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Add GetCustomAppendBuffer method to absl::Cord

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The Cord::GetCustomAppendBuffer() method provides the same functionality as Cord::GetAppendBuffer(), except that callers can specify a custom block size/limit if the method returns a newly allocated buffer.

In other words: Cord::GetAppendBuffer() defaults to CordBuffer::CreateWithDefaultLimit(), Cord::GetCustomAppendBuffer() defaults to CordBuffer::CreateWithCustomLimit().

PiperOrigin-RevId: 461231989
Change-Id: I5c03f31139d9b068feee1bea76d59e1c5e30ef07
pull/1223/head
Martijn Vels 3 years ago committed by Copybara-Service
parent d6f96eda14
commit b707b6c179
3 changed files with 90 additions and 29 deletions
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  1. 18
      absl/strings/cord.cc
  2. 28
      absl/strings/cord.h
  3. 73
      absl/strings/cord_test.cc

18
absl/strings/cord.cc
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@ -537,18 +537,23 @@ static CordRep::ExtractResult ExtractAppendBuffer(CordRep* rep,
}
}
static CordBuffer CreateAppendBuffer(InlineData& data, size_t capacity) {
static CordBuffer CreateAppendBuffer(InlineData& data, size_t block_size,
size_t capacity) {
// Watch out for overflow, people can ask for size_t::max().
const size_t size = data.inline_size();
capacity = (std::min)(std::numeric_limits<size_t>::max() - size, capacity);
CordBuffer buffer = CordBuffer::CreateWithDefaultLimit(size + capacity);
const size_t max_capacity = std::numeric_limits<size_t>::max() - size;
capacity = (std::min)(max_capacity, capacity) + size;
CordBuffer buffer =
block_size ? CordBuffer::CreateWithCustomLimit(block_size, capacity)
: CordBuffer::CreateWithDefaultLimit(capacity);
cord_internal::SmallMemmove(buffer.data(), data.as_chars(), size);
buffer.SetLength(size);
data = {};
return buffer;
}
CordBuffer Cord::GetAppendBufferSlowPath(size_t capacity, size_t min_capacity) {
CordBuffer Cord::GetAppendBufferSlowPath(size_t block_size, size_t capacity,
size_t min_capacity) {
auto constexpr method = CordzUpdateTracker::kGetAppendBuffer;
CordRep* tree = contents_.tree();
if (tree != nullptr) {
@ -558,9 +563,10 @@ CordBuffer Cord::GetAppendBufferSlowPath(size_t capacity, size_t min_capacity) {
contents_.SetTreeOrEmpty(result.tree, scope);
return CordBuffer(result.extracted->flat());
}
return CordBuffer::CreateWithDefaultLimit(capacity);
return block_size ? CordBuffer::CreateWithCustomLimit(block_size, capacity)
: CordBuffer::CreateWithDefaultLimit(capacity);
}
return CreateAppendBuffer(contents_.data_, capacity);
return CreateAppendBuffer(contents_.data_, block_size, capacity);
}
void Cord::Append(const Cord& src) {

28
absl/strings/cord.h
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@ -284,6 +284,19 @@ class Cord {
// }
CordBuffer GetAppendBuffer(size_t capacity, size_t min_capacity = 16);
// Returns a CordBuffer, re-using potential existing capacity in this cord.
//
// This function is identical to `GetAppendBuffer`, except that in the case
// where a new `CordBuffer` is allocated, it is allocated using the provided
// custom limit instead of the default limit. `GetAppendBuffer` will default
// to `CordBuffer::CreateWithDefaultLimit(capacity)` whereas this method
// will default to `CordBuffer::CreateWithCustomLimit(block_size, capacity)`.
// This method is equivalent to `GetAppendBuffer` if `block_size` is zero.
// See the documentation for `CreateWithCustomLimit` for more details on the
// restrictions and legal values for `block_size`.
CordBuffer GetCustomAppendBuffer(size_t block_size, size_t capacity,
size_t min_capacity = 16);
// Cord::Prepend()
//
// Prepends data to the Cord, which may come from another Cord or other string
@ -980,7 +993,8 @@ class Cord {
void AppendPrecise(absl::string_view src, MethodIdentifier method);
void PrependPrecise(absl::string_view src, MethodIdentifier method);
CordBuffer GetAppendBufferSlowPath(size_t capacity, size_t min_capacity);
CordBuffer GetAppendBufferSlowPath(size_t block_size, size_t capacity,
size_t min_capacity);
// Prepends the provided data to this instance. `method` contains the public
// API method for this action which is tracked for Cordz sampling purposes.
@ -1360,7 +1374,17 @@ inline void Cord::Prepend(CordBuffer buffer) {
inline CordBuffer Cord::GetAppendBuffer(size_t capacity, size_t min_capacity) {
if (empty()) return CordBuffer::CreateWithDefaultLimit(capacity);
return GetAppendBufferSlowPath(capacity, min_capacity);
return GetAppendBufferSlowPath(0, capacity, min_capacity);
}
inline CordBuffer Cord::GetCustomAppendBuffer(size_t block_size,
size_t capacity,
size_t min_capacity) {
if (empty()) {
return block_size ? CordBuffer::CreateWithCustomLimit(block_size, capacity)
: CordBuffer::CreateWithDefaultLimit(capacity);
}
return GetAppendBufferSlowPath(block_size, capacity, min_capacity);
}
extern template void Cord::Append(std::string&& src);

