Commit 9b8e23934b
Changed files (18)
doc/langref.html.in
@@ -6714,6 +6714,25 @@ pub fn build(b: *Builder) void {
{#header_close#}
{#see_also|Compile Variables|Zig Build System|Undefined Behavior#}
{#header_close#}
+
+ {#header_open|Single Threaded Builds#}
+ <p>Zig has a compile option <code>--single-threaded</code> which has the following effects:
+ <ul>
+ <li>{#link|@atomicLoad#} is emitted as a normal load.</li>
+ <li>{#link|@atomicRmw#} is emitted as a normal memory load, modify, store.</li>
+ <li>{#link|@fence#} becomes a no-op.</li>
+ <li>Variables which have Thread Local Storage instead become globals. TODO thread local variables
+ are not implemented yet.</li>
+ <li>The overhead of {#link|Coroutines#} becomes equivalent to function call overhead.
+ TODO: please note this will not be implemented until the upcoming Coroutine Rewrite</li>
+ <li>The {#syntax#}@import("builtin").single_threaded{#endsyntax#} becomes {#syntax#}true{#endsyntax#}
+ and therefore various userland APIs which read this variable become more efficient.
+ For example {#syntax#}std.Mutex{#endsyntax#} becomes
+ an empty data structure and all of its functions become no-ops.</li>
+ </ul>
+ </p>
+ {#header_close#}
+
{#header_open|Undefined Behavior#}
<p>
Zig has many instances of undefined behavior. If undefined behavior is
src/all_types.hpp
@@ -1808,6 +1808,7 @@ struct CodeGen {
bool is_static;
bool strip_debug_symbols;
bool is_test_build;
+ bool is_single_threaded;
bool is_native_target;
bool linker_rdynamic;
bool no_rosegment_workaround;
src/codegen.cpp
@@ -118,6 +118,7 @@ CodeGen *codegen_create(Buf *root_src_path, const ZigTarget *target, OutType out
g->string_literals_table.init(16);
g->type_info_cache.init(32);
g->is_test_build = false;
+ g->is_single_threaded = false;
buf_resize(&g->global_asm, 0);
for (size_t i = 0; i < array_length(symbols_that_llvm_depends_on); i += 1) {
@@ -7377,6 +7378,7 @@ Buf *codegen_generate_builtin_source(CodeGen *g) {
buf_appendf(contents, "pub const endian = %s;\n", endian_str);
}
buf_appendf(contents, "pub const is_test = %s;\n", bool_to_str(g->is_test_build));
+ buf_appendf(contents, "pub const single_threaded = %s;\n", bool_to_str(g->is_single_threaded));
buf_appendf(contents, "pub const os = Os.%s;\n", cur_os);
buf_appendf(contents, "pub const arch = Arch.%s;\n", cur_arch);
buf_appendf(contents, "pub const environ = Environ.%s;\n", cur_environ);
@@ -7411,6 +7413,7 @@ static Error define_builtin_compile_vars(CodeGen *g) {
cache_buf(&cache_hash, compiler_id);
cache_int(&cache_hash, g->build_mode);
cache_bool(&cache_hash, g->is_test_build);
+ cache_bool(&cache_hash, g->is_single_threaded);
cache_int(&cache_hash, g->zig_target.arch.arch);
cache_int(&cache_hash, g->zig_target.arch.sub_arch);
cache_int(&cache_hash, g->zig_target.vendor);
@@ -8329,6 +8332,7 @@ static Error check_cache(CodeGen *g, Buf *manifest_dir, Buf *digest) {
cache_bool(ch, g->is_static);
cache_bool(ch, g->strip_debug_symbols);
cache_bool(ch, g->is_test_build);
+ cache_bool(ch, g->is_single_threaded);
cache_bool(ch, g->is_native_target);
cache_bool(ch, g->linker_rdynamic);
cache_bool(ch, g->no_rosegment_workaround);
src/main.cpp
@@ -59,6 +59,7 @@ static int print_full_usage(const char *arg0) {
" --release-fast build with optimizations on and safety off\n"
" --release-safe build with optimizations on and safety on\n"
" --release-small build with size optimizations on and safety off\n"
