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io: Correctly align async closure contexts

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This fixes package fetching on Windows.

Previously, `Async/GroupClosure` allocations were only aligned for the
closure struct type, which resulted in panics when `context_alignment`
(or `result_alignment` for that matter) had a greater alignment.
This commit is contained in:
Carl Åstholm 2025-11-05 01:00:44 +01:00
parent 5f1392247d
commit cca2d09950
2 changed files with 166 additions and 84 deletions
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191
lib/std/Io/Threaded.zig
View File

@ -389,6 +389,7 @@ const AsyncClosure = struct {
select_condition: ?*ResetEvent,
context_alignment: std.mem.Alignment,
result_offset: usize,
alloc_len: usize,
const done_reset_event: *ResetEvent = @ptrFromInt(@alignOf(ResetEvent));
@ -425,18 +426,59 @@ const AsyncClosure = struct {
fn contextPointer(ac: *AsyncClosure) [*]u8 {
const base: [*]u8 = @ptrCast(ac);
return base + ac.context_alignment.forward(@sizeOf(AsyncClosure));
const context_offset = ac.context_alignment.forward(@intFromPtr(ac) + @sizeOf(AsyncClosure)) - @intFromPtr(ac);
return base + context_offset;
}
fn waitAndFree(ac: *AsyncClosure, gpa: Allocator, result: []u8) void {
fn init(
gpa: Allocator,
mode: enum { async, concurrent },
result_len: usize,
result_alignment: std.mem.Alignment,
context: []const u8,
context_alignment: std.mem.Alignment,
func: *const fn (context: *const anyopaque, result: *anyopaque) void,
) Allocator.Error!*AsyncClosure {
const max_context_misalignment = context_alignment.toByteUnits() -| @alignOf(AsyncClosure);
const worst_case_context_offset = context_alignment.forward(@sizeOf(AsyncClosure) + max_context_misalignment);
const worst_case_result_offset = result_alignment.forward(worst_case_context_offset + context.len);
const alloc_len = worst_case_result_offset + result_len;
const ac: *AsyncClosure = @ptrCast(@alignCast(try gpa.alignedAlloc(u8, .of(AsyncClosure), alloc_len)));
errdefer comptime unreachable;
const actual_context_addr = context_alignment.forward(@intFromPtr(ac) + @sizeOf(AsyncClosure));
const actual_result_addr = result_alignment.forward(actual_context_addr + context.len);
const actual_result_offset = actual_result_addr - @intFromPtr(ac);
ac.* = .{
.closure = .{
.cancel_tid = .none,
.start = start,
.is_concurrent = switch (mode) {
.async => false,
.concurrent => true,
},
},
.func = func,
.context_alignment = context_alignment,
.result_offset = actual_result_offset,
.alloc_len = alloc_len,
.reset_event = .unset,
.select_condition = null,
};
@memcpy(ac.contextPointer()[0..context.len], context);
return ac;
}
fn waitAndDeinit(ac: *AsyncClosure, gpa: Allocator, result: []u8) void {
ac.reset_event.waitUncancelable();
@memcpy(result, ac.resultPointer()[0..result.len]);
free(ac, gpa, result.len);
ac.deinit(gpa);
}
fn free(ac: *AsyncClosure, gpa: Allocator, result_len: usize) void {
fn deinit(ac: *AsyncClosure, gpa: Allocator) void {
const base: [*]align(@alignOf(AsyncClosure)) u8 = @ptrCast(ac);
gpa.free(base[0 .. ac.result_offset + result_len]);
gpa.free(base[0..ac.alloc_len]);
}
};
@ -452,6 +494,7 @@ fn async(
start(context.ptr, result.ptr);
return null;
}
const t: *Threaded = @ptrCast(@alignCast(userdata));
const cpu_count = t.cpu_count catch {
return concurrent(userdata, result.len, result_alignment, context, context_alignment, start) catch {
@ -459,37 +502,20 @@ fn async(
return null;
};
};
const gpa = t.allocator;
const context_offset = context_alignment.forward(@sizeOf(AsyncClosure));
const result_offset = result_alignment.forward(context_offset + context.len);
const n = result_offset + result.len;