73
absl/strings/cord_test.cc
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@ -733,18 +733,48 @@ TEST_P(CordTest, PrependLargeBuffer) {
EXPECT_THAT(cord.Chunks(), ::testing::ElementsAre(s2, s1));
}
TEST_P(CordTest, GetAppendBufferOnEmptyCord) {
class CordAppendBufferTest : public testing::TestWithParam<bool> {
public:
size_t is_default() const { return GetParam(); }
// Returns human readable string representation of the test parameter.
static std::string ToString(testing::TestParamInfo<bool> param) {
return param.param ? "DefaultLimit" : "CustomLimit";
}
size_t limit() const {
return is_default() ? absl::CordBuffer::kDefaultLimit
: absl::CordBuffer::kCustomLimit;
}
size_t maximum_payload() const {
return is_default() ? absl::CordBuffer::MaximumPayload()
: absl::CordBuffer::MaximumPayload(limit());
}
absl::CordBuffer GetAppendBuffer(absl::Cord& cord, size_t capacity,
size_t min_capacity = 16) {
return is_default()
? cord.GetAppendBuffer(capacity, min_capacity)
: cord.GetCustomAppendBuffer(limit(), capacity, min_capacity);
}
};
INSTANTIATE_TEST_SUITE_P(WithParam, CordAppendBufferTest, testing::Bool(),
CordAppendBufferTest::ToString);
TEST_P(CordAppendBufferTest, GetAppendBufferOnEmptyCord) {
absl::Cord cord;
absl::CordBuffer buffer = cord.GetAppendBuffer(1000);
absl::CordBuffer buffer = GetAppendBuffer(cord, 1000);
EXPECT_GE(buffer.capacity(), 1000);
EXPECT_EQ(buffer.length(), 0);
}
TEST_P(CordTest, GetAppendBufferOnInlinedCord) {
TEST_P(CordAppendBufferTest, GetAppendBufferOnInlinedCord) {
static constexpr int kInlinedSize = sizeof(absl::CordBuffer) - 1;
for (int size : {6, kInlinedSize - 3, kInlinedSize - 2, 1000}) {
absl::Cord cord("Abc");
absl::CordBuffer buffer = cord.GetAppendBuffer(size, 1);
absl::CordBuffer buffer = GetAppendBuffer(cord, size, 1);
EXPECT_GE(buffer.capacity(), 3 + size);
EXPECT_EQ(buffer.length(), 3);
EXPECT_EQ(absl::string_view(buffer.data(), buffer.length()), "Abc");
@ -752,7 +782,7 @@ TEST_P(CordTest, GetAppendBufferOnInlinedCord) {
}
}
TEST_P(CordTest, GetAppendBufferOnInlinedCordWithCapacityCloseToMax) {
TEST_P(CordAppendBufferTest, GetAppendBufferOnInlinedCordCapacityCloseToMax) {
// Cover the use case where we have a non empty inlined cord with some size
// 'n', and ask for something like 'uint64_max - k', assuming internal logic
// could overflow on 'uint64_max - k + size', and return a valid, but
@ -760,30 +790,31 @@ TEST_P(CordTest, GetAppendBufferOnInlinedCordWithCapacityCloseToMax) {
for (size_t dist_from_max = 0; dist_from_max <= 4; ++dist_from_max) {
absl::Cord cord("Abc");
size_t size = std::numeric_limits<size_t>::max() - dist_from_max;
absl::CordBuffer buffer = cord.GetAppendBuffer(size, 1);
EXPECT_EQ(buffer.capacity(), absl::CordBuffer::kDefaultLimit);
absl::CordBuffer buffer = GetAppendBuffer(cord, size, 1);
EXPECT_GE(buffer.capacity(), maximum_payload());
EXPECT_EQ(buffer.length(), 3);
EXPECT_EQ(absl::string_view(buffer.data(), buffer.length()), "Abc");
EXPECT_TRUE(cord.empty());
}
}
TEST_P(CordTest, GetAppendBufferOnFlat) {
TEST_P(CordAppendBufferTest, GetAppendBufferOnFlat) {
// Create a cord with a single flat and extra capacity
absl::Cord cord;
absl::CordBuffer buffer = absl::CordBuffer::CreateWithDefaultLimit(500);
const size_t expected_capacity = buffer.capacity();
buffer.SetLength(3);
memcpy(buffer.data(), "Abc", 3);
cord.Append(std::move(buffer));
buffer = cord.GetAppendBuffer(6);
EXPECT_GE(buffer.capacity(), 500);
