);
+      inited_.store(true, std::memory_order_release);
+
+      flags_internal::UnlockGlobalConstructionGuard();
+    }
+
+    return impl_;
+  }
+
+  // absl::Flag API
+  bool IsRetired() const { return GetImpl()->IsRetired(); }
+  bool IsAbseilFlag() const { return GetImpl()->IsAbseilFlag(); }
+  absl::string_view Name() const { return GetImpl()->Name(); }
+  std::string Help() const { return GetImpl()->Help(); }
+  bool IsModified() const { return GetImpl()->IsModified(); }
+  void SetModified(bool is_modified) { GetImpl()->SetModified(is_modified); }
+  bool IsSpecifiedOnCommandLine() const {
+    GetImpl()->IsSpecifiedOnCommandLine();
+  }
+  absl::string_view Typename() const { return GetImpl()->Typename(); }
+  std::string Filename() const { return GetImpl()->Filename(); }
+  std::string DefaultValue() const { return GetImpl()->DefaultValue(); }
+  std::string CurrentValue() const { return GetImpl()->CurrentValue(); }
+  bool HasValidatorFn() const { return GetImpl()->HasValidatorFn(); }
+  bool InvokeValidator(const void* value) const {
+    return GetImpl()->InvokeValidator(value);
+  }
+  template <typename T>
+  inline bool IsOfType() const {
+    return GetImpl()->IsOftype<T>();
+  }
+  T Get() const { return GetImpl()->Get(); }
+  bool AtomicGet(T* v) const { return GetImpl()->AtomicGet(v); }
+  void Set(const T& v) { GetImpl()->Set(v); }
+  void SetCallback(const flags_internal::FlagCallback mutation_callback) {
+    GetImpl()->SetCallback(mutation_callback);
+  }
+  void InvokeCallback() { GetImpl()->InvokeCallback(); }
+
+ private:
+  const char* name_;
+  const flags_internal::HelpGenFunc help_gen_;
+  const char* filename_;
+  const flags_internal::FlagMarshallingOpFn marshalling_op_;
+  const flags_internal::InitialValGenFunc initial_value_gen_;
+
+  mutable std::atomic<bool> inited_;
+  mutable flags_internal::Flag<T>* impl_ = nullptr;
+};
+#endif
 
 // GetFlag()
 //
@@ -83,7 +175,7 @@ using Flag = flags_internal::Flag<T>;
 //   // FLAGS_firstname is a Flag of type `std::string`
 //   std::string first_name = absl::GetFlag(FLAGS_firstname);
 template <typename T>
-T GetFlag(const absl::Flag<T>& flag) {
+ABSL_MUST_USE_RESULT T GetFlag(const absl::Flag<T>& flag) {
 #define ABSL_FLAGS_INTERNAL_LOCK_FREE_VALIDATE(BIT) \
   static_assert(                                    \
       !std::is_same<T, BIT>::value,                 \
@@ -96,7 +188,7 @@ T GetFlag(const absl::Flag<T>& flag) {
 
 // Overload for `GetFlag()` for types that support lock-free reads.
 #define ABSL_FLAGS_INTERNAL_LOCK_FREE_EXPORT(T) \
-  extern T GetFlag(const absl::Flag<T>& flag);
+  ABSL_MUST_USE_RESULT T GetFlag(const absl::Flag<T>& flag);
 ABSL_FLAGS_INTERNAL_FOR_EACH_LOCK_FREE(ABSL_FLAGS_INTERNAL_LOCK_FREE_EXPORT)
 #undef ABSL_FLAGS_INTERNAL_LOCK_FREE_EXPORT
 
@@ -184,13 +276,23 @@ void SetFlag(absl::Flag<T>* flag, const V& v) {
 #if ABSL_FLAGS_STRIP_NAMES
 #define ABSL_FLAG_IMPL_FLAGNAME(txt) ""
 #define ABSL_FLAG_IMPL_FILENAME() ""
+#if !defined(_MSC_VER)
 #define ABSL_FLAG_IMPL_REGISTRAR(T, flag) \
   absl::flags_internal::FlagRegistrar<T, false>(&flag)
 #else
+#define ABSL_FLAG_IMPL_REGISTRAR(T, flag) \
+  absl::flags_internal::FlagRegistrar<T, false>(flag.GetImpl())
+#endif
+#else
 #define ABSL_FLAG_IMPL_FLAGNAME(txt) txt
 #define ABSL_FLAG_IMPL_FILENAME() __FILE__
+#if !defined(_MSC_VER)
 #define ABSL_FLAG_IMPL_REGISTRAR(T, flag) \
   absl::flags_internal::FlagRegistrar<T, true>(&flag)
+#else
+#define ABSL_FLAG_IMPL_REGISTRAR(T, flag) \
+  absl::flags_internal::FlagRegistrar<T, true>(flag.GetImpl())
+#endif
 #endif
 