+ " --single-threaded source may assume it is only used single-threaded\n"
" --static output will be statically linked\n"
" --strip exclude debug symbols\n"
" --target-arch [name] specify target architecture\n"
@@ -393,6 +394,7 @@ int main(int argc, char **argv) {
bool no_rosegment_workaround = false;
bool system_linker_hack = false;
TargetSubsystem subsystem = TargetSubsystemAuto;
+ bool is_single_threaded = false;
if (argc >= 2 && strcmp(argv[1], "build") == 0) {
Buf zig_exe_path_buf = BUF_INIT;
@@ -550,6 +552,8 @@ int main(int argc, char **argv) {
disable_pic = true;
} else if (strcmp(arg, "--system-linker-hack") == 0) {
system_linker_hack = true;
+ } else if (strcmp(arg, "--single-threaded") == 0) {
+ is_single_threaded = true;
} else if (strcmp(arg, "--test-cmd-bin") == 0) {
test_exec_args.append(nullptr);
} else if (arg[1] == 'L' && arg[2] != 0) {
@@ -816,6 +820,7 @@ int main(int argc, char **argv) {
switch (cmd) {
case CmdBuiltin: {
CodeGen *g = codegen_create(nullptr, target, out_type, build_mode, get_zig_lib_dir());
+ g->is_single_threaded = is_single_threaded;
Buf *builtin_source = codegen_generate_builtin_source(g);
if (fwrite(buf_ptr(builtin_source), 1, buf_len(builtin_source), stdout) != buf_len(builtin_source)) {
fprintf(stderr, "unable to write to stdout: %s\n", strerror(ferror(stdout)));
@@ -889,6 +894,7 @@ int main(int argc, char **argv) {
codegen_set_out_name(g, buf_out_name);
codegen_set_lib_version(g, ver_major, ver_minor, ver_patch);
codegen_set_is_test(g, cmd == CmdTest);
+ g->is_single_threaded = is_single_threaded;
codegen_set_linker_script(g, linker_script);
if (each_lib_rpath)
codegen_set_each_lib_rpath(g, each_lib_rpath);
std/atomic/queue.zig
@@ -170,20 +170,36 @@ test "std.atomic.Queue" {
.get_count = 0,
};
- var putters: [put_thread_count]*std.os.Thread = undefined;
- for (putters) |*t| {
- t.* = try std.os.spawnThread(&context, startPuts);
- }
- var getters: [put_thread_count]*std.os.Thread = undefined;
- for (getters) |*t| {
- t.* = try std.os.spawnThread(&context, startGets);
- }
+ if (builtin.single_threaded) {
+ {
+ var i: usize = 0;
+ while (i < put_thread_count) : (i += 1) {
+ std.debug.assertOrPanic(startPuts(&context) == 0);
+ }
+ }
+ context.puts_done = 1;
+ {
+ var i: usize = 0;
+ while (i < put_thread_count) : (i += 1) {
+ std.debug.assertOrPanic(startGets(&context) == 0);
+ }
+ }
+ } else {
+ var putters: [put_thread_count]*std.os.Thread = undefined;
+ for (putters) |*t| {
+ t.* = try std.os.spawnThread(&context, startPuts);
+ }
+ var getters: [put_thread_count]*std.os.Thread = undefined;
+ for (getters) |*t| {
+ t.* = try std.os.spawnThread(&context, startGets);
+ }
- for (putters) |t|
- t.wait();
- _ = @atomicRmw(u8, &context.puts_done, builtin.AtomicRmwOp.Xchg, 1, AtomicOrder.SeqCst);
- for (getters) |t|
- t.wait();
+ for (putters) |t|
+ t.wait();
+ _ = @atomicRmw(u8, &context.puts_done, builtin.AtomicRmwOp.Xchg, 1, AtomicOrder.SeqCst);
+ for (getters) |t|
+ t.wait();
+ }
if (context.put_sum != context.get_sum) {
std.debug.panic("failure\nput_sum:{} != get_sum:{}", context.put_sum, context.get_sum);
std/atomic/stack.zig
@@ -4,10 +4,13 @@ const AtomicOrder = builtin.AtomicOrder;
/// Many reader, many writer, non-allocating, thread-safe
/// Uses a spinlock to protect push() and pop()
+/// When building in single threaded mode, this is a simple linked list.
