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/*
* Copyright (C) 2006 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.
*/
package android.os;
/**
* Core timekeeping facilities.
*
* <p> Three different clocks are available, and they should not be confused:
*
* <ul>
* <li> <p> {@link System#currentTimeMillis System.currentTimeMillis()}
* is the standard "wall" clock (time and date) expressing milliseconds
* since the epoch. The wall clock can be set by the user or the phone
* network (see {@link #setCurrentTimeMillis}), so the time may jump
* backwards or forwards unpredictably. This clock should only be used
* when correspondence with real-world dates and times is important, such
* as in a calendar or alarm clock application. Interval or elapsed
* time measurements should use a different clock. If you are using
* System.currentTimeMillis(), consider listening to the
* {@link android.content.Intent#ACTION_TIME_TICK ACTION_TIME_TICK},
* {@link android.content.Intent#ACTION_TIME_CHANGED ACTION_TIME_CHANGED}
* and {@link android.content.Intent#ACTION_TIMEZONE_CHANGED
* ACTION_TIMEZONE_CHANGED} {@link android.content.Intent Intent}
* broadcasts to find out when the time changes.
*
* <li> <p> {@link #uptimeMillis} is counted in milliseconds since the
* system was booted. This clock stops when the system enters deep
* sleep (CPU off, display dark, device waiting for external input),
* but is not affected by clock scaling, idle, or other power saving
* mechanisms. This is the basis for most interval timing
* such as {@link Thread#sleep(long) Thread.sleep(millls)},
* {@link Object#wait(long) Object.wait(millis)}, and
* {@link System#nanoTime System.nanoTime()}. This clock is guaranteed
* to be monotonic, and is the recommended basis for the general purpose
* interval timing of user interface events, performance measurements,
* and anything else that does not need to measure elapsed time during
* device sleep. Most methods that accept a timestamp value expect the
* {@link #uptimeMillis} clock.
*
* <li> <p> {@link #elapsedRealtime} is counted in milliseconds since the
* system was booted, including deep sleep. This clock should be used
* when measuring time intervals that may span periods of system sleep.
* </ul>
*
* There are several mechanisms for controlling the timing of events:
*
* <ul>
* <li> <p> Standard functions like {@link Thread#sleep(long)
* Thread.sleep(millis)} and {@link Object#wait(long) Object.wait(millis)}
* are always available. These functions use the {@link #uptimeMillis}
* clock; if the device enters sleep, the remainder of the time will be
* postponed until the device wakes up. These synchronous functions may
* be interrupted with {@link Thread#interrupt Thread.interrupt()}, and
* you must handle {@link InterruptedException}.
*
* <li> <p> {@link #sleep SystemClock.sleep(millis)} is a utility function
* very similar to {@link Thread#sleep(long) Thread.sleep(millis)}, but it
* ignores {@link InterruptedException}. Use this function for delays if
* you do not use {@link Thread#interrupt Thread.interrupt()}, as it will
* preserve the interrupted state of the thread.
*
* <li> <p> The {@link android.os.Handler} class can schedule asynchronous
* callbacks at an absolute or relative time. Handler objects also use the
* {@link #uptimeMillis} clock, and require an {@link android.os.Looper
* event loop} (normally present in any GUI application).
*
* <li> <p> The {@link android.app.AlarmManager} can trigger one-time or
* recurring events which occur even when the device is in deep sleep
* or your application is not running. Events may be scheduled with your
* choice of {@link java.lang.System#currentTimeMillis} (RTC) or
* {@link #elapsedRealtime} (ELAPSED_REALTIME), and cause an
* {@link android.content.Intent} broadcast when they occur.
* </ul>
*/
public final class SystemClock {
/**
* This class is uninstantiable.
*/
private SystemClock() {
// This space intentionally left blank.
}
/**
* Waits a given number of milliseconds (of uptimeMillis) before returning.
* Similar to {@link java.lang.Thread#sleep(long)}, but does not throw
* {@link InterruptedException}; {@link Thread#interrupt()} events are
* deferred until the next interruptible operation. Does not return until
* at least the specified number of milliseconds has elapsed.
*
* @param ms to sleep before returning, in milliseconds of uptime.
*/
public static void sleep(long ms)
{
long start = uptimeMillis();
long duration = ms;
boolean interrupted = false;
do {
try {
Thread.sleep(duration);
}
catch (InterruptedException e) {
interrupted = true;
}
duration = start + ms - uptimeMillis();
} while (duration > 0);
if (interrupted) {
// Important: we don't want to quietly eat an interrupt() event,
// so we make sure to re-interrupt the thread so that the next
// call to Thread.sleep() or Object.wait() will be interrupted.
Thread.currentThread().interrupt();
}
}
/**
* Sets the current wall time, in milliseconds. Requires the calling
* process to have appropriate permissions.
*
* @return if the clock was successfully set to the specified time.
*/
native public static boolean setCurrentTimeMillis(long millis);
/**
* Returns milliseconds since boot, not counting time spent in deep sleep.
* <b>Note:</b> This value may get reset occasionally (before it would
* otherwise wrap around).
*
* @return milliseconds of non-sleep uptime since boot.
*/
native public static long uptimeMillis();
/**
* Returns milliseconds since boot, including time spent in sleep.
*
* @return elapsed milliseconds since boot.
*/
native public static long elapsedRealtime();
/**
* Returns milliseconds running in the current thread.
*
* @return elapsed milliseconds in the thread
*/
public static native long currentThreadTimeMillis();
}
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