Commit b19d0fb0fd3e4ff023968e77f01848ffb9dce360 | zig

author	Lucas Santos <lucascarvalhosantos91@gmail.com> 2024-09-23 21:20:27-03:00
committer	GitHub <noreply@github.com> 2024-09-23 17:20:27-07:00
log	b19d0fb0fd3e4ff023968e77f01848ffb9dce360
tree	3b591d1f39f59a13377c6a17d5b9a891fd8b0add
parent	d1901c744c9bf2862f99be837325e0a50365c38b
signature	Signed by PGP key B5690EEEBB952194

Improve efficiency of buffered_reader. (#21256)

The previous implementation of buffered_reader always reads from the
unbuffered reader into the internal buffer, and then dumps the data onto
the destination. This is inefficient, as sometimes it's possible to read
directly into the destination. The previous strategy generates more
memory copies and unbuffered reads than necessary.

1 files changed, 39 insertions(+), 33 deletions(-)

lib
- std
  - io
    buffered_reader.zig

lib/std/io/buffered_reader.zig+39-33

...	@@ -17,26 +17,27 @@ pub fn BufferedReader(comptime buffer_size: usize, comptime ReaderType: type) ty	...	@@ -17,26 +17,27 @@ pub fn BufferedReader(comptime buffer_size: usize, comptime ReaderType: type) ty
17	const Self = @This();	17	const Self = @This();
18		18
19	pub fn read(self: *Self, dest: []u8) Error!usize {	19	pub fn read(self: *Self, dest: []u8) Error!usize {
20	var dest_index: usize = 0;	20	// First try reading from the already buffered data onto the destination.
21		21	const current = self.buf[self.start..self.end];
22	while (dest_index < dest.len) {	22	if (current.len != 0) {
23	const written = @min(dest.len - dest_index, self.end - self.start);	23	const to_transfer = @min(current.len, dest.len);
24	@memcpy(dest[dest_index..][0..written], self.buf[self.start..][0..written]);	24	@memcpy(dest[0..to_transfer], current[0..to_transfer]);
25	if (written == 0) {	25	self.start += to_transfer;
26	// buf empty, fill it	26	return to_transfer;
27	const n = try self.unbuffered_reader.read(self.buf[0..]);
28	if (n == 0) {
29	// reading from the unbuffered stream returned nothing
30	// so we have nothing left to read.
31	return dest_index;
32	}
33	self.start = 0;
34	self.end = n;
35	}
36	self.start += written;
37	dest_index += written;
38	}	27	}
39	return dest.len;	28
		29	// If dest is large, read from the unbuffered reader directly into the destination.
		30	if (dest.len >= buffer_size) {
		31	return self.unbuffered_reader.read(dest);
		32	}
		33
		34	// If dest is small, read from the unbuffered reader into our own internal buffer,
		35	// and then transfer to destination.
		36	self.end = try self.unbuffered_reader.read(&self.buf);
		37	const to_transfer = @min(self.end, dest.len);
		38	@memcpy(dest[0..to_transfer], self.buf[0..to_transfer]);
		39	self.start = to_transfer;
		40	return to_transfer;
40	}	41	}
41		42
42	pub fn reader(self: *Self) Reader {	43	pub fn reader(self: *Self) Reader {
...	@@ -134,12 +135,13 @@ test "Block" {	...	@@ -134,12 +135,13 @@ test "Block" {
134	var test_buf_reader: BufferedReader(4, BlockReader) = .{	135	var test_buf_reader: BufferedReader(4, BlockReader) = .{
135	.unbuffered_reader = BlockReader.init(block, 2),	136	.unbuffered_reader = BlockReader.init(block, 2),
136	};	137	};
		138	const reader = test_buf_reader.reader();
137	var out_buf: [4]u8 = undefined;	139	var out_buf: [4]u8 = undefined;
138	_ = try test_buf_reader.read(&out_buf);	140	_ = try reader.readAll(&out_buf);
139	try testing.expectEqualSlices(u8, &out_buf, block);	141	try testing.expectEqualSlices(u8, &out_buf, block);
140	_ = try test_buf_reader.read(&out_buf);	142	_ = try reader.readAll(&out_buf);
141	try testing.expectEqualSlices(u8, &out_buf, block);	143	try testing.expectEqualSlices(u8, &out_buf, block);
142	try testing.expectEqual(try test_buf_reader.read(&out_buf), 0);	144	try testing.expectEqual(try reader.readAll(&out_buf), 0);
143	}	145	}
144		146
145	// len out < block	147	// len out < block
