Netty杂记

// 源码位置: io.netty.channel.nio.NioEventLoop#run
@Override
protected void run() {
    int selectCnt = 0;
    for (;;) {
        try {
            int strategy;
            try {
                strategy = selectStrategy.calculateStrategy(selectNowSupplier, hasTasks());
                // 1.轮询IO事件
                strategy = select(curDeadlineNanos);
            } catch (IOException e) {
                ...
            }
            ...
            if (ioRatio == 100) {
                ...
            } else if (strategy > 0) {
                final long ioStartTime = System.nanoTime();
                try {
                    // 2.处理IO事件
                    processSelectedKeys();
                } finally {
                    // Ensure we always run tasks.
                    final long ioTime = System.nanoTime() - ioStartTime;
                    // 3.执行任务
                    ranTasks = runAllTasks(ioTime * (100 - ioRatio) / ioRatio);
                }
            }
        ...
        }
    }
}    
    

/**
 * Poll all tasks from the task queue and run them via {@link Runnable#run()} method.  This method stops running the tasks in the task queue and returns if it ran longer than {@code timeoutNanos}.
 */
protected boolean runAllTasks(long timeoutNanos) {    
    fetchFromScheduledTaskQueue();
    Runnable task = pollTask();
    if (task == null) {
        afterRunningAllTasks();
        return false;
    }

    final long deadline = timeoutNanos > 0 ? ScheduledFutureTask.nanoTime() + timeoutNanos : 0;
    long runTasks = 0;
    long lastExecutionTime;
    for (;;) {
        safeExecute(task);

        runTasks ++;

        // 每64个任务检查一次超时,因为nanoTime()比较昂贵.
        // Check timeout every 64 tasks because nanoTime() is relatively expensive.
        // XXX: Hard-coded value - will make it configurable if it is really a problem.
        if ((runTasks & 0x3F) == 0) {
            lastExecutionTime = ScheduledFutureTask.nanoTime();
            if (lastExecutionTime >= deadline) {
                break;
            }
        }

        task = pollTask();
        if (task == null) {
            lastExecutionTime = ScheduledFutureTask.nanoTime();
            break;
        }
    }

    afterRunningAllTasks();
    this.lastExecutionTime = lastExecutionTime;
    return true;
}

// 源码位置: java.lang.System#nanoTime
public static native long nanoTime();

// 源码位置: hotspot/src/share/vm/prims/jvm.cpp
JVM_LEAF(jlong, JVM_NanoTime(JNIEnv *env, jclass ignored))
  JVMWrapper("JVM_NanoTime");
  return os::javaTimeNanos();
JVM_END

// 源码位置: hotspot/src/os/linux/vm/os_linux.cpp
jlong os::javaTimeNanos() {
  if (Linux::supports_monotonic_clock()) {
    struct timespec tp;
    // 系统调用
    int status = Linux::clock_gettime(CLOCK_MONOTONIC, &tp);
    assert(status == 0, "gettime error");
    jlong result = jlong(tp.tv_sec) * (1000 * 1000 * 1000) + jlong(tp.tv_nsec);
    return result;
  } else {
    timeval time;
    // 调用C库函数,底层调用系统调用
    int status = gettimeofday(&time, NULL);
    assert(status != -1, "linux error");
    jlong usecs = jlong(time.tv_sec) * (1000 * 1000) + jlong(time.tv_usec);
    return 1000 * usecs;
  }
}

public class Example {

    public static void main(String[] args) {
        System.out.println("start...");
        
        long l = System.nanoTime();
        System.out.println(l);
        
        System.out.println("end...");
    }
}

[v-dev: tmp]# strace -ff -o out java Example
start...
35737962287000
end...

write(1, "start...", 8)                 = 8
gettimeofday({tv_sec=1638243469, tv_usec=142774}, NULL) = 0
write(1, "\n", 1)                       = 1
clock_gettime(CLOCK_MONOTONIC, {tv_sec=35737, tv_nsec=962287000}) = 0
gettimeofday({tv_sec=1638243469, tv_usec=143295}, NULL) = 0
gettimeofday({tv_sec=1638243469, tv_usec=143447}, NULL) = 0
gettimeofday({tv_sec=1638243469, tv_usec=143568}, NULL) = 0
write(1, "35737962287000", 14)          = 14
write(1, "\n", 1)                       = 1
write(1, "end...", 6)                   = 6
write(1, "\n", 1)                       = 1

<dependency>
  <groupId>cn.hutool</groupId>
  <artifactId>hutool-all</artifactId>
  <version>5.3.10</version>
</dependency>

private long genTime() {
    return System.currentTimeMillis();
}

private long genTime() {
    return this.useSystemClock ? SystemClock.now() : System.currentTimeMillis();
}