buffer = GetAppendBuffer(cord, 6);
EXPECT_EQ(buffer.capacity(), expected_capacity);
EXPECT_EQ(buffer.length(), 3);
EXPECT_EQ(absl::string_view(buffer.data(), buffer.length()), "Abc");
EXPECT_TRUE(cord.empty());
}
TEST_P(CordTest, GetAppendBufferOnFlatWithoutMinCapacity) {
TEST_P(CordAppendBufferTest, GetAppendBufferOnFlatWithoutMinCapacity) {
// Create a cord with a single flat and extra capacity
absl::Cord cord;
absl::CordBuffer buffer = absl::CordBuffer::CreateWithDefaultLimit(500);
@ -791,13 +822,13 @@ TEST_P(CordTest, GetAppendBufferOnFlatWithoutMinCapacity) {
memset(buffer.data(), 'x', 30);
cord.Append(std::move(buffer));
buffer = cord.GetAppendBuffer(1000, 900);
buffer = GetAppendBuffer(cord, 1000, 900);
EXPECT_GE(buffer.capacity(), 1000);
EXPECT_EQ(buffer.length(), 0);
EXPECT_EQ(cord, std::string(30, 'x'));
}
TEST_P(CordTest, GetAppendBufferOnTree) {
TEST_P(CordAppendBufferTest, GetAppendBufferOnTree) {
RandomEngine rng;
for (int num_flats : {2, 3, 100}) {
// Create a cord with `num_flats` flats and extra capacity
@ -812,7 +843,7 @@ TEST_P(CordTest, GetAppendBufferOnTree) {
memcpy(buffer.data(), last.data(), 10);
cord.Append(std::move(buffer));
}
absl::CordBuffer buffer = cord.GetAppendBuffer(6);
absl::CordBuffer buffer = GetAppendBuffer(cord, 6);
EXPECT_GE(buffer.capacity(), 500);
EXPECT_EQ(buffer.length(), 10);
EXPECT_EQ(absl::string_view(buffer.data(), buffer.length()), last);
@ -820,7 +851,7 @@ TEST_P(CordTest, GetAppendBufferOnTree) {
}
}
TEST_P(CordTest, GetAppendBufferOnTreeWithoutMinCapacity) {
TEST_P(CordAppendBufferTest, GetAppendBufferOnTreeWithoutMinCapacity) {
absl::Cord cord;
for (int i = 0; i < 2; ++i) {
absl::CordBuffer buffer = absl::CordBuffer::CreateWithDefaultLimit(500);
@ -828,13 +859,13 @@ TEST_P(CordTest, GetAppendBufferOnTreeWithoutMinCapacity) {
memcpy(buffer.data(), i ? "def" : "Abc", 3);
cord.Append(std::move(buffer));
}
absl::CordBuffer buffer = cord.GetAppendBuffer(1000, 900);
absl::CordBuffer buffer = GetAppendBuffer(cord, 1000, 900);
EXPECT_GE(buffer.capacity(), 1000);
EXPECT_EQ(buffer.length(), 0);
EXPECT_EQ(cord, "Abcdef");
}
TEST_P(CordTest, GetAppendBufferOnSubstring) {
TEST_P(CordAppendBufferTest, GetAppendBufferOnSubstring) {
// Create a large cord with a single flat and some extra capacity
absl::Cord cord;
absl::CordBuffer buffer = absl::CordBuffer::CreateWithDefaultLimit(500);
@ -844,12 +875,12 @@ TEST_P(CordTest, GetAppendBufferOnSubstring) {
cord.RemovePrefix(1);
// Deny on substring
buffer = cord.GetAppendBuffer(6);
buffer = GetAppendBuffer(cord, 6);
EXPECT_EQ(buffer.length(), 0);
EXPECT_EQ(cord, std::string(449, 'x'));
}
TEST_P(CordTest, GetAppendBufferOnSharedCord) {
TEST_P(CordAppendBufferTest, GetAppendBufferOnSharedCord) {
// Create a shared cord with a single flat and extra capacity
absl::Cord cord;
absl::CordBuffer buffer = absl::CordBuffer::CreateWithDefaultLimit(500);
@ -859,7 +890,7 @@ TEST_P(CordTest, GetAppendBufferOnSharedCord) {
absl::Cord shared_cord = cord;
// Deny on flat
buffer = cord.GetAppendBuffer(6);
buffer = GetAppendBuffer(cord, 6);
EXPECT_EQ(buffer.length(), 0);
EXPECT_EQ(cord, "Abc");
@ -870,7 +901,7 @@ TEST_P(CordTest, GetAppendBufferOnSharedCord) {
shared_cord = cord;
// Deny on tree
buffer = cord.GetAppendBuffer(6);
buffer = GetAppendBuffer(cord, 6);
EXPECT_EQ(buffer.length(), 0);
EXPECT_EQ(cord, "Abcdef");
}

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