...	@@ -147,14 +149,15 @@ test "Block" {	...	@@ -147,14 +149,15 @@ test "Block" {
147	var test_buf_reader: BufferedReader(4, BlockReader) = .{	149	var test_buf_reader: BufferedReader(4, BlockReader) = .{
148	.unbuffered_reader = BlockReader.init(block, 2),	150	.unbuffered_reader = BlockReader.init(block, 2),
149	};	151	};
		152	const reader = test_buf_reader.reader();
150	var out_buf: [3]u8 = undefined;	153	var out_buf: [3]u8 = undefined;
151	_ = try test_buf_reader.read(&out_buf);	154	_ = try reader.readAll(&out_buf);
152	try testing.expectEqualSlices(u8, &out_buf, "012");	155	try testing.expectEqualSlices(u8, &out_buf, "012");
153	_ = try test_buf_reader.read(&out_buf);	156	_ = try reader.readAll(&out_buf);
154	try testing.expectEqualSlices(u8, &out_buf, "301");	157	try testing.expectEqualSlices(u8, &out_buf, "301");
155	const n = try test_buf_reader.read(&out_buf);	158	const n = try reader.readAll(&out_buf);
156	try testing.expectEqualSlices(u8, out_buf[0..n], "23");	159	try testing.expectEqualSlices(u8, out_buf[0..n], "23");
157	try testing.expectEqual(try test_buf_reader.read(&out_buf), 0);	160	try testing.expectEqual(try reader.readAll(&out_buf), 0);
158	}	161	}
159		162
160	// len out > block	163	// len out > block
...	@@ -162,12 +165,13 @@ test "Block" {	...	@@ -162,12 +165,13 @@ test "Block" {
162	var test_buf_reader: BufferedReader(4, BlockReader) = .{	165	var test_buf_reader: BufferedReader(4, BlockReader) = .{
163	.unbuffered_reader = BlockReader.init(block, 2),	166	.unbuffered_reader = BlockReader.init(block, 2),
164	};	167	};
		168	const reader = test_buf_reader.reader();
165	var out_buf: [5]u8 = undefined;	169	var out_buf: [5]u8 = undefined;
166	_ = try test_buf_reader.read(&out_buf);	170	_ = try reader.readAll(&out_buf);
167	try testing.expectEqualSlices(u8, &out_buf, "01230");	171	try testing.expectEqualSlices(u8, &out_buf, "01230");
168	const n = try test_buf_reader.read(&out_buf);	172	const n = try reader.readAll(&out_buf);
169	try testing.expectEqualSlices(u8, out_buf[0..n], "123");	173	try testing.expectEqualSlices(u8, out_buf[0..n], "123");
170	try testing.expectEqual(try test_buf_reader.read(&out_buf), 0);	174	try testing.expectEqual(try reader.readAll(&out_buf), 0);
171	}	175	}
172		176
173	// len out == 0	177	// len out == 0
...	@@ -175,8 +179,9 @@ test "Block" {	...	@@ -175,8 +179,9 @@ test "Block" {
175	var test_buf_reader: BufferedReader(4, BlockReader) = .{	179	var test_buf_reader: BufferedReader(4, BlockReader) = .{
176	.unbuffered_reader = BlockReader.init(block, 2),	180	.unbuffered_reader = BlockReader.init(block, 2),
177	};	181	};
		182	const reader = test_buf_reader.reader();
178	var out_buf: [0]u8 = undefined;	183	var out_buf: [0]u8 = undefined;
179	_ = try test_buf_reader.read(&out_buf);	184	_ = try reader.readAll(&out_buf);
180	try testing.expectEqualSlices(u8, &out_buf, "");	185	try testing.expectEqualSlices(u8, &out_buf, "");
181	}	186	}
182		187
...	@@ -185,11 +190,12 @@ test "Block" {	...	@@ -185,11 +190,12 @@ test "Block" {
185	var test_buf_reader: BufferedReader(5, BlockReader) = .{	190	var test_buf_reader: BufferedReader(5, BlockReader) = .{
186	.unbuffered_reader = BlockReader.init(block, 2),	191	.unbuffered_reader = BlockReader.init(block, 2),
187	};	192	};
		193	const reader = test_buf_reader.reader();
188	var out_buf: [4]u8 = undefined;	194	var out_buf: [4]u8 = undefined;
189	_ = try test_buf_reader.read(&out_buf);	195	_ = try reader.readAll(&out_buf);
190	try testing.expectEqualSlices(u8, &out_buf, block);	196	try testing.expectEqualSlices(u8, &out_buf, block);
191	_ = try test_buf_reader.read(&out_buf);	197	_ = try reader.readAll(&out_buf);
192	try testing.expectEqualSlices(u8, &out_buf, block);	198	try testing.expectEqualSlices(u8, &out_buf, block);
193	try testing.expectEqual(try test_buf_reader.read(&out_buf), 0);	199	try testing.expectEqual(try reader.readAll(&out_buf), 0);
194	}	200	}
195	}	201	}