pub fn Stack(comptime T: type) type {
return struct {
root: ?*Node,
- lock: u8,
+ lock: @typeOf(lock_init),
+
+ const lock_init = if (builtin.single_threaded) {} else u8(0);
pub const Self = @This();
@@ -19,7 +22,7 @@ pub fn Stack(comptime T: type) type {
pub fn init() Self {
return Self{
.root = null,
- .lock = 0,
+ .lock = lock_init,
};
}
@@ -31,20 +34,31 @@ pub fn Stack(comptime T: type) type {
}
pub fn push(self: *Self, node: *Node) void {
- while (@atomicRmw(u8, &self.lock, builtin.AtomicRmwOp.Xchg, 1, AtomicOrder.SeqCst) != 0) {}
- defer assert(@atomicRmw(u8, &self.lock, builtin.AtomicRmwOp.Xchg, 0, AtomicOrder.SeqCst) == 1);
-
- node.next = self.root;
- self.root = node;
+ if (builtin.single_threaded) {
+ node.next = self.root;
+ self.root = node;
+ } else {
+ while (@atomicRmw(u8, &self.lock, builtin.AtomicRmwOp.Xchg, 1, AtomicOrder.SeqCst) != 0) {}
+ defer assert(@atomicRmw(u8, &self.lock, builtin.AtomicRmwOp.Xchg, 0, AtomicOrder.SeqCst) == 1);
+
+ node.next = self.root;
+ self.root = node;
+ }
}
pub fn pop(self: *Self) ?*Node {
- while (@atomicRmw(u8, &self.lock, builtin.AtomicRmwOp.Xchg, 1, AtomicOrder.SeqCst) != 0) {}
- defer assert(@atomicRmw(u8, &self.lock, builtin.AtomicRmwOp.Xchg, 0, AtomicOrder.SeqCst) == 1);
-
- const root = self.root orelse return null;
- self.root = root.next;
- return root;
+ if (builtin.single_threaded) {
+ const root = self.root orelse return null;
+ self.root = root.next;
+ return root;
+ } else {
+ while (@atomicRmw(u8, &self.lock, builtin.AtomicRmwOp.Xchg, 1, AtomicOrder.SeqCst) != 0) {}
+ defer assert(@atomicRmw(u8, &self.lock, builtin.AtomicRmwOp.Xchg, 0, AtomicOrder.SeqCst) == 1);
+
+ const root = self.root orelse return null;
+ self.root = root.next;
+ return root;
+ }
}
pub fn isEmpty(self: *Self) bool {
@@ -90,20 +104,36 @@ test "std.atomic.stack" {
.get_count = 0,
};
- var putters: [put_thread_count]*std.os.Thread = undefined;
- for (putters) |*t| {
- t.* = try std.os.spawnThread(&context, startPuts);
- }
- var getters: [put_thread_count]*std.os.Thread = undefined;
- for (getters) |*t| {
- t.* = try std.os.spawnThread(&context, startGets);
- }
+ if (builtin.single_threaded) {
+ {
+ var i: usize = 0;
+ while (i < put_thread_count) : (i += 1) {
+ std.debug.assertOrPanic(startPuts(&context) == 0);
+ }
+ }
+ context.puts_done = 1;
+ {
+ var i: usize = 0;
+ while (i < put_thread_count) : (i += 1) {
+ std.debug.assertOrPanic(startGets(&context) == 0);
+ }
+ }
+ } else {
+ var putters: [put_thread_count]*std.os.Thread = undefined;
+ for (putters) |*t| {
+ t.* = try std.os.spawnThread(&context, startPuts);
+ }
+ var getters: [put_thread_count]*std.os.Thread = undefined;
+ for (getters) |*t| {
+ t.* = try std.os.spawnThread(&context, startGets);
+ }
- for (putters) |t|
- t.wait();
- _ = @atomicRmw(u8, &context.puts_done, builtin.AtomicRmwOp.Xchg, 1, AtomicOrder.SeqCst);
- for (getters) |t|
- t.wait();
+ for (putters) |t|
+ t.wait();
+ _ = @atomicRmw(u8, &context.puts_done, builtin.AtomicRmwOp.Xchg, 1, AtomicOrder.SeqCst);
+ for (getters) |t|
+ t.wait();
+ }
if (context.put_sum != context.get_sum) {
std.debug.panic("failure\nput_sum:{} != get_sum:{}", context.put_sum, context.get_sum);
std/event/channel.zig
@@ -319,6 +319,9 @@ pub fn Channel(comptime T: type) type {
}
test "std.event.Channel" {
