1 // Copyright 2017 The Chromium Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
4
5 #include "mojo/public/cpp/system/simple_watcher.h"
6
7 #include "base/bind.h"
8 #include "base/macros.h"
9 #include "base/memory/ptr_util.h"
10 #include "base/sequenced_task_runner.h"
11 #include "base/single_thread_task_runner.h"
12 #include "base/synchronization/lock.h"
13 #include "base/threading/thread_task_runner_handle.h"
14 #include "base/trace_event/heap_profiler.h"
15 #include "mojo/public/c/system/trap.h"
16
17 namespace mojo {
18
19 // Thread-safe Context object used to schedule trap events from arbitrary
20 // threads.
21 class SimpleWatcher::Context : public base::RefCountedThreadSafe<Context> {
22 public:
23 // Creates a |Context| instance for a new watch on |watcher|, to observe
24 // |signals| on |handle|.
Create(base::WeakPtr<SimpleWatcher> watcher,scoped_refptr<base::SequencedTaskRunner> task_runner,TrapHandle trap_handle,Handle handle,MojoHandleSignals signals,MojoTriggerCondition condition,int watch_id,MojoResult * result)25 static scoped_refptr<Context> Create(
26 base::WeakPtr<SimpleWatcher> watcher,
27 scoped_refptr<base::SequencedTaskRunner> task_runner,
28 TrapHandle trap_handle,
29 Handle handle,
30 MojoHandleSignals signals,
31 MojoTriggerCondition condition,
32 int watch_id,
33 MojoResult* result) {
34 scoped_refptr<Context> context =
35 new Context(watcher, task_runner, watch_id);
36
37 // If MojoAddTrigger succeeds, it effectively assumes ownership of a
38 // reference to |context|. In that case, this reference is balanced in
39 // CallNotify() when |result| is |MOJO_RESULT_CANCELLED|.
40 context->AddRef();
41
42 *result = MojoAddTrigger(trap_handle.value(), handle.value(), signals,
43 condition, context->value(), nullptr);
44 if (*result != MOJO_RESULT_OK) {
45 // Balanced by the AddRef() above since MojoAddTrigger failed.
46 context->Release();
47 return nullptr;
48 }
49
50 return context;
51 }
52
CallNotify(const MojoTrapEvent * event)53 static void CallNotify(const MojoTrapEvent* event) {
54 auto* context = reinterpret_cast<Context*>(event->trigger_context);
55 context->Notify(event->result, event->signals_state, event->flags);
56
57 // The trigger was removed. We can release the ref it owned, which in turn
58 // may delete the Context.
59 if (event->result == MOJO_RESULT_CANCELLED)
60 context->Release();
61 }
62
value() const63 uintptr_t value() const { return reinterpret_cast<uintptr_t>(this); }
64
DisableCancellationNotifications()65 void DisableCancellationNotifications() {
66 base::AutoLock lock(lock_);
67 enable_cancellation_notifications_ = false;
68 }
69
70 private:
71 friend class base::RefCountedThreadSafe<Context>;
72
Context(base::WeakPtr<SimpleWatcher> weak_watcher,scoped_refptr<base::SequencedTaskRunner> task_runner,int watch_id)73 Context(base::WeakPtr<SimpleWatcher> weak_watcher,
74 scoped_refptr<base::SequencedTaskRunner> task_runner,
75 int watch_id)
76 : weak_watcher_(weak_watcher),
77 task_runner_(task_runner),
78 watch_id_(watch_id) {}
~Context()79 ~Context() {}
80
Notify(MojoResult result,MojoHandleSignalsState signals_state,MojoTrapEventFlags flags)81 void Notify(MojoResult result,
82 MojoHandleSignalsState signals_state,
83 MojoTrapEventFlags flags) {
84 if (result == MOJO_RESULT_CANCELLED) {
85 // The SimpleWatcher may have explicitly removed this trigger, so we don't
86 // bother dispatching the notification - it would be ignored anyway.
87 //
88 // TODO(rockot): This shouldn't really be necessary, but there are already
89 // instances today where bindings object may be bound and subsequently
90 // closed due to pipe error, all before the thread's TaskRunner has been
91 // properly initialized.
