authorgravatar for andrew@ziglang.orgAndrew Kelley <andrew@ziglang.org> 2019-12-22 23:39:13-05:00
committergravatar for noreply@github.comGitHub <noreply@github.com> 2019-12-22 23:39:13-05:00
log25e71216c4640a3d88c8f63912ea574ad6fa004c
tree172dbe007066e3f39f6455f5b0c54d935e1d933a
parentad92227516bf977a3be2802db525ac2d678acc7c
parent1c5a1284e3992555653a01903bc3131c4b628e86
signature Signed by PGP key 4AEE18F83AFDEB23

Merge pull request #3974 from kprotty/event_broadcast

ResetEvent fixes & broadcast notify

3 files changed, 87 insertions(+), 39 deletions(-)

lib/std/c.zig+1
......@@ -220,6 +220,7 @@ pub const PTHREAD_COND_INITIALIZER = pthread_cond_t{};
220220pub extern "c" fn pthread_cond_wait(noalias cond: *pthread_cond_t, noalias mutex: *pthread_mutex_t) c_int;
221221pub extern "c" fn pthread_cond_timedwait(noalias cond: *pthread_cond_t, noalias mutex: *pthread_mutex_t, noalias abstime: *const timespec) c_int;
222222pub extern "c" fn pthread_cond_signal(cond: *pthread_cond_t) c_int;
223pub extern "c" fn pthread_cond_broadcast(cond: *pthread_cond_t) c_int;
223224pub extern "c" fn pthread_cond_destroy(cond: *pthread_cond_t) c_int;
224225
225226pub const pthread_t = *@OpaqueType();
lib/std/mutex.zig+24-4
......@@ -1,6 +1,8 @@
11const std = @import("std.zig");
22const builtin = @import("builtin");
33const os = std.os;
4const assert = std.debug.assert;
5const windows = os.windows;
46const testing = std.testing;
57const SpinLock = std.SpinLock;
68const ResetEvent = std.ResetEvent;
......@@ -73,20 +75,33 @@ else if (builtin.os == .windows)
7375 return self.tryAcquire() orelse self.acquireSlow();
7476 }
7577
78 fn acquireSpinning(self: *Mutex) Held {
79 @setCold(true);
80 while (true) : (SpinLock.yield()) {
81 return self.tryAcquire() orelse continue;
82 }
83 }
84
7685 fn acquireSlow(self: *Mutex) Held {
86 // try to use NT keyed events for blocking, falling back to spinlock if unavailable
7787 @setCold(true);
88 const handle = ResetEvent.OsEvent.Futex.getEventHandle() orelse return self.acquireSpinning();
89 const key = @ptrCast(*const c_void, &self.waiters);
90
7891 while (true) : (SpinLock.loopHint(1)) {
7992 const waiters = @atomicLoad(u32, &self.waiters, .Monotonic);
8093
8194 // try and take lock if unlocked
8295 if ((waiters & 1) == 0) {
83 if (@atomicRmw(u8, &self.locked, .Xchg, 1, .Acquire) == 0)
96 if (@atomicRmw(u8, &self.locked, .Xchg, 1, .Acquire) == 0) {
8497 return Held{ .mutex = self };
98 }
8599
86100 // otherwise, try and update the waiting count.
87101 // then unset the WAKE bit so that another unlocker can wake up a thread.
88102 } else if (@cmpxchgWeak(u32, &self.waiters, waiters, (waiters + WAIT) | 1, .Monotonic, .Monotonic) == null) {
89 ResetEvent.OsEvent.Futex.wait(@ptrCast(*i32, &self.waiters), undefined, null) catch unreachable;
103 const rc = windows.ntdll.NtWaitForKeyedEvent(handle, key, windows.FALSE, null);
104 assert(rc == 0);
90105 _ = @atomicRmw(u32, &self.waiters, .Sub, WAKE, .Monotonic);
91106 }
92107 }
......@@ -98,6 +113,8 @@ else if (builtin.os == .windows)
98113 pub fn release(self: Held) void {
99114 // unlock without a rmw/cmpxchg instruction
100115 @atomicStore(u8, @ptrCast(*u8, &self.mutex.locked), 0, .Release);
116 const handle = ResetEvent.OsEvent.Futex.getEventHandle() orelse return;
117 const key = @ptrCast(*const c_void, &self.mutex.waiters);
101118
102119 while (true) : (SpinLock.loopHint(1)) {
103120 const waiters = @atomicLoad(u32, &self.mutex.waiters, .Monotonic);
......@@ -110,8 +127,11 @@ else if (builtin.os == .windows)
110127 if (waiters & WAKE != 0) return;
111128
112129 // try to decrease the waiter count & set the WAKE bit meaning a thread is waking up
113 if (@cmpxchgWeak(u32, &self.mutex.waiters, waiters, waiters - WAIT + WAKE, .Release, .Monotonic) == null)
114 return ResetEvent.OsEvent.Futex.wake(@ptrCast(*i32, &self.mutex.waiters));
130 if (@cmpxchgWeak(u32, &self.mutex.waiters, waiters, waiters - WAIT + WAKE, .Release, .Monotonic) == null) {
131 const rc = windows.ntdll.NtReleaseKeyedEvent(handle, key, windows.FALSE, null);
132 assert(rc == 0);
133 return;
134 }
115135 }
116136 }
117137 };
lib/std/reset_event.zig+62-35
......@@ -36,7 +36,7 @@ pub const ResetEvent = struct {
3636 }
3737
3838 /// Sets the event if not already set and
39 /// wakes up at least one thread waiting the event.
