Commit 834609038c83e0122b506fadfa38b9acb7ee9068 | zig

author	Luuk de Gram <luuk@degram.dev> 2023-06-21 21:44:53+02:00
committer	Luuk de Gram <luuk@degram.dev> 2023-06-26 20:00:57+02:00
log	834609038c83e0122b506fadfa38b9acb7ee9068
tree	b738876952e39d484ddb642a28ce4763c4771098
parent	10bf58b2db0e340137228f706ee2e8a67b46a892
signature	Commit is signed but in an unrecognized format.

std: implement `join` for WASI-threads

We now reset the Thread ID to 0 and wake up the main thread listening
for the thread to finish. We use inline assembly as we cannot use
the stack to set the thread ID as it could possibly clobber any
of the memory.

Currently, we leak the memory that was allocated for the thread.
We need to implement a way where we can clean up the memory without
using the stack (as the stack is stored inside this same memory).

1 files changed, 59 insertions(+), 8 deletions(-)

lib
- std
  - Thread.zig

lib/std/Thread.zig+59-8

...	@@ -790,7 +790,40 @@ const WasiThreadImpl = struct {	...	@@ -790,7 +790,40 @@ const WasiThreadImpl = struct {
790	}	790	}
791		791
792	fn join(self: Impl) void {	792	fn join(self: Impl) void {
793	_ = self;	793	// TODO cleanup memory
		794	// The memory also contains the thread's stack, which is problematic while freeing the memory
		795	// defer self.thread.allocator.free(self.thread.memory);
		796
		797	var spin: u8 = 10;
		798	while (true) {
		799	const tid = self.thread.tid.load(.SeqCst);
		800	if (tid == 0) {
		801	break;
		802	}
		803
		804	if (spin > 0) {
		805	spin -= 1;
		806	std.atomic.spinLoopHint();
		807	continue;
		808	}
		809
		810	const result = asm (
		811	\\local.get %[ptr]
		812	\\local.get %[expected]
		813	\\i64.const -1 # infinite
		814	\\memory.atomic.wait32 0
		815	\\local.set %[ret]
		816	: [ret] "=r" (-> u32),
		817	: [ptr] "r" (&self.thread.tid.value),
		818	[expected] "r" (tid),
		819	);
		820	switch (result) {
		821	0 => continue, // ok
		822	1 => continue, // expected =! loaded
		823	2 => unreachable, // timeout (infinite)
		824	else => unreachable,
		825	}
		826	}
794	}	827	}
795		828
796	fn spawn(config: std.Thread.SpawnConfig, comptime f: anytype, args: anytype) !WasiThreadImpl {	829	fn spawn(config: std.Thread.SpawnConfig, comptime f: anytype, args: anytype) !WasiThreadImpl {
...	@@ -868,25 +901,43 @@ const WasiThreadImpl = struct {	...	@@ -868,25 +901,43 @@ const WasiThreadImpl = struct {
868	return .{ .thread = &instance.thread };	901	return .{ .thread = &instance.thread };
869	}	902	}
870		903
871	export fn wasi_thread_start(tid: i32, arg: *const Instance) void {	904	/// Bootstrap procedure, called by the HOST environment after thread creation.
		905	export fn wasi_thread_start(tid: i32, arg: *Instance) void {
872	__set_stack_pointer(arg.thread.memory.ptr + arg.stack_pointer);	906	__set_stack_pointer(arg.thread.memory.ptr + arg.stack_pointer);
873	__wasm_init_tls(arg.thread.memory.ptr + arg.tls_base);	907	__wasm_init_tls(arg.thread.memory.ptr + arg.tls_base);
874	WasiThreadImpl.tls_thread_id = @intCast(u32, tid);	908	WasiThreadImpl.tls_thread_id = @intCast(u32, tid);
875		909
876	// finished bootstrapping, call user's procedure.	910	// Finished bootstrapping, call user's procedure.
877	arg.call_back(arg.raw_ptr);	911	arg.call_back(arg.raw_ptr);
		912
		913	// Thread finished. Reset Thread ID and wake up the main thread if needed.
		914	// We use inline assembly here as we must ensure not to use the stack.
		915	asm volatile (
		916	\\ local.get %[ptr]
		917	\\ i32.const 0
		918	\\ i32.atomic.store 0
		919	:
		920	: [ptr] "r" (&arg.thread.tid.value),
		921	);
		922	asm volatile (
		923	\\ local.get %[ptr]
		924	\\ i32.const 1 # waiters
		925	\\ memory.atomic.notify 0
		926	\\ drop # no need to know the waiters
		927	:
		928	: [ptr] "r" (&arg.thread.tid.value),
		929	);
878	}	930	}
879		931
880	// Asks the host to create a new thread for us.	932	/// Asks the host to create a new thread for us.
881	// Newly created thread wil lcall `wasi_tread_start` with the thread ID as well	933	/// Newly created thread will call `wasi_tread_start` with the thread ID as well
882	// as the input `arg` that was provided to `spawnWasiThread`	934	/// as the input `arg` that was provided to `spawnWasiThread`
883	const spawnWasiThread = @"thread-spawn";	935	const spawnWasiThread = @"thread-spawn";
884	extern "wasi" fn @"thread-spawn"(arg: *const Instance) i32;	936	extern "wasi" fn @"thread-spawn"(arg: *Instance) i32;
885		937
886	/// Initializes the TLS data segment starting at `memory`.	938	/// Initializes the TLS data segment starting at `memory`.
887	/// This is a synthetic function, generated by the linker.	939	/// This is a synthetic function, generated by the linker.
888	extern fn __wasm_init_tls(memory: [*]u8) void;	940	extern fn __wasm_init_tls(memory: [*]u8) void;
889	extern fn __set_stack_pointer(ptr: [*]u8) void;
890		941
891	/// Returns a pointer to the base of the TLS data segment for the current thread	942	/// Returns a pointer to the base of the TLS data segment for the current thread
892	inline fn __tls_base() [*]u8 {	943	inline fn __tls_base() [*]u8 {