92 base::AutoLock lock(lock_);
93 if (!enable_cancellation_notifications_)
94 return;
95 }
96
97 HandleSignalsState state(signals_state.satisfied_signals,
98 signals_state.satisfiable_signals);
99 if (!(flags & MOJO_TRAP_EVENT_FLAG_WITHIN_API_CALL) &&
100 task_runner_->RunsTasksInCurrentSequence() && weak_watcher_ &&
101 weak_watcher_->is_default_task_runner_) {
102 // System notifications will trigger from the task runner passed to
103 // mojo::core::ScopedIPCSupport. In Chrome this happens to always be
104 // the default task runner for the IO thread.
105 weak_watcher_->OnHandleReady(watch_id_, result, state);
106 } else {
107 task_runner_->PostTask(
108 FROM_HERE, base::Bind(&SimpleWatcher::OnHandleReady, weak_watcher_,
109 watch_id_, result, state));
110 }
111 }
112
113 const base::WeakPtr<SimpleWatcher> weak_watcher_;
114 const scoped_refptr<base::SequencedTaskRunner> task_runner_;
115 const int watch_id_;
116
117 base::Lock lock_;
118 bool enable_cancellation_notifications_ = true;
119
120 DISALLOW_COPY_AND_ASSIGN(Context);
121 };
122
SimpleWatcher(const base::Location & from_here,ArmingPolicy arming_policy,scoped_refptr<base::SequencedTaskRunner> runner)123 SimpleWatcher::SimpleWatcher(const base::Location& from_here,
124 ArmingPolicy arming_policy,
125 scoped_refptr<base::SequencedTaskRunner> runner)
126 : arming_policy_(arming_policy),
127 task_runner_(std::move(runner)),
128 is_default_task_runner_(base::ThreadTaskRunnerHandle::IsSet() &&
129 task_runner_ ==
130 base::ThreadTaskRunnerHandle::Get()),
131 heap_profiler_tag_(from_here.file_name()),
132 weak_factory_(this) {
133 MojoResult rv = CreateTrap(&Context::CallNotify, &trap_handle_);
134 DCHECK_EQ(MOJO_RESULT_OK, rv);
135 DCHECK(task_runner_->RunsTasksInCurrentSequence());
136 }
137
~SimpleWatcher()138 SimpleWatcher::~SimpleWatcher() {
139 if (IsWatching())
140 Cancel();
141 }
142
IsWatching() const143 bool SimpleWatcher::IsWatching() const {
144 DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
145 return context_ != nullptr;
146 }
147
Watch(Handle handle,MojoHandleSignals signals,MojoTriggerCondition condition,const ReadyCallbackWithState & callback)148 MojoResult SimpleWatcher::Watch(Handle handle,
149 MojoHandleSignals signals,
150 MojoTriggerCondition condition,
151 const ReadyCallbackWithState& callback) {
152 DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
153 DCHECK(!IsWatching());
154 DCHECK(!callback.is_null());
155
156 callback_ = callback;
157 handle_ = handle;
158 watch_id_ += 1;
159
160 MojoResult result = MOJO_RESULT_UNKNOWN;
161 context_ = Context::Create(weak_factory_.GetWeakPtr(), task_runner_,
162 trap_handle_.get(), handle_, signals, condition,
163 watch_id_, &result);
164 if (!context_) {
165 handle_.set_value(kInvalidHandleValue);
166 callback_.Reset();
167 DCHECK_EQ(MOJO_RESULT_INVALID_ARGUMENT, result);
168 return result;
169 }
170
171 if (arming_policy_ == ArmingPolicy::AUTOMATIC)
172 ArmOrNotify();
173
174 return MOJO_RESULT_OK;
175 }
176
Cancel()177 void SimpleWatcher::Cancel() {
178 DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
179
180 // The watcher may have already been cancelled if the handle was closed.
181 if (!context_)
182 return;
183
184 // Prevent the cancellation notification from being dispatched to
185 // OnHandleReady() when cancellation is explicit. See the note in the
186 // implementation of DisableCancellationNotifications() above.
