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std.Progress: fix race condition with setIpcFd

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The update thread was sometimes reading the special state and then
incorrectly getting 0 for the file descriptor, making it hang since it
tried to read from stdin.
This commit is contained in:
Andrew Kelley 2024-05-27 15:22:18 -07:00
parent bb1f4d2bda
commit aca7feb8fa
1 changed files with 19 additions and 7 deletions
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26
lib/std/Progress.zig
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@ -85,6 +85,7 @@ pub const Node = struct {
estimated_total_count: u32,
name: [max_name_len]u8,
/// Not thread-safe.
fn getIpcFd(s: Storage) ?posix.fd_t {
return if (s.estimated_total_count == std.math.maxInt(u32)) switch (@typeInfo(posix.fd_t)) {
.Int => @bitCast(s.completed_count),
@ -93,15 +94,21 @@ pub const Node = struct {
} else null;
}
/// Thread-safe.
fn setIpcFd(s: *Storage, fd: posix.fd_t) void {
s.estimated_total_count = std.math.maxInt(u32);
s.completed_count = switch (@typeInfo(posix.fd_t)) {
const integer: u32 = switch (@typeInfo(posix.fd_t)) {
.Int => @bitCast(fd),
.Pointer => @intFromPtr(fd),
else => @compileError("unsupported fd_t of " ++ @typeName(posix.fd_t)),
};
// `estimated_total_count` max int indicates the special state that
// causes `completed_count` to be treated as a file descriptor, so
// the order here matters.
@atomicStore(u32, &s.completed_count, integer, .seq_cst);
@atomicStore(u32, &s.estimated_total_count, std.math.maxInt(u32), .seq_cst);
}
/// Not thread-safe.
fn byteSwap(s: *Storage) void {
s.completed_count = @byteSwap(s.completed_count);
s.estimated_total_count = @byteSwap(s.estimated_total_count);
@ -208,7 +215,9 @@ pub const Node = struct {
pub fn setEstimatedTotalItems(n: Node, count: usize) void {
const index = n.index.unwrap() orelse return;
const storage = storageByIndex(index);
@atomicStore(u32, &storage.estimated_total_count, std.math.lossyCast(u32, count), .monotonic);
// Avoid u32 max int which is used to indicate a special state.
const saturated = @min(std.math.maxInt(u32) - 1, count);
@atomicStore(u32, &storage.estimated_total_count, saturated, .monotonic);
}
/// Thread-safe.
@ -243,10 +252,13 @@ pub const Node = struct {
}
}
/// Posix-only. Used by `std.process.Child`.
/// Posix-only. Used by `std.process.Child`. Thread-safe.
pub fn setIpcFd(node: Node, fd: posix.fd_t) void {
const index = node.index.unwrap() orelse return;
assert(fd != -1);
assert(fd >= 0);
assert(fd != posix.STDOUT_FILENO);
assert(fd != posix.STDIN_FILENO);
assert(fd != posix.STDERR_FILENO);
storageByIndex(index).setIpcFd(fd);
}
@ -582,8 +594,8 @@ fn serialize(serialized_buffer: *Serialized.Buffer) Serialized {
while (begin_parent != .unused) {
const dest_storage = &serialized_buffer.storage[serialized_len];
@memcpy(&dest_storage.name, &storage_ptr.name);
dest_storage.completed_count = @atomicLoad(u32, &storage_ptr.completed_count, .monotonic);
dest_storage.estimated_total_count = @atomicLoad(u32, &storage_ptr.estimated_total_count, .monotonic);
dest_storage.completed_count = @atomicLoad(u32, &storage_ptr.completed_count, .seq_cst);
dest_storage.estimated_total_count = @atomicLoad(u32, &storage_ptr.estimated_total_count, .seq_cst);
const end_parent = @atomicLoad(Node.Parent, parent_ptr, .seq_cst);
if (begin_parent == end_parent) {
any_ipc = any_ipc or (dest_storage.getIpcFd() != null);