从ThreadPoolExecutor重写用于日志记录的java函数
// code exactly taken from java concurrency in practice
public class TimingThreadPool extends ThreadPoolExecutor {
private final ThreadLocal<Long> startTime
= new ThreadLocal<Long>();
private final Logger log = Logger.getLogger("TimingThreadPool");
private final AtomicLong numTasks = new AtomicLong();
private final AtomicLong totalTime = new AtomicLong();
protected void beforeExecute(Thread t, Runnable r) {
super.beforeExecute(t, r);
log.fine(String.format("Thread %s: start %s", t, r));
startTime.set(System.nanoTime());
}
protected void afterExecute(Runnable r, Throwable t) {
try {
long endTime = System.nanoTime();
long taskTime = endTime - startTime.get();
numTasks.incrementAndGet();
totalTime.addAndGet(taskTime);
log.fine(String.format("Thread %s: end %s, time=%dns",
t, r, taskTime));
} finally {
super.afterExecute(r, t);
}
}
protected void terminated() {
try {
log.info(String.format("Terminated: avg time=%dns",
totalTime.get() / numTasks.get()));
} finally {
super.terminated();
}
}
}
是所有工作线程共享的ThreadPoolExecutor
实例。如果是,那么方法beforeExecute(...)
和afterExecute(...)
不应该同步吗?如果答案是否定的,那么原因是“局部变量被分配到线程堆栈中,状态变量如numtask、totalTime、startTime是线程受限/原子的”
# 1 楼答案
您不需要同步beforeExecute和afterExecute,因为这两个方法中使用的所有字段都是线程安全的java。util。登录中。Logger(来自API-Logger上的所有方法都是多线程安全的。)或者ThreadLocal和AtocmicLong专门为免锁使用而设计
至于局部变量,它们只被一个线程访问,不需要任何同步