187 context_->DisableCancellationNotifications();
188
189 handle_.set_value(kInvalidHandleValue);
190 callback_.Reset();
191
192 // Ensure |context_| is unset by the time we call MojoRemoveTrigger, as it may
193 // re-enter the notification callback and we want to ensure |context_| is
194 // unset by then.
195 scoped_refptr<Context> context;
196 std::swap(context, context_);
197 MojoResult rv =
198 MojoRemoveTrigger(trap_handle_.get().value(), context->value(), nullptr);
199
200 // It's possible this cancellation could race with a handle closure
201 // notification, in which case the watch may have already been implicitly
202 // cancelled.
203 DCHECK(rv == MOJO_RESULT_OK || rv == MOJO_RESULT_NOT_FOUND);
204 }
205
Arm(MojoResult * ready_result,HandleSignalsState * ready_state)206 MojoResult SimpleWatcher::Arm(MojoResult* ready_result,
207 HandleSignalsState* ready_state) {
208 DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
209 uint32_t num_blocking_events = 1;
210 MojoTrapEvent blocking_event = {sizeof(blocking_event)};
211 MojoResult rv = MojoArmTrap(trap_handle_.get().value(), nullptr,
212 &num_blocking_events, &blocking_event);
213 if (rv == MOJO_RESULT_FAILED_PRECONDITION) {
214 DCHECK(context_);
215 DCHECK_EQ(1u, num_blocking_events);
216 DCHECK_EQ(context_->value(), blocking_event.trigger_context);
217 if (ready_result)
218 *ready_result = blocking_event.result;
219 if (ready_state) {
220 *ready_state =
221 HandleSignalsState(blocking_event.signals_state.satisfied_signals,
222 blocking_event.signals_state.satisfiable_signals);
223 }
224 }
225
226 return rv;
227 }
228
ArmOrNotify()229 void SimpleWatcher::ArmOrNotify() {
230 DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
231
232 // Already cancelled, nothing to do.
233 if (!IsWatching())
234 return;
235
236 MojoResult ready_result;
237 HandleSignalsState ready_state;
238 MojoResult rv = Arm(&ready_result, &ready_state);
239 if (rv == MOJO_RESULT_OK)
240 return;
241
242 DCHECK_EQ(MOJO_RESULT_FAILED_PRECONDITION, rv);
243 task_runner_->PostTask(
244 FROM_HERE,
245 base::Bind(&SimpleWatcher::OnHandleReady, weak_factory_.GetWeakPtr(),
246 watch_id_, ready_result, ready_state));
247 }
248
OnHandleReady(int watch_id,MojoResult result,const HandleSignalsState & state)249 void SimpleWatcher::OnHandleReady(int watch_id,
250 MojoResult result,
251 const HandleSignalsState& state) {
252 DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
253
254 // This notification may be for a previously watched context, in which case
255 // we just ignore it.
256 if (watch_id != watch_id_)
257 return;
258
259 ReadyCallbackWithState callback = callback_;
260 if (result == MOJO_RESULT_CANCELLED) {
261 // Implicit cancellation due to someone closing the watched handle. We clear
262 // the SimppleWatcher's state before dispatching this.
263 context_ = nullptr;
264 handle_.set_value(kInvalidHandleValue);
265 callback_.Reset();
266 }
267
268 // NOTE: It's legal for |callback| to delete |this|.
269 if (!callback.is_null()) {
270 TRACE_HEAP_PROFILER_API_SCOPED_TASK_EXECUTION event(heap_profiler_tag_);
271
272 base::WeakPtr<SimpleWatcher> weak_self = weak_factory_.GetWeakPtr();
273 callback.Run(result, state);
274 if (!weak_self)
275 return;
276
277 // Prevent |MOJO_RESULT_FAILED_PRECONDITION| task spam by only notifying
278 // at most once in AUTOMATIC arming mode.
279 if (result == MOJO_RESULT_FAILED_PRECONDITION)
280 return;
281
282 if (arming_policy_ == ArmingPolicy::AUTOMATIC && IsWatching())
283 ArmOrNotify();
284 }
285 }
286
287 } // namespace mojo
288