 // ABSL_FLAG_IMPL macro definition conditional on ABSL_FLAGS_STRIP_HELP

absl/flags/internal/commandlineflag.cc

@@ -68,7 +68,7 @@ absl::Mutex* InitFlag(CommandLineFlag* flag) {
   {
     absl::MutexLock lock(mu);
 
-    if (!flag->retired && flag->def == nullptr) {
+    if (!flag->IsRetired() && flag->def == nullptr) {
       // Need to initialize def and cur fields.
       flag->def = (*flag->make_init_value)();
       flag->cur = Clone(flag->op, flag->def);
@@ -94,16 +94,6 @@ absl::Mutex* CommandLineFlag::InitFlagIfNecessary() const
   return &this->locks->primary_mu;
 }
 
-void CommandLineFlag::Destroy() const {
-  // Values are heap allocated for retired and Abseil Flags.
-  if (IsRetired() || IsAbseilFlag()) {
-    if (this->cur) Delete(this->op, this->cur);
-    if (this->def) Delete(this->op, this->def);
-  }
-
-  delete this->locks;
-}
-
 bool CommandLineFlag::IsModified() const {
   absl::MutexLock l(InitFlagIfNecessary());
   return modified;
@@ -159,87 +149,6 @@ std::string CommandLineFlag::CurrentValue() const {
   return Unparse(this->marshalling_op, this->cur);
 }
 
-bool CommandLineFlag::HasValidatorFn() const {
-  absl::MutexLock l(InitFlagIfNecessary());
-
-  return this->validator != nullptr;
-}
-
-bool CommandLineFlag::SetValidatorFn(FlagValidator fn) {
-  absl::MutexLock l(InitFlagIfNecessary());
-
-  // ok to register the same function over and over again
-  if (fn == this->validator) return true;
-
-  // Can't set validator to a different function, unless reset first.
-  if (fn != nullptr && this->validator != nullptr) {
-    ABSL_INTERNAL_LOG(
-        WARNING, absl::StrCat("Ignoring SetValidatorFn() for flag '", Name(),
-                              "': validate-fn already registered"));
-
-    return false;
-  }
-
-  this->validator = fn;
-  return true;
-}
-
-bool CommandLineFlag::InvokeValidator(const void* value) const
-    EXCLUSIVE_LOCKS_REQUIRED(this->locks->primary_mu) {
-  if (!this->validator) {
-    return true;
-  }
-
-  (void)value;
-
-  ABSL_INTERNAL_LOG(
-      FATAL,
-      absl::StrCat("Flag '", Name(),
-                   "' of encapsulated type should not have a validator"));
-
-  return false;
-}
-
-void CommandLineFlag::SetCallback(
-    const flags_internal::FlagCallback mutation_callback) {
-  absl::MutexLock l(InitFlagIfNecessary());
-
-  callback = mutation_callback;
-
-  InvokeCallback();
-}
-
-// If the flag has a mutation callback this function invokes it. While the
-// callback is being invoked the primary flag's mutex is unlocked and it is
-// re-locked back after call to callback is completed. Callback invocation is
-// guarded by flag's secondary mutex instead which prevents concurrent callback
-// invocation. Note that it is possible for other thread to grab the primary
-// lock and update flag's value at any time during the callback invocation.
-// This is by design. Callback can get a value of the flag if necessary, but it
-// might be different from the value initiated the callback and it also can be
-// different by the time the callback invocation is completed.
-// Requires that *primary_lock be held in exclusive mode; it may be released
-// and reacquired by the implementation.
-void CommandLineFlag::InvokeCallback()
-    EXCLUSIVE_LOCKS_REQUIRED(this->locks->primary_mu) {
-  if (!this->callback) return;
-
-  // The callback lock is guaranteed initialized, because *locks->primary_mu
-  // exists.
-  absl::Mutex* callback_mu = &this->locks->callback_mu;
-
-  // When executing the callback we need the primary flag's mutex to be unlocked
-  // so that callback can retrieve the flag's value.
-  this->locks->primary_mu.Unlock();
-
-  {
-    absl::MutexLock lock(callback_mu);
-    this->callback();
-  }
-
-  this->locks->primary_mu.Lock();
-}
-
 // Attempts to parse supplied `value` string using parsing routine in the `flag`
 // argument. If parsing is successful, it will try to validate that the parsed
 // value is valid for the specified 'flag'. Finally this function stores the