+ // https://github.com/ziglang/zig/issues/1908
+ if (builtin.single_threaded) return error.SkipZigTest;
+
var da = std.heap.DirectAllocator.init();
defer da.deinit();
std/event/future.zig
@@ -84,6 +84,9 @@ pub fn Future(comptime T: type) type {
}
test "std.event.Future" {
+ // https://github.com/ziglang/zig/issues/1908
+ if (builtin.single_threaded) return error.SkipZigTest;
+
var da = std.heap.DirectAllocator.init();
defer da.deinit();
std/event/group.zig
@@ -121,6 +121,9 @@ pub fn Group(comptime ReturnType: type) type {
}
test "std.event.Group" {
+ // https://github.com/ziglang/zig/issues/1908
+ if (builtin.single_threaded) return error.SkipZigTest;
+
var da = std.heap.DirectAllocator.init();
defer da.deinit();
std/event/lock.zig
@@ -122,6 +122,9 @@ pub const Lock = struct {
};
test "std.event.Lock" {
+ // https://github.com/ziglang/zig/issues/1908
+ if (builtin.single_threaded) return error.SkipZigTest;
+
var da = std.heap.DirectAllocator.init();
defer da.deinit();
std/event/loop.zig
@@ -97,6 +97,7 @@ pub const Loop = struct {
/// TODO copy elision / named return values so that the threads referencing *Loop
/// have the correct pointer value.
pub fn initMultiThreaded(self: *Loop, allocator: *mem.Allocator) !void {
+ if (builtin.single_threaded) @compileError("initMultiThreaded unavailable when building in single-threaded mode");
const core_count = try os.cpuCount(allocator);
return self.initInternal(allocator, core_count);
}
@@ -201,6 +202,11 @@ pub const Loop = struct {
self.os_data.fs_thread.wait();
}
+ if (builtin.single_threaded) {
+ assert(extra_thread_count == 0);
+ return;
+ }
+
var extra_thread_index: usize = 0;
errdefer {
// writing 8 bytes to an eventfd cannot fail
@@ -301,6 +307,11 @@ pub const Loop = struct {
self.os_data.fs_thread.wait();
}
+ if (builtin.single_threaded) {
+ assert(extra_thread_count == 0);
+ return;
+ }
+
var extra_thread_index: usize = 0;
errdefer {
_ = os.bsdKEvent(self.os_data.kqfd, final_kev_arr, empty_kevs, null) catch unreachable;
@@ -338,6 +349,11 @@ pub const Loop = struct {
self.available_eventfd_resume_nodes.push(eventfd_node);
}
+ if (builtin.single_threaded) {
+ assert(extra_thread_count == 0);
+ return;
+ }
+
var extra_thread_index: usize = 0;
errdefer {
var i: usize = 0;
@@ -845,6 +861,9 @@ pub const Loop = struct {
};
test "std.event.Loop - basic" {
+ // https://github.com/ziglang/zig/issues/1908
+ if (builtin.single_threaded) return error.SkipZigTest;
+
var da = std.heap.DirectAllocator.init();
defer da.deinit();
@@ -858,6 +877,9 @@ test "std.event.Loop - basic" {
}
test "std.event.Loop - call" {
+ // https://github.com/ziglang/zig/issues/1908
+ if (builtin.single_threaded) return error.SkipZigTest;
+
var da = std.heap.DirectAllocator.init();
defer da.deinit();
std/event/net.zig
@@ -269,6 +269,9 @@ pub async fn connect(loop: *Loop, _address: *const std.net.Address) !os.File {
}
test "listen on a port, send bytes, receive bytes" {
+ // https://github.com/ziglang/zig/issues/1908
+ if (builtin.single_threaded) return error.SkipZigTest;
+
if (builtin.os != builtin.Os.linux) {
// TODO build abstractions for other operating systems
return error.SkipZigTest;
std/event/rwlock.zig
@@ -211,6 +211,9 @@ pub const RwLock = struct {
};
test "std.event.RwLock" {
+ // https://github.com/ziglang/zig/issues/1908
