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Collect the writes of the adapter sink and pass them on in blocks

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to_cbor(j, o) and its siblings with a std::string, a std::vector or a
std::ostream go through output_adapter_sink, where every write is a virtual
call, and for a stream a call with a sentry on top. That costs more than
encoding the few bytes of most values, which is why those overloads were 1.8
to 3 times slower than the vector-returning ones.

The sink now keeps a 1 KiB buffer and passes it on when it is full, when a
write is larger than the space left (a payload of a KiB or more goes
directly), or when binary_writer::flush() is called at the end of the to_*
function. Everything reaches the adapter in the same order. The destructor
flushes what is left, so a value that throws (invalid UTF-8 with the strict
handler) leaves the same partial output as before; only flush() can report an
error of the adapter, as a destructor must not throw.

Instructions per call (Linux, GCC 13, thousands), to_*(j, std::string&): twitter cbor 4952 -> 3356, twitter ubjson 6762 -> 4647, twitter bson 5518 -> 4704, citm_catalog cbor 10404 -> 7090; to_*(j, std::ostream&): twitter cbor 9178 -> 3844, twitter ubjson 11974 -> 5129, citm_catalog cbor 18374 -> 7554.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>
This commit is contained in:
Niels Lohmann committed 2026-10-22 09:28:46 +02:00
1 parent ef2fee20d8
commit e82ee7375a
4 files changed
+308 -50
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include/nlohmann/json.hpp
+36 -12
View File
@@ -6331,7 +6331,9 @@ public:
static void to_cbor(const basic_json& j, detail::output_adapter<std::uint8_t> o,
const error_handler_t error_handler = detail::binary_writer_default_error_handler())
{
binary_writer<std::uint8_t>(o, error_handler).write_cbor(j);
binary_writer<std::uint8_t> writer(o, error_handler);
writer.write_cbor(j);
writer.flush();
}
/// @brief create a CBOR serialization of a given JSON value
@@ -6339,7 +6341,9 @@ public:
static void to_cbor(const basic_json& j, detail::output_adapter<char> o,
const error_handler_t error_handler = detail::binary_writer_default_error_handler())
{
binary_writer<char>(o, error_handler).write_cbor(j);
binary_writer<char> writer(o, error_handler);
writer.write_cbor(j);
writer.flush();
}
/// @brief create a MessagePack serialization of a given JSON value
@@ -6358,7 +6362,9 @@ public:
static void to_msgpack(const basic_json& j, detail::output_adapter<std::uint8_t> o,
const error_handler_t error_handler = error_handler_t::keep)
{
binary_writer<std::uint8_t>(o, error_handler).write_msgpack(j);
binary_writer<std::uint8_t> writer(o, error_handler);
writer.write_msgpack(j);
writer.flush();
}
/// @brief create a MessagePack serialization of a given JSON value
@@ -6366,7 +6372,9 @@ public:
static void to_msgpack(const basic_json& j, detail::output_adapter<char> o,
const error_handler_t error_handler = error_handler_t::keep)
{
binary_writer<char>(o, error_handler).write_msgpack(j);
binary_writer<char> writer(o, error_handler);
writer.write_msgpack(j);
writer.flush();
}
/// @brief create a UBJSON serialization of a given JSON value
@@ -6388,7 +6396,9 @@ public:
const bool use_size = false, const bool use_type = false,
const error_handler_t error_handler = detail::binary_writer_default_error_handler())
{
binary_writer<std::uint8_t>(o, error_handler).write_ubjson(j, use_size, use_type);
binary_writer<std::uint8_t> writer(o, error_handler);
writer.write_ubjson(j, use_size, use_type);
writer.flush();
}
/// @brief create a UBJSON serialization of a given JSON value
@@ -6397,7 +6407,9 @@ public:
const bool use_size = false, const bool use_type = false,
const error_handler_t error_handler = detail::binary_writer_default_error_handler())
{
binary_writer<char>(o, error_handler).write_ubjson(j, use_size, use_type);
binary_writer<char> writer(o, error_handler);
writer.write_ubjson(j, use_size, use_type);
writer.flush();
}
/// @brief create a BJData serialization of a given JSON value
@@ -6421,7 +6433,9 @@ public:
const bjdata_version_t version = bjdata_version_t::draft2,
const error_handler_t error_handler = detail::binary_writer_default_error_handler())
{
binary_writer<std::uint8_t>(o, error_handler).write_ubjson(j, use_size, use_type, true, true, version);
binary_writer<std::uint8_t> writer(o, error_handler);
writer.write_ubjson(j, use_size, use_type, true, true, version);
writer.flush();
}
/// @brief create a BJData serialization of a given JSON value
@@ -6431,7 +6445,9 @@ public:
const bjdata_version_t version = bjdata_version_t::draft2,
const error_handler_t error_handler = detail::binary_writer_default_error_handler())
{
binary_writer<char>(o, error_handler).write_ubjson(j, use_size, use_type, true, true, version);
binary_writer<char> writer(o, error_handler);
writer.write_ubjson(j, use_size, use_type, true, true, version);
writer.flush();
}
/// @brief create a BSON serialization of a given JSON value
@@ -6450,7 +6466,9 @@ public:
static void to_bson(const basic_json& j, detail::output_adapter<std::uint8_t> o,
const error_handler_t error_handler = detail::binary_writer_default_error_handler())
{
binary_writer<std::uint8_t>(o, error_handler).write_bson(j);
binary_writer<std::uint8_t> writer(o, error_handler);
writer.write_bson(j);
writer.flush();
}
/// @brief create a BSON serialization of a given JSON value
@@ -6458,7 +6476,9 @@ public:
static void to_bson(const basic_json& j, detail::output_adapter<char> o,
const error_handler_t error_handler = detail::binary_writer_default_error_handler())
{
binary_writer<char>(o, error_handler).write_bson(j);
binary_writer<char> writer(o, error_handler);
writer.write_bson(j);
writer.flush();
}
/// @brief create a BON8 serialization of a given JSON value
@@ -6475,14 +6495,18 @@ public:
/// @sa https://json.nlohmann.me/api/basic_json/to_bon8/
static void to_bon8(const basic_json& j, detail::output_adapter<std::uint8_t> o)
{
binary_writer<std::uint8_t>(o).write_bon8(j);
binary_writer<std::uint8_t> writer(o);
writer.write_bon8(j);
writer.flush();
}
/// @brief create a BON8 serialization of a given JSON value
/// @sa https://json.nlohmann.me/api/basic_json/to_bon8/
static void to_bon8(const basic_json& j, detail::output_adapter<char> o)
{
binary_writer<char>(o).write_bon8(j);
binary_writer<char> writer(o);
writer.write_bon8(j);
writer.flush();
}
/// @brief create a JSON value from an input in CBOR format