39 /// wakes up all the threads waiting on the event.
4040 pub fn set(self: *ResetEvent) void {
4141 return self.os_event.set();
4242 }
......@@ -135,7 +135,7 @@ const PosixEvent = struct {
135135
136136 if (!self.is_set) {
137137 self.is_set = true;
138 assert(c.pthread_cond_signal(&self.cond) == 0);
138 assert(c.pthread_cond_broadcast(&self.cond) == 0);
139139 }
140140 }
141141
......@@ -181,40 +181,39 @@ const PosixEvent = struct {
181181};
182182
183183const AtomicEvent = struct {
184 state: State,
184 waiters: u32,
185185
186 const State = enum(i32) {
187 Empty,
188 Waiting,
189 Signaled,
190 };
186 const WAKE = 1 << 0;
187 const WAIT = 1 << 1;
191188
192189 fn init() AtomicEvent {
193 return AtomicEvent{ .state = .Empty };
190 return AtomicEvent{ .waiters = 0 };
194191 }
195192
196193 fn deinit(self: *AtomicEvent) void {
197194 self.* = undefined;
198195 }
199196
200 fn isSet(self: *AtomicEvent) bool {
201 return @atomicLoad(State, &self.state, .Acquire) == .Signaled;
197 fn isSet(self: *const AtomicEvent) bool {
198 return @atomicLoad(u32, &self.waiters, .Acquire) == WAKE;
202199 }
203200
204201 fn reset(self: *AtomicEvent) void {
205 @atomicStore(State, &self.state, .Empty, .Monotonic);
202 @atomicStore(u32, &self.waiters, 0, .Monotonic);
206203 }
207204
208205 fn set(self: *AtomicEvent) void {
209 if (@atomicRmw(State, &self.state, .Xchg, .Signaled, .Release) == .Waiting)
210 Futex.wake(@ptrCast(*i32, &self.state));
206 const waiters = @atomicRmw(u32, &self.waiters, .Xchg, WAKE, .Release);
207 if (waiters >= WAIT) {
208 return Futex.wake(&self.waiters, waiters >> 1);
209 }
211210 }
212211
213212 fn wait(self: *AtomicEvent, timeout: ?u64) !void {
214 var state = @atomicLoad(State, &self.state, .Monotonic);
215 while (state == .Empty) {
216 state = @cmpxchgWeak(State, &self.state, .Empty, .Waiting, .Acquire, .Monotonic) orelse
217 return Futex.wait(@ptrCast(*i32, &self.state), @enumToInt(State.Waiting), timeout);
213 var waiters = @atomicLoad(u32, &self.waiters, .Acquire);
214 while (waiters != WAKE) {
215 waiters = @cmpxchgWeak(u32, &self.waiters, waiters, waiters + WAIT, .Acquire, .Acquire)
216 orelse return Futex.wait(&self.waiters, timeout);
218217 }
219218 }
220219
......@@ -225,15 +224,15 @@ const AtomicEvent = struct {
225224 };
226225
227226 const SpinFutex = struct {
228 fn wake(ptr: *i32) void {}
227 fn wake(waiters: *u32, wake_count: u32) void {}
229228
230 fn wait(ptr: *i32, expected: i32, timeout: ?u64) !void {
229 fn wait(waiters: *u32, timeout: ?u64) !void {
231230 // TODO: handle platforms where a monotonic timer isnt available
232231 var timer: time.Timer = undefined;
233232 if (timeout != null)
234233 timer = time.Timer.start() catch unreachable;
235234
236 while (@atomicLoad(i32, ptr, .Acquire) == expected) {
235 while (@atomicLoad(u32, waiters, .Acquire) != WAKE) {
237236 SpinLock.yield();
238237 if (timeout) |timeout_ns| {
239238 if (timer.read() >= timeout_ns)
......@@ -244,12 +243,14 @@ const AtomicEvent = struct {
244243 };
245244
246245 const LinuxFutex = struct {
247 fn wake(ptr: *i32) void {
248 const rc = linux.futex_wake(ptr, linux.FUTEX_WAKE | linux.FUTEX_PRIVATE_FLAG, 1);
246 fn wake(waiters: *u32, wake_count: u32) void {
247 const waiting = std.math.maxInt(i32); // wake_count
248 const ptr = @ptrCast(*const i32, waiters);