+ if (builtin.single_threaded) return error.SkipZigTest;
+
var da = std.heap.DirectAllocator.init();
defer da.deinit();
std/os/index.zig
@@ -3013,6 +3013,7 @@ pub const SpawnThreadError = error{
/// where T is u8, noreturn, void, or !void
/// caller must call wait on the returned thread
pub fn spawnThread(context: var, comptime startFn: var) SpawnThreadError!*Thread {
+ if (builtin.single_threaded) @compileError("cannot spawn thread when building in single-threaded mode");
// TODO compile-time call graph analysis to determine stack upper bound
// https://github.com/ziglang/zig/issues/157
const default_stack_size = 8 * 1024 * 1024;
std/os/test.zig
@@ -40,6 +40,8 @@ fn testThreadIdFn(thread_id: *os.Thread.Id) void {
}
test "std.os.Thread.getCurrentId" {
+ if (builtin.single_threaded) return error.SkipZigTest;
+
var thread_current_id: os.Thread.Id = undefined;
const thread = try os.spawnThread(&thread_current_id, testThreadIdFn);
const thread_id = thread.handle();
@@ -53,6 +55,8 @@ test "std.os.Thread.getCurrentId" {
}
test "spawn threads" {
+ if (builtin.single_threaded) return error.SkipZigTest;
+
var shared_ctx: i32 = 1;
const thread1 = try std.os.spawnThread({}, start1);
std/mutex.zig
@@ -14,7 +14,36 @@ const windows = std.os.windows;
/// If you need static initialization, use std.StaticallyInitializedMutex.
/// The Linux implementation is based on mutex3 from
/// https://www.akkadia.org/drepper/futex.pdf
-pub const Mutex = switch(builtin.os) {
+/// When an application is built in single threaded release mode, all the functions are
+/// no-ops. In single threaded debug mode, there is deadlock detection.
+pub const Mutex = if (builtin.single_threaded)
+ struct {
+ lock: @typeOf(lock_init),
+
+ const lock_init = if (std.debug.runtime_safety) false else {};
+
+ pub const Held = struct {
+ mutex: *Mutex,
+
+ pub fn release(self: Held) void {
+ if (std.debug.runtime_safety) {
+ self.mutex.lock = false;
+ }
+ }
+ };
+ pub fn init() Mutex {
+ return Mutex{ .lock = lock_init };
+ }
+ pub fn deinit(self: *Mutex) void {}
+
+ pub fn acquire(self: *Mutex) Held {
+ if (std.debug.runtime_safety and self.lock) {
+ @panic("deadlock detected");
+ }
+ return Held{ .mutex = self };
+ }
+ }
+else switch (builtin.os) {
builtin.Os.linux => struct {
/// 0: unlocked
/// 1: locked, no waiters
@@ -39,9 +68,7 @@ pub const Mutex = switch(builtin.os) {
};
pub fn init() Mutex {
- return Mutex {
- .lock = 0,
- };
+ return Mutex{ .lock = 0 };
}
pub fn deinit(self: *Mutex) void {}
@@ -60,7 +87,7 @@ pub const Mutex = switch(builtin.os) {
}
c = @atomicRmw(i32, &self.lock, AtomicRmwOp.Xchg, 2, AtomicOrder.Acquire);
}
- return Held { .mutex = self };
+ return Held{ .mutex = self };
}
},
// TODO once https://github.com/ziglang/zig/issues/287 (copy elision) is solved, we can make a
@@ -78,21 +105,19 @@ pub const Mutex = switch(builtin.os) {
mutex: *Mutex,
pub fn release(self: Held) void {
- SpinLock.Held.release(SpinLock.Held { .spinlock = &self.mutex.lock });
+ SpinLock.Held.release(SpinLock.Held{ .spinlock = &self.mutex.lock });
}
};
pub fn init() Mutex {
- return Mutex {
- .lock = SpinLock.init(),
- };
+ return Mutex{ .lock = SpinLock.init() };
}
pub fn deinit(self: *Mutex) void {}
pub fn acquire(self: *Mutex) Held {
_ = self.lock.acquire();
- return Held { .mutex = self };
