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Default size for IO::Buffer. #5300

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Dec 18, 2021
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1 change: 1 addition & 0 deletions include/ruby/io/buffer.h
Original file line number Diff line number Diff line change
Expand Up @@ -23,6 +23,7 @@ RBIMPL_SYMBOL_EXPORT_BEGIN()

RUBY_EXTERN VALUE rb_cIOBuffer;
RUBY_EXTERN size_t RUBY_IO_BUFFER_PAGE_SIZE;
RUBY_EXTERN size_t RUBY_IO_BUFFER_DEFAULT_SIZE;

enum rb_io_buffer_flags {
// The memory in the buffer is owned by someone else.
Expand Down
42 changes: 38 additions & 4 deletions io_buffer.c
Original file line number Diff line number Diff line change
Expand Up @@ -15,6 +15,7 @@

VALUE rb_cIOBuffer;
size_t RUBY_IO_BUFFER_PAGE_SIZE;
size_t RUBY_IO_BUFFER_DEFAULT_SIZE;

#ifdef _WIN32
#else
Expand Down Expand Up @@ -347,14 +348,20 @@ io_buffer_map(int argc, VALUE *argv, VALUE klass)
VALUE
rb_io_buffer_initialize(int argc, VALUE *argv, VALUE self)
{
if (argc < 1 || argc > 2) {
rb_error_arity(argc, 1, 2);
if (argc < 0 || argc > 2) {
rb_error_arity(argc, 0, 2);
}

struct rb_io_buffer *data = NULL;
TypedData_Get_Struct(self, struct rb_io_buffer, &rb_io_buffer_type, data);

size_t size = RB_NUM2SIZE(argv[0]);
size_t size;

if (argc > 0) {
size = RB_NUM2SIZE(argv[0]);
} else {
size = RUBY_IO_BUFFER_DEFAULT_SIZE;
}

enum rb_io_buffer_flags flags = 0;
if (argc >= 2) {
Expand Down Expand Up @@ -1068,6 +1075,30 @@ io_buffer_clear(int argc, VALUE *argv, VALUE self)
return self;
}

static
size_t io_buffer_default_size(size_t page_size) {
// Platform agnostic default size, based on emperical performance observation:
const size_t platform_agnostic_default_size = 64*1024;

// Allow user to specify custom default buffer size:
const char *default_size = getenv("RUBY_IO_BUFFER_DEFAULT_SIZE");
if (default_size) {
// For the purpose of setting a default size, 2^31 is an acceptable maximum:
int value = atoi(default_size);

// assuming sizeof(int) <= sizeof(size_t)
if (value > 0) {
return value;
}
}

if (platform_agnostic_default_size < page_size) {
return page_size;
}

return platform_agnostic_default_size;
}

void
Init_IO_Buffer(void)
{
Expand All @@ -1084,8 +1115,11 @@ Init_IO_Buffer(void)
RUBY_IO_BUFFER_PAGE_SIZE = sysconf(_SC_PAGESIZE);
#endif

// Efficient sicing of mapped buffers:
RUBY_IO_BUFFER_DEFAULT_SIZE = io_buffer_default_size(RUBY_IO_BUFFER_PAGE_SIZE);

// Efficient sizing of mapped buffers:
rb_define_const(rb_cIOBuffer, "PAGE_SIZE", SIZET2NUM(RUBY_IO_BUFFER_PAGE_SIZE));
rb_define_const(rb_cIOBuffer, "DEFAULT_SIZE", SIZET2NUM(RUBY_IO_BUFFER_DEFAULT_SIZE));

rb_define_singleton_method(rb_cIOBuffer, "map", io_buffer_map, -1);

Expand Down
4 changes: 4 additions & 0 deletions test/ruby/test_io_buffer.rb
Original file line number Diff line number Diff line change
Expand Up @@ -9,6 +9,10 @@ class TestIOBuffer < Test::Unit::TestCase
Warning[:experimental] = experimental
end

def test_default_size
assert_equal IO::Buffer::DEFAULT_SIZE, IO::Buffer.new.size
end

def assert_negative(value)
assert(value < 0, "Expected #{value} to be negative!")
end
Expand Down