249 const rc = linux.futex_wake(ptr, linux.FUTEX_WAKE | linux.FUTEX_PRIVATE_FLAG, waiting);
249250 assert(linux.getErrno(rc) == 0);
250251 }
251252
252 fn wait(ptr: *i32, expected: i32, timeout: ?u64) !void {
253 fn wait(waiters: *u32, timeout: ?u64) !void {
253254 var ts: linux.timespec = undefined;
254255 var ts_ptr: ?*linux.timespec = null;
255256 if (timeout) |timeout_ns| {
......@@ -258,7 +259,12 @@ const AtomicEvent = struct {
258259 ts.tv_nsec = @intCast(isize, timeout_ns % time.ns_per_s);
259260 }
260261
261 while (@atomicLoad(i32, ptr, .Acquire) == expected) {
262 while (true) {
263 const waiting = @atomicLoad(u32, waiters, .Acquire);
264 if (waiting == WAKE)
265 return;
266 const expected = @intCast(i32, waiting);
267 const ptr = @ptrCast(*const i32, waiters);
262268 const rc = linux.futex_wait(ptr, linux.FUTEX_WAIT | linux.FUTEX_PRIVATE_FLAG, expected, ts_ptr);
263269 switch (linux.getErrno(rc)) {
264270 0 => continue,
......@@ -272,15 +278,20 @@ const AtomicEvent = struct {
272278 };
273279
274280 const WindowsFutex = struct {
275 pub fn wake(ptr: *i32) void {
276 const handle = getEventHandle() orelse return SpinFutex.wake(ptr);
277 const key = @ptrCast(*const c_void, ptr);
278 const rc = windows.ntdll.NtReleaseKeyedEvent(handle, key, windows.FALSE, null);
279 assert(rc == 0);
281 pub fn wake(waiters: *u32, wake_count: u32) void {
282 const handle = getEventHandle() orelse return SpinFutex.wake(waiters, wake_count);
283 const key = @ptrCast(*const c_void, waiters);
284
285 var waiting = wake_count;
286 while (waiting != 0) : (waiting -= 1) {
287 const rc = windows.ntdll.NtReleaseKeyedEvent(handle, key, windows.FALSE, null);
288 assert(rc == 0);
289 }
280290 }
281291
282 pub fn wait(ptr: *i32, expected: i32, timeout: ?u64) !void {
283 const handle = getEventHandle() orelse return SpinFutex.wait(ptr, expected, timeout);
292 pub fn wait(waiters: *u32, timeout: ?u64) !void {
293 const handle = getEventHandle() orelse return SpinFutex.wait(waiters, timeout);
294 const key = @ptrCast(*const c_void, waiters);
284295
285296 // NT uses timeouts in units of 100ns with negative value being relative
286297 var timeout_ptr: ?*windows.LARGE_INTEGER = null;
......@@ -291,10 +302,26 @@ const AtomicEvent = struct {
291302 }
292303
293304 // NtWaitForKeyedEvent doesnt have spurious wake-ups
294 const key = @ptrCast(*const c_void, ptr);
295 const rc = windows.ntdll.NtWaitForKeyedEvent(handle, key, windows.FALSE, timeout_ptr);
305 var rc = windows.ntdll.NtWaitForKeyedEvent(handle, key, windows.FALSE, timeout_ptr);
296306 switch (rc) {
297 windows.WAIT_TIMEOUT => return error.TimedOut,
307 windows.WAIT_TIMEOUT => {
308 // update the wait count to signal that we're not waiting anymore.
309 // if the .set() thread already observed that we are, perform a
310 // matching NtWaitForKeyedEvent so that the .set() thread doesn't
311 // deadlock trying to run NtReleaseKeyedEvent above.
312 var waiting = @atomicLoad(u32, waiters, .Monotonic);
313 while (true) {
314 if (waiting == WAKE) {
315 rc = windows.ntdll.NtWaitForKeyedEvent(handle, key, windows.FALSE, null);
316 assert(rc == windows.WAIT_OBJECT_0);
317 break;
318 } else {
319 waiting = @cmpxchgWeak(u32, waiters, waiting, waiting - WAIT, .Acquire, .Monotonic) orelse break;
320 continue;
321 }
322 }
323 return error.TimedOut;
324 },
298325 windows.WAIT_OBJECT_0 => {},
299326 else => unreachable,
300327 }