const ac: *AsyncClosure = @ptrCast(@alignCast(gpa.alignedAlloc(u8, .of(AsyncClosure), n) catch {
const ac = AsyncClosure.init(gpa, .async, result.len, result_alignment, context, context_alignment, start) catch {
start(context.ptr, result.ptr);
return null;
}));
ac.* = .{
.closure = .{
.cancel_tid = .none,
.start = AsyncClosure.start,
.is_concurrent = false,
},
.func = start,
.context_alignment = context_alignment,
.result_offset = result_offset,
.reset_event = .unset,
.select_condition = null,
};
@memcpy(ac.contextPointer()[0..context.len], context);
t.mutex.lock();
const thread_capacity = cpu_count - 1 + t.concurrent_count;
t.threads.ensureTotalCapacityPrecise(gpa, thread_capacity) catch {
t.mutex.unlock();
ac.free(gpa, result.len);
ac.deinit(gpa);
start(context.ptr, result.ptr);
return null;
};
@ -501,7 +527,7 @@ fn async(
if (t.threads.items.len == 0) {
assert(t.run_queue.popFirst() == &ac.closure.node);
t.mutex.unlock();
ac.free(gpa, result.len);
ac.deinit(gpa);
start(context.ptr, result.ptr);
return null;
}
@ -530,27 +556,11 @@ fn concurrent(
const t: *Threaded = @ptrCast(@alignCast(userdata));
const cpu_count = t.cpu_count catch 1;
const gpa = t.allocator;
const context_offset = context_alignment.forward(@sizeOf(AsyncClosure));
const result_offset = result_alignment.forward(context_offset + context.len);
const n = result_offset + result_len;
const ac_bytes = gpa.alignedAlloc(u8, .of(AsyncClosure), n) catch
return error.ConcurrencyUnavailable;
const ac: *AsyncClosure = @ptrCast(@alignCast(ac_bytes));
ac.* = .{
.closure = .{
.cancel_tid = .none,
.start = AsyncClosure.start,
.is_concurrent = true,
},
.func = start,
.context_alignment = context_alignment,
.result_offset = result_offset,
.reset_event = .unset,
.select_condition = null,
const gpa = t.allocator;
const ac = AsyncClosure.init(gpa, .concurrent, result_len, result_alignment, context, context_alignment, start) catch {
return error.ConcurrencyUnavailable;
};
@memcpy(ac.contextPointer()[0..context.len], context);
t.mutex.lock();
@ -559,7 +569,7 @@ fn concurrent(
t.threads.ensureTotalCapacity(gpa, thread_capacity) catch {
t.mutex.unlock();
ac.free(gpa, result_len);
ac.deinit(gpa);
return error.ConcurrencyUnavailable;
};
@ -569,7 +579,7 @@ fn concurrent(
const thread = std.Thread.spawn(.{ .stack_size = t.stack_size }, worker, .{t}) catch {
assert(t.run_queue.popFirst() == &ac.closure.node);
t.mutex.unlock();
ac.free(gpa, result_len);
ac.deinit(gpa);
return error.ConcurrencyUnavailable;
};
t.threads.appendAssumeCapacity(thread);
@ -588,7 +598,7 @@ const GroupClosure = struct {
node: std.SinglyLinkedList.Node,
func: *const fn (*Io.Group, context: *anyopaque) void,
context_alignment: std.mem.Alignment,
context_len: usize,
alloc_len: usize,
fn start(closure: *Closure) void {
const gc: *GroupClosure = @alignCast(@fieldParentPtr("closure", closure));
@ -616,22 +626,48 @@ const GroupClosure = struct {
if (prev_state == (sync_one_pending | sync_is_waiting)) reset_event.set();
}
fn free(gc: *GroupClosure, gpa: Allocator) void {
const base: [*]align(@alignOf(GroupClosure)) u8 = @ptrCast(gc);
gpa.free(base[0..contextEnd(gc.context_alignment, gc.context_len)]);
}
fn contextOffset(context_alignment: std.mem.Alignment) usize {
return context_alignment.forward(@sizeOf(GroupClosure));
}
fn contextEnd(context_alignment: std.mem.Alignment, context_len: usize) usize {
return contextOffset(context_alignment) + context_len;
}
fn contextPointer(gc: *GroupClosure) [*]u8 {
const base: [*]u8 = @ptrCast(gc);
return base + contextOffset(gc.context_alignment);
const context_offset = gc.context_alignment.forward(@intFromPtr(gc) + @sizeOf(GroupClosure)) - @intFromPtr(gc);
return base + context_offset;
}
/// Does not initialize the `node` field.
