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Io.Queue: fix empty and full states being indistinguishable.

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This commit is contained in:
Jacob Young 2025-11-03 21:05:18 -05:00 committed by Jacob Young
parent c603d27f90
commit ea76946d2a
2 changed files with 64 additions and 64 deletions
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107
lib/std/Io.zig
View File

@ -1238,8 +1238,8 @@ pub const TypeErasedQueue = struct {
/// Ring buffer. This data is logically *after* queued getters.
buffer: []u8,
put_index: usize,
get_index: usize,
start: usize,
len: usize,
putters: std.DoublyLinkedList,
getters: std.DoublyLinkedList,
@ -1260,8 +1260,8 @@ pub const TypeErasedQueue = struct {
return .{
.mutex = .init,
.buffer = buffer,
.put_index = 0,
.get_index = 0,
.start = 0,
.len = 0,
.putters = .{},
.getters = .{},
};
@ -1286,6 +1286,16 @@ pub const TypeErasedQueue = struct {
};
}
fn puttableSlice(q: *const TypeErasedQueue) ?[]u8 {
const unwrapped_index = q.start + q.len;
const wrapped_index, const overflow = @subWithOverflow(unwrapped_index, q.buffer.len);
const slice = switch (overflow) {
1 => q.buffer[unwrapped_index..],
0 => q.buffer[wrapped_index..q.start],
};
return if (slice.len > 0) slice else null;
}
fn putLocked(q: *TypeErasedQueue, io: Io, elements: []const u8, min: usize, uncancelable: bool) Cancelable!usize {
// Getters have first priority on the data, and only when the getters
// queue is empty do we start populating the buffer.
@ -1306,20 +1316,12 @@ pub const TypeErasedQueue = struct {
return elements.len;
}
{
const available = q.buffer[q.put_index..];
const copy_len = @min(available.len, remaining.len);
@memcpy(available[0..copy_len], remaining[0..copy_len]);
while (q.puttableSlice()) |slice| {
const copy_len = @min(slice.len, remaining.len);
assert(copy_len > 0);
@memcpy(slice[0..copy_len], remaining[0..copy_len]);
q.len += copy_len;
remaining = remaining[copy_len..];
q.put_index += copy_len;
if (remaining.len == 0) return elements.len;
}
{
const available = q.buffer[0..q.get_index];
const copy_len = @min(available.len, remaining.len);
@memcpy(available[0..copy_len], remaining[0..copy_len]);
remaining = remaining[copy_len..];
q.put_index = copy_len;
if (remaining.len == 0) return elements.len;
}
@ -1354,46 +1356,32 @@ pub const TypeErasedQueue = struct {
};
}
fn gettableSlice(q: *const TypeErasedQueue) ?[]const u8 {
const overlong_slice = q.buffer[q.start..];
const slice = overlong_slice[0..@min(overlong_slice.len, q.len)];
return if (slice.len > 0) slice else null;
}
fn getLocked(q: *@This(), io: Io, buffer: []u8, min: usize, uncancelable: bool) Cancelable!usize {
// The ring buffer gets first priority, then data should come from any
// queued putters, then finally the ring buffer should be filled with
// data from putters so they can be resumed.
var remaining = buffer;
if (q.get_index <= q.put_index) {
const available = q.buffer[q.get_index..q.put_index];
const copy_len = @min(available.len, remaining.len);
@memcpy(remaining[0..copy_len], available[0..copy_len]);
q.get_index += copy_len;
while (q.gettableSlice()) |slice| {
const copy_len = @min(slice.len, remaining.len);
assert(copy_len > 0);
@memcpy(remaining[0..copy_len], slice[0..copy_len]);
q.start += copy_len;
if (q.buffer.len - q.start == 0) q.start = 0;
q.len -= copy_len;
remaining = remaining[copy_len..];
if (remaining.len == 0) {
q.fillRingBufferFromPutters(io);
return buffer.len;
}
} else {
{
const available = q.buffer[q.get_index..];
const copy_len = @min(available.len, remaining.len);
@memcpy(remaining[0..copy_len], available[0..copy_len]);
q.get_index += copy_len;
remaining = remaining[copy_len..];
if (remaining.len == 0) {
q.fillRingBufferFromPutters(io);
return buffer.len;
}
}
{
const available = q.buffer[0..q.put_index];
const copy_len = @min(available.len, remaining.len);
@memcpy(remaining[0..copy_len], available[0..copy_len]);
q.get_index = copy_len;
remaining = remaining[copy_len..];
if (remaining.len == 0) {
q.fillRingBufferFromPutters(io);
return buffer.len;
}
}
}
// Copy directly from putters into buffer.
while (q.putters.popFirst()) |putter_node| {
const putter: *Put = @alignCast(@fieldParentPtr("node", putter_node));
@ -1410,6 +1398,7 @@ pub const TypeErasedQueue = struct {
q.fillRingBufferFromPutters(io);
return buffer.len;
}
// Both ring buffer and putters queue is empty.
const total_filled = buffer.len - remaining.len;
if (total_filled >= min) return total_filled;
@ -1432,30 +1421,20 @@ pub const TypeErasedQueue = struct {
fn fillRingBufferFromPutters(q: *TypeErasedQueue, io: Io) void {
while (q.putters.popFirst()) |putter_node| {
const putter: *Put = @alignCast(@fieldParentPtr("node", putter_node));
{
const available = q.buffer[q.put_index..];
const copy_len = @min(available.len, putter.remaining.len);
@memcpy(available[0..copy_len], putter.remaining[0..copy_len]);
while (q.puttableSlice()) |slice| {
const copy_len = @min(slice.len, putter.remaining.len);
assert(copy_len > 0);
@memcpy(slice[0..copy_len], putter.remaining[0..copy_len]);
q.len += copy_len;
putter.remaining = putter.remaining[copy_len..];
q.put_index += copy_len;
if (putter.remaining.len == 0) {
putter.condition.signal(io);
continue;
break;
}
} else {
q.putters.prepend(putter_node);
break;
}
{
const available = q.buffer[0..q.get_index];
const copy_len = @min(available.len, putter.remaining.len);
@memcpy(available[0..copy_len], putter.remaining[0..copy_len]);
putter.remaining = putter.remaining[copy_len..];
q.put_index = copy_len;
if (putter.remaining.len == 0) {
putter.condition.signal(io);
continue;
}
}
q.putters.prepend(putter_node);
break;
}
}
};

21
lib/std/Io/test.zig
View File

@ -208,3 +208,24 @@ test "select" {
},
}
}
fn testQueue(comptime len: usize) !void {
const io = testing.io;
var buf: [len]usize = undefined;
var queue: Io.Queue(usize) = .init(&buf);
var begin: usize = 0;
for (1..len + 1) |n| {
const end = begin + n;
for (begin..end) |i| try queue.putOne(io, i);
for (begin..end) |i| try expect(try queue.getOne(io) == i);
begin = end;
}
}
test "Queue" {
try testQueue(1);
try testQueue(2);
try testQueue(3);
try testQueue(4);
try testQueue(5);
}