Android WatchDog

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本文介绍了Android系统中一个名为`Watchdog`的C++实现，它是一个资源管理工具，用于确保代码块在预设时间内执行完毕。如果超时，`Watchdog`会触发进程崩溃，发送SIGABRT信号。通过创建和销毁定时器，`Watchdog`在进入和退出代码块时进行监控，为关键操作提供时间限制保障。

一. Native C++ watchdog:

代码：

        frameworks/av/media/libwatchdog/include/watchdog/Watchdog.h
        frameworks/av/media/libwatchdog/Watchdog.cpp

Watchdog.h:

/*
 * Copyright (C) 2020 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef ANDROID_WATCHDOG_H
#define ANDROID_WATCHDOG_H

#include <chrono>
#include <time.h>

namespace android {

/*
 * An RAII-style object, which would crash the process if a timeout expires
 * before the object is destroyed.
 * The calling thread would be sent a SIGABORT, which would typically result in
 * a stack trace.
 *
 * Sample usage:
 * {
 *     Watchdog watchdog(std::chrono::milliseconds(10));
 *     DoSomething();
 * }
 * // If we got here, the function completed in time.
 */
class Watchdog final {
public:
    Watchdog(std::chrono::steady_clock::duration timeout);
    ~Watchdog();

private:
    timer_t mTimerId;
};

}  // namespace android

#endif  // ANDROID_WATCHDOG_H

Watchdog.cpp:

/*
 * Copyright (C) 2020 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#define LOG_TAG "Watchdog"

#include <watchdog/Watchdog.h>

#include <android-base/logging.h>
#include <android-base/threads.h>
#include <signal.h>
#include <time.h>
#include <cstring>
#include <utils/Log.h>

namespace android {

Watchdog::Watchdog(::std::chrono::steady_clock::duration timeout) {
    // Create the timer.
    struct sigevent sev;
    sev.sigev_notify = SIGEV_THREAD_ID;
    sev.sigev_notify_thread_id = base::GetThreadId();
    sev.sigev_signo = SIGABRT;
    sev.sigev_value.sival_ptr = &mTimerId;
    int err = timer_create(CLOCK_MONOTONIC, &sev, &mTimerId);
    if (err != 0) {
        PLOG(FATAL) << "Failed to create timer";
    }

    // Start the timer.
    struct itimerspec spec;
    memset(&spec, 0, sizeof(spec));
    auto ns = std::chrono::duration_cast<std::chrono::nanoseconds>(timeout);
    LOG_ALWAYS_FATAL_IF(timeout.count() <= 0, "Duration must be positive");
    spec.it_value.tv_sec = ns.count() / 1000000000;
    spec.it_value.tv_nsec = ns.count() % 1000000000;
    err = timer_settime(mTimerId, 0, &spec, nullptr);
    if (err != 0) {
        PLOG(FATAL) << "Failed to start timer";
    }
}

Watchdog::~Watchdog() {
    // Delete the timer.
    int err = timer_delete(mTimerId);
    if (err != 0) {
        PLOG(FATAL) << "Failed to delete timer";
    }
}

}  // namespace android

使用：发送的signal可以根据自己的需要来修改

#include <time.h>
#include "Watchdog.h"


int main(int argc, char** argv)
{
    // Watchdog在下面的代码块有效，
    // 如果在5s内，没有出代码块，就会狗叫，定时器就会给自己发送SIGABRT信号。
    // 如果在5s内出下面的代码块，就会调用Watchdog析构函数,timer_delete删除定时器。
    // 要旨：主要针对代码块，出代码块会析构
    {
        android::Watchdog watchdog(std::chrono::seconds(5));
        // 具体工作XXX
        sleep(6);
    }
    return 0;
}