fn init(
gpa: Allocator,
t: *Threaded,
group: *Io.Group,
context: []const u8,
context_alignment: std.mem.Alignment,
func: *const fn (*Io.Group, context: *const anyopaque) void,
) Allocator.Error!*GroupClosure {
const max_context_misalignment = context_alignment.toByteUnits() -| @alignOf(GroupClosure);
const worst_case_context_offset = context_alignment.forward(@sizeOf(GroupClosure) + max_context_misalignment);
const alloc_len = worst_case_context_offset + context.len;
const gc: *GroupClosure = @ptrCast(@alignCast(try gpa.alignedAlloc(u8, .of(GroupClosure), alloc_len)));
errdefer comptime unreachable;
gc.* = .{
.closure = .{
.cancel_tid = .none,
.start = start,
.is_concurrent = false,
},
.t = t,
.group = group,
.node = undefined,
.func = func,
.context_alignment = context_alignment,
.alloc_len = alloc_len,
};
@memcpy(gc.contextPointer()[0..context.len], context);
return gc;
}
fn deinit(gc: *GroupClosure, gpa: Allocator) void {
const base: [*]align(@alignOf(GroupClosure)) u8 = @ptrCast(gc);
gpa.free(base[0..gc.alloc_len]);
}
const sync_is_waiting: usize = 1 << 0;
@ -646,27 +682,14 @@ fn groupAsync(
start: *const fn (*Io.Group, context: *const anyopaque) void,
) void {
if (builtin.single_threaded) return start(group, context.ptr);
const t: *Threaded = @ptrCast(@alignCast(userdata));
const cpu_count = t.cpu_count catch 1;
const gpa = t.allocator;
const n = GroupClosure.contextEnd(context_alignment, context.len);
const gc: *GroupClosure = @ptrCast(@alignCast(gpa.alignedAlloc(u8, .of(GroupClosure), n) catch {
const gc = GroupClosure.init(gpa, t, group, context, context_alignment, start) catch {
return start(group, context.ptr);
}));
gc.* = .{
.closure = .{
.cancel_tid = .none,
.start = GroupClosure.start,
.is_concurrent = false,
},
.t = t,
.group = group,
.node = undefined,
.func = start,
.context_alignment = context_alignment,
.context_len = context.len,
};
@memcpy(gc.contextPointer()[0..context.len], context);
t.mutex.lock();
@ -678,7 +701,7 @@ fn groupAsync(
t.threads.ensureTotalCapacityPrecise(gpa, thread_capacity) catch {
t.mutex.unlock();
gc.free(gpa);
gc.deinit(gpa);
return start(group, context.ptr);
};
@ -688,7 +711,7 @@ fn groupAsync(
const thread = std.Thread.spawn(.{ .stack_size = t.stack_size }, worker, .{t}) catch {
assert(t.run_queue.popFirst() == &gc.closure.node);
t.mutex.unlock();
gc.free(gpa);
gc.deinit(gpa);
return start(group, context.ptr);
};
t.threads.appendAssumeCapacity(thread);
@ -730,7 +753,7 @@ fn groupWait(userdata: ?*anyopaque, group: *Io.Group, token: *anyopaque) void {
while (true) {
const gc: *GroupClosure = @fieldParentPtr("node", node);
const node_next = node.next;
gc.free(gpa);
gc.deinit(gpa);
node = node_next orelse break;
}
}
@ -761,7 +784,7 @@ fn groupCancel(userdata: ?*anyopaque, group: *Io.Group, token: *anyopaque) void
