/*
* 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;
/*-[
#include "libcore/io/ErrnoException.h"
#include <sys/types.h>
#include <sys/sysctl.h>
]-*/
/**
* 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.
*
* <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 suitable for interval timing when the
* interval does not span device sleep. Most methods that accept a
* timestamp value currently expect the {@link #uptimeMillis} clock.
*
* <li> <p> {@link #elapsedRealtime} and {@link #elapsedRealtimeNanos}
* return the time since the system was booted, and include deep sleep.
* This clock is guaranteed to be monotonic, and continues to tick even
* when the CPU is in power saving modes, so is the recommend basis
* for general purpose interval timing.
*
* </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.
* </ul>
*/
public final class SystemClock {
private static final String TAG = "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.
*/
public static boolean setCurrentTimeMillis(long millis) {
// TODO(tball): implement on iOS only if any customers need it.
return false;
}
/**
* Returns milliseconds since boot, not counting time spent in deep sleep.
*
* @return milliseconds of non-sleep uptime since boot.
*/
public static long uptimeMillis() {
return elapsedRealtime(); // Not aware of any iOS API to track deep sleep time.
}
/*-[
static long long boottime_usec() {
// MIB = Management Information Base (man sysctl).
#define MIB_SIZE 2
int mib[MIB_SIZE];
size_t size;
struct timeval boottime;
mib[0] = CTL_KERN;
mib[1] = KERN_BOOTTIME;
size = sizeof(boottime);
if (sysctl(mib, MIB_SIZE, &boottime, &size, NULL, 0) == -1) {
@throw AUTORELEASE([[LibcoreIoErrnoException alloc]
initWithNSString:@"sysctl" withInt:errno]);
}
return ((long long) boottime.tv_sec) * 1.e6 + boottime.tv_usec;
}
static long long uptime_usec() {
// source: http://stackoverflow.com/a/40497811
long long before_now;
long long after_now;
struct timeval now;
after_now = boottime_usec();
do {
before_now = after_now;
gettimeofday(&now, NULL);
after_now = boottime_usec();
} while (after_now != before_now);
return ((long long) now.tv_sec) * 1.e6 + now.tv_usec - before_now;
}
]-*/
/**
* Returns milliseconds since boot, including time spent in sleep.
*
* @return elapsed milliseconds since boot.
*/
public native static long elapsedRealtime() /*-[
return (long long)(uptime_usec() / 1000.0);
]-*/;
/**
* Returns nanoseconds since boot, including time spent in sleep.
*
* @return elapsed nanoseconds since boot.
*/
public static native long elapsedRealtimeNanos() /*-[
return uptime_usec() * 1000;
]-*/;
/**
* Returns current wall time in microseconds.
*