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// Copyright 2017 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifdef UNSAFE_BUFFERS_BUILD
// TODO(crbug.com/351564777): Remove this and convert code to safer constructs.
#pragma allow_unsafe_buffers
#endif
#include "mojo/public/cpp/system/wait.h"
#include <memory>
#include <vector>
#include "base/memory/ptr_util.h"
#include "base/memory/ref_counted.h"
#include "base/synchronization/waitable_event.h"
#include "mojo/public/c/system/trap.h"
#include "mojo/public/cpp/system/trap.h"
namespace mojo {
namespace {
class TriggerContext : public base::RefCountedThreadSafe<TriggerContext> {
public:
TriggerContext()
: event_(base::WaitableEvent::ResetPolicy::AUTOMATIC,
base::WaitableEvent::InitialState::NOT_SIGNALED) {}
TriggerContext(const TriggerContext&) = delete;
TriggerContext& operator=(const TriggerContext&) = delete;
base::WaitableEvent& event() { return event_; }
MojoResult wait_result() const { return wait_result_; }
MojoHandleSignalsState wait_state() const { return wait_state_; }
uintptr_t context_value() const { return reinterpret_cast<uintptr_t>(this); }
static void OnNotification(const MojoTrapEvent* event) {
auto* context = reinterpret_cast<TriggerContext*>(event->trigger_context);
context->Notify(event->result, event->signals_state);
if (event->result == MOJO_RESULT_CANCELLED) {
// Balanced in Wait() or WaitMany().
context->Release();
}
}
private:
friend class base::RefCountedThreadSafe<TriggerContext>;
~TriggerContext() {}
void Notify(MojoResult result, MojoHandleSignalsState state) {
if (wait_result_ == MOJO_RESULT_UNKNOWN) {
wait_result_ = result;
wait_state_ = state;
}
event_.Signal();
}
base::WaitableEvent event_;
// NOTE: Although these are modified in Notify() which may be called from any
// sequence, Notify() is guaranteed to never run concurrently with itself.
// Furthermore, they are only modified once, before |event_| signals; so there
// is no need for a TriggerContext user to synchronize access to these fields
// apart from waiting on |event()|.
MojoResult wait_result_ = MOJO_RESULT_UNKNOWN;
MojoHandleSignalsState wait_state_ = {0, 0};
};
} // namespace
MojoResult Wait(Handle handle,
MojoHandleSignals signals,
MojoTriggerCondition condition,
MojoHandleSignalsState* signals_state) {
ScopedTrapHandle trap;
MojoResult rv = CreateTrap(&TriggerContext::OnNotification, &trap);
DCHECK_EQ(MOJO_RESULT_OK, rv);
scoped_refptr<TriggerContext> context = new TriggerContext;
// Balanced in TriggerContext::OnNotification if MojoAddTrigger() is
// successful. Otherwise balanced immediately below.
context->AddRef();
rv = MojoAddTrigger(trap.get().value(), handle.value(), signals, condition,
context->context_value(), nullptr);
if (rv == MOJO_RESULT_INVALID_ARGUMENT) {
// Balanced above.
context->Release();
return rv;
}
DCHECK_EQ(MOJO_RESULT_OK, rv);
uint32_t num_blocking_events = 1;
MojoTrapEvent blocking_event = {sizeof(blocking_event)};
rv = MojoArmTrap(trap.get().value(), nullptr, &num_blocking_events,
&blocking_event);
if (rv == MOJO_RESULT_FAILED_PRECONDITION) {
DCHECK_EQ(1u, num_blocking_events);
if (signals_state)
*signals_state = blocking_event.signals_state;
return blocking_event.result;
}
// Wait for the first notification only.
context->event().Wait();
MojoResult ready_result = context->wait_result();
DCHECK_NE(MOJO_RESULT_UNKNOWN, ready_result);
if (signals_state)
*signals_state = context->wait_state();
return ready_result;
}
MojoResult WaitMany(const Handle* handles,
const MojoHandleSignals* signals,
size_t num_handles,
size_t* result_index,
MojoHandleSignalsState* signals_states) {
if (!handles || !signals)
return MOJO_RESULT_INVALID_ARGUMENT;
ScopedTrapHandle trap;
MojoResult rv = CreateTrap(&TriggerContext::OnNotification, &trap);
DCHECK_EQ(MOJO_RESULT_OK, rv);
std::vector<scoped_refptr<TriggerContext>> contexts(num_handles);
std::vector<base::WaitableEvent*> events(num_handles);
for (size_t i = 0; i < num_handles; ++i) {
contexts[i] = new TriggerContext();
// Balanced in TriggerContext::OnNotification if MojoAddTrigger() is
// successful. Otherwise balanced immediately below.
contexts[i]->AddRef();
rv = MojoAddTrigger(trap.get().value(), handles[i].value(), signals[i],
MOJO_TRIGGER_CONDITION_SIGNALS_SATISFIED,
contexts[i]->context_value(), nullptr);
if (rv == MOJO_RESULT_INVALID_ARGUMENT) {
if (result_index)
*result_index = i;
// Balanced above.
contexts[i]->Release();
return MOJO_RESULT_INVALID_ARGUMENT;
}
events[i] = &contexts[i]->event();
}
uint32_t num_blocking_events = 1;
MojoTrapEvent blocking_event = {sizeof(blocking_event)};
rv = MojoArmTrap(trap.get().value(), nullptr, &num_blocking_events,
&blocking_event);
size_t index = num_handles;
MojoResult ready_result = MOJO_RESULT_UNKNOWN;
MojoHandleSignalsState ready_state = {};
if (rv == MOJO_RESULT_FAILED_PRECONDITION) {
DCHECK_EQ(1u, num_blocking_events);
// Most commonly we only watch a small number of handles. Just scan for
// the right index.
for (size_t i = 0; i < num_handles; ++i) {
if (contexts[i]->context_value() == blocking_event.trigger_context) {
index = i;
ready_result = blocking_event.result;
ready_state = blocking_event.signals_state;
break;
}
}
} else {
DCHECK_EQ(MOJO_RESULT_OK, rv);
// Wait for one of the contexts to signal. First one wins.
index = base::WaitableEvent::WaitMany(events.data(), events.size());
ready_result = contexts[index]->wait_result();
ready_state = contexts[index]->wait_state();
}
DCHECK_NE(MOJO_RESULT_UNKNOWN, ready_result);
DCHECK_LT(index, num_handles);
if (result_index)
*result_index = index;
if (signals_states) {
for (size_t i = 0; i < num_handles; ++i) {
if (i == index) {
signals_states[i] = ready_state;
} else {
signals_states[i] = handles[i].QuerySignalsState();
}
}
}
return ready_result;
}
} // namespace mojo
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