while (true) {
const gc: *GroupClosure = @fieldParentPtr("node", node);
const node_next = node.next;
gc.free(gpa);
gc.deinit(gpa);
node = node_next orelse break;
}
}
@ -776,7 +799,7 @@ fn await(
_ = result_alignment;
const t: *Threaded = @ptrCast(@alignCast(userdata));
const closure: *AsyncClosure = @ptrCast(@alignCast(any_future));
closure.waitAndFree(t.allocator, result);
closure.waitAndDeinit(t.allocator, result);
}
fn cancel(
@ -789,7 +812,7 @@ fn cancel(
const t: *Threaded = @ptrCast(@alignCast(userdata));
const ac: *AsyncClosure = @ptrCast(@alignCast(any_future));
ac.closure.requestCancel();
ac.waitAndFree(t.allocator, result);
ac.waitAndDeinit(t.allocator, result);
}
fn cancelRequested(userdata: ?*anyopaque) bool {

59
lib/std/Io/Threaded/test.zig
View File

@ -56,3 +56,62 @@ test "concurrent vs concurrent prevents deadlock via oversubscription" {
getter.await(io);
putter.await(io);
}
const ByteArray256 = struct { x: [32]u8 align(32) };
const ByteArray512 = struct { x: [64]u8 align(64) };
fn concatByteArrays(a: ByteArray256, b: ByteArray256) ByteArray512 {
return .{ .x = a.x ++ b.x };
}
test "async/concurrent context and result alignment" {
var buffer: [2048]u8 align(@alignOf(ByteArray512)) = undefined;
var fba: std.heap.FixedBufferAllocator = .init(&buffer);
var threaded: std.Io.Threaded = .init(fba.allocator());
defer threaded.deinit();
const io = threaded.io();
const a: ByteArray256 = .{ .x = @splat(2) };
const b: ByteArray256 = .{ .x = @splat(3) };
const expected: ByteArray512 = .{ .x = @as([32]u8, @splat(2)) ++ @as([32]u8, @splat(3)) };
{
var future = io.async(concatByteArrays, .{ a, b });
const result = future.await(io);
try std.testing.expectEqualSlices(u8, &expected.x, &result.x);
}
{
var future = io.concurrent(concatByteArrays, .{ a, b }) catch |err| switch (err) {
error.ConcurrencyUnavailable => {
try testing.expect(builtin.single_threaded);
return;
},
};
const result = future.await(io);
try std.testing.expectEqualSlices(u8, &expected.x, &result.x);
}
}
fn concatByteArraysResultPtr(a: ByteArray256, b: ByteArray256, result: *ByteArray512) void {
result.* = .{ .x = a.x ++ b.x };
}
test "Group.async context alignment" {
var buffer: [2048]u8 align(@alignOf(ByteArray512)) = undefined;
var fba: std.heap.FixedBufferAllocator = .init(&buffer);
var threaded: std.Io.Threaded = .init(fba.allocator());
defer threaded.deinit();
const io = threaded.io();
const a: ByteArray256 = .{ .x = @splat(2) };
const b: ByteArray256 = .{ .x = @splat(3) };
const expected: ByteArray512 = .{ .x = @as([32]u8, @splat(2)) ++ @as([32]u8, @splat(3)) };
var group: std.Io.Group = .init;
var result: ByteArray512 = undefined;
group.async(io, concatByteArraysResultPtr, .{ a, b, &result });
group.wait(io);
try std.testing.expectEqualSlices(u8, &expected.x, &result.x);
}