+ return Held{ .mutex = self };
}
},
};
@@ -122,15 +147,20 @@ test "std.Mutex" {
.data = 0,
};
- const thread_count = 10;
- var threads: [thread_count]*std.os.Thread = undefined;
- for (threads) |*t| {
- t.* = try std.os.spawnThread(&context, worker);
- }
- for (threads) |t|
- t.wait();
+ if (builtin.single_threaded) {
+ worker(&context);
+ std.debug.assertOrPanic(context.data == TestContext.incr_count);
+ } else {
+ const thread_count = 10;
+ var threads: [thread_count]*std.os.Thread = undefined;
+ for (threads) |*t| {
+ t.* = try std.os.spawnThread(&context, worker);
+ }
+ for (threads) |t|
+ t.wait();
- std.debug.assertOrPanic(context.data == thread_count * TestContext.incr_count);
+ std.debug.assertOrPanic(context.data == thread_count * TestContext.incr_count);
+ }
}
fn worker(ctx: *TestContext) void {
std/statically_initialized_mutex.zig
@@ -93,13 +93,18 @@ test "std.StaticallyInitializedMutex" {
.data = 0,
};
- const thread_count = 10;
- var threads: [thread_count]*std.os.Thread = undefined;
- for (threads) |*t| {
- t.* = try std.os.spawnThread(&context, TestContext.worker);
- }
- for (threads) |t|
- t.wait();
+ if (builtin.single_threaded) {
+ TestContext.worker(&context);
+ std.debug.assertOrPanic(context.data == TestContext.incr_count);
+ } else {
+ const thread_count = 10;
+ var threads: [thread_count]*std.os.Thread = undefined;
+ for (threads) |*t| {
+ t.* = try std.os.spawnThread(&context, TestContext.worker);
+ }
+ for (threads) |t|
+ t.wait();
- std.debug.assertOrPanic(context.data == thread_count * TestContext.incr_count);
+ std.debug.assertOrPanic(context.data == thread_count * TestContext.incr_count);
+ }
}
test/tests.zig
@@ -163,25 +163,32 @@ pub fn addPkgTests(b: *build.Builder, test_filter: ?[]const u8, root_src: []cons
for (test_targets) |test_target| {
const is_native = (test_target.os == builtin.os and test_target.arch == builtin.arch);
for (modes) |mode| {
- for ([]bool{
- false,
- true,
- }) |link_libc| {
- if (link_libc and !is_native) {
- // don't assume we have a cross-compiling libc set up
- continue;
- }
- const these_tests = b.addTest(root_src);
- these_tests.setNamePrefix(b.fmt("{}-{}-{}-{}-{} ", name, @tagName(test_target.os), @tagName(test_target.arch), @tagName(mode), if (link_libc) "c" else "bare"));
- these_tests.setFilter(test_filter);
- these_tests.setBuildMode(mode);
- if (!is_native) {
- these_tests.setTarget(test_target.arch, test_target.os, test_target.environ);
- }
- if (link_libc) {
- these_tests.linkSystemLibrary("c");
+ for ([]bool{ false, true }) |link_libc| {
+ for ([]bool{ false, true }) |single_threaded| {
+ if (link_libc and !is_native) {
+ // don't assume we have a cross-compiling libc set up
+ continue;
+ }
+ const these_tests = b.addTest(root_src);
+ these_tests.setNamePrefix(b.fmt(
+ "{}-{}-{}-{}-{}-{} ",
+ name,
+ @tagName(test_target.os),
+ @tagName(test_target.arch),
+ @tagName(mode),
+ if (link_libc) "c" else "bare",
+ if (single_threaded) "single" else "multi",
+ ));
+ these_tests.setFilter(test_filter);
+ these_tests.setBuildMode(mode);
+ if (!is_native) {
+ these_tests.setTarget(test_target.arch, test_target.os, test_target.environ);
+ }
+ if (link_libc) {
+ these_tests.linkSystemLibrary("c");
+ }
+ step.dependOn(&these_tests.step);
}
- step.dependOn(&these_tests.step);
}
}
}