89 lines
2.5 KiB
Zig
89 lines
2.5 KiB
Zig
const std = @import("std.zig");
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const assert = std.debug.assert;
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const testing = std.testing;
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/// Thread-safe initialization of global data.
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/// TODO use a mutex instead of a spinlock
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pub fn lazyInit(comptime T: type) LazyInit(T) {
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return LazyInit(T){
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.data = undefined,
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};
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}
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fn LazyInit(comptime T: type) type {
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return struct {
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state: State = .NotResolved,
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data: Data,
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const State = enum(u8) {
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NotResolved,
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Resolving,
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Resolved,
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};
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const Self = @This();
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// TODO this isn't working for void, investigate and then remove this special case
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const Data = if (@sizeOf(T) == 0) u8 else T;
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const Ptr = if (T == void) void else *T;
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/// Returns a usable pointer to the initialized data,
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/// or returns null, indicating that the caller should
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/// perform the initialization and then call resolve().
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pub fn get(self: *Self) ?Ptr {
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while (true) {
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var state = @cmpxchgWeak(State, &self.state, .NotResolved, .Resolving, .SeqCst, .SeqCst) orelse return null;
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switch (state) {
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.NotResolved => continue,
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.Resolving => {
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// TODO mutex instead of a spinlock
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continue;
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},
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.Resolved => {
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if (@sizeOf(T) == 0) {
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return @as(T, undefined);
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} else {
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return &self.data;
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}
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},
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else => unreachable,
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}
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}
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}
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pub fn resolve(self: *Self) void {
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const prev = @atomicRmw(State, &self.state, .Xchg, .Resolved, .SeqCst);
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assert(prev != .Resolved); // resolve() called twice
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}
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};
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}
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var global_number = lazyInit(i32);
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test "std.lazyInit" {
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if (global_number.get()) |_| @panic("bad") else {
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global_number.data = 1234;
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global_number.resolve();
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}
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if (global_number.get()) |x| {
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testing.expect(x.* == 1234);
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} else {
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@panic("bad");
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}
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if (global_number.get()) |x| {
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testing.expect(x.* == 1234);
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} else {
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@panic("bad");
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}
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}
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var global_void = lazyInit(void);
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test "std.lazyInit(void)" {
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if (global_void.get()) |_| @panic("bad") else {
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global_void.resolve();
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}
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testing.expect(global_void.get() != null);
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testing.expect(global_void.get() != null);
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}
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