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author | 2020-10-19 15:25:26 -0700 | |
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committer | 2020-10-19 19:24:23 -0400 | |
commit | 4b915e70929ca2d6152240facc83d3d38c5d5f28 (patch) | |
tree | 3663ad6f3ddb8f0a94045bac592901ee7298447e /absl/strings/internal/cord_internal.h | |
parent | 8f1c34a77a2ba04512b7f9cbc6013d405e6a0b31 (diff) |
Export of internal Abseil changes
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77c85460dc3c46593b231c5161ac55273bb0c7ef by Abseil Team <absl-team@google.com>:
Support int128 in SimpleAtoi.
PiperOrigin-RevId: 337946262
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0be53049ccf8309650e4e22f23b290e5f75ee828 by Gennadiy Rozental <rogeeff@google.com>:
Update build scripts to use --mount instead of --volume to mount the host data into a container.
This is somewhat more verbose, but more readable and flexible. More importantly this is what docker documentation is recomending to use now.
PiperOrigin-RevId: 337898761
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3bc877f1679fdf61ecbf4365287a0403cfc9b53e by Samuel Benzaquen <sbenza@google.com>:
Add Cord constructor for constinit instances.
PiperOrigin-RevId: 337871148
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8b87701892b9c325e78ad4e8e4f16b785a744622 by Chris Kennelly <ckennelly@google.com>:
Use the address of kSeed, rather than its value.
We initialize kSeed with &kSeed, so these are equivalent, but kSeed requires a
load from memory while &kSeed can be formed as a RIP-relative lea.
PiperOrigin-RevId: 337868415
GitOrigin-RevId: 77c85460dc3c46593b231c5161ac55273bb0c7ef
Change-Id: I3d06c18a123f1be29dad5801e8625952dc41cd95
Diffstat (limited to 'absl/strings/internal/cord_internal.h')
-rw-r--r-- | absl/strings/internal/cord_internal.h | 82 |
1 files changed, 70 insertions, 12 deletions
diff --git a/absl/strings/internal/cord_internal.h b/absl/strings/internal/cord_internal.h index 00b9baa9..aa91a691 100644 --- a/absl/strings/internal/cord_internal.h +++ b/absl/strings/internal/cord_internal.h @@ -33,14 +33,17 @@ namespace cord_internal { // Wraps std::atomic for reference counting. class Refcount { public: - Refcount() : count_{1} {} - ~Refcount() {} + constexpr Refcount() : count_{kRefIncrement} {} + struct Immortal {}; + explicit constexpr Refcount(Immortal) : count_(kImmortalTag) {} - // Increments the reference count by 1. Imposes no memory ordering. - inline void Increment() { count_.fetch_add(1, std::memory_order_relaxed); } + // Increments the reference count. Imposes no memory ordering. + inline void Increment() { + count_.fetch_add(kRefIncrement, std::memory_order_relaxed); + } // Asserts that the current refcount is greater than 0. If the refcount is - // greater than 1, decrements the reference count by 1. + // greater than 1, decrements the reference count. // // Returns false if there are no references outstanding; true otherwise. // Inserts barriers to ensure that state written before this method returns @@ -48,19 +51,24 @@ class Refcount { // false. inline bool Decrement() { int32_t refcount = count_.load(std::memory_order_acquire); - assert(refcount > 0); - return refcount != 1 && count_.fetch_sub(1, std::memory_order_acq_rel) != 1; + assert(refcount > 0 || refcount & kImmortalTag); + return refcount != kRefIncrement && + count_.fetch_sub(kRefIncrement, std::memory_order_acq_rel) != + kRefIncrement; } // Same as Decrement but expect that refcount is greater than 1. inline bool DecrementExpectHighRefcount() { - int32_t refcount = count_.fetch_sub(1, std::memory_order_acq_rel); - assert(refcount > 0); - return refcount != 1; + int32_t refcount = + count_.fetch_sub(kRefIncrement, std::memory_order_acq_rel); + assert(refcount > 0 || refcount & kImmortalTag); + return refcount != kRefIncrement; } // Returns the current reference count using acquire semantics. - inline int32_t Get() const { return count_.load(std::memory_order_acquire); } + inline int32_t Get() const { + return count_.load(std::memory_order_acquire) >> kImmortalShift; + } // Returns whether the atomic integer is 1. // If the reference count is used in the conventional way, a @@ -70,9 +78,27 @@ class Refcount { // performs the memory barrier needed for the owning thread // to act on the object, knowing that it has exclusive access to the // object. - inline bool IsOne() { return count_.load(std::memory_order_acquire) == 1; } + inline bool IsOne() { + return count_.load(std::memory_order_acquire) == kRefIncrement; + } + + bool IsImmortal() const { + return (count_.load(std::memory_order_relaxed) & kImmortalTag) != 0; + } private: + // We reserve the bottom bit to tag a reference count as immortal. + // By making it `1` we ensure that we never reach `0` when adding/subtracting + // `2`, thus it never looks as if it should be destroyed. + // These are used for the StringConstant constructor where we do not increase + // the refcount at construction time (due to constinit requirements) but we + // will still decrease it at destruction time to avoid branching on Unref. + enum { + kImmortalShift = 1, + kRefIncrement = 1 << kImmortalShift, + kImmortalTag = kRefIncrement - 1 + }; + std::atomic<int32_t> count_; }; @@ -97,6 +123,10 @@ enum CordRepKind { }; struct CordRep { + CordRep() = default; + constexpr CordRep(Refcount::Immortal immortal, size_t l) + : length(l), refcount(immortal), tag(EXTERNAL), data{} {} + // The following three fields have to be less than 32 bytes since // that is the smallest supported flat node size. size_t length; @@ -135,6 +165,12 @@ using ExternalReleaserInvoker = void (*)(CordRepExternal*); // External CordReps are allocated together with a type erased releaser. The // releaser is stored in the memory directly following the CordRepExternal. struct CordRepExternal : public CordRep { + CordRepExternal() = default; + explicit constexpr CordRepExternal(absl::string_view str) + : CordRep(Refcount::Immortal{}, str.size()), + base(str.data()), + releaser_invoker(nullptr) {} + const char* base; // Pointer to function that knows how to call and destroy the releaser. ExternalReleaserInvoker releaser_invoker; @@ -178,6 +214,14 @@ struct CordRepExternalImpl } }; +template <typename Str> +struct ConstInitExternalStorage { + ABSL_CONST_INIT static CordRepExternal value; +}; + +template <typename Str> +CordRepExternal ConstInitExternalStorage<Str>::value(Str::value); + enum { kMaxInline = 15, // Tag byte & kMaxInline means we are storing a pointer. @@ -195,9 +239,23 @@ struct AsTree { char padding[kMaxInline + 1 - sizeof(absl::cord_internal::CordRep*) - 1]; char tagged_size; }; + +constexpr char GetOrNull(absl::string_view data, size_t pos) { + return pos < data.size() ? data[pos] : '\0'; +} + union InlineData { constexpr InlineData() : as_chars{} {} explicit constexpr InlineData(AsTree tree) : as_tree(tree) {} + explicit constexpr InlineData(absl::string_view chars) + : as_chars{GetOrNull(chars, 0), GetOrNull(chars, 1), + GetOrNull(chars, 2), GetOrNull(chars, 3), + GetOrNull(chars, 4), GetOrNull(chars, 5), + GetOrNull(chars, 6), GetOrNull(chars, 7), + GetOrNull(chars, 8), GetOrNull(chars, 9), + GetOrNull(chars, 10), GetOrNull(chars, 11), + GetOrNull(chars, 12), GetOrNull(chars, 13), + GetOrNull(chars, 14), static_cast<char>(chars.size())} {} AsTree as_tree; char as_chars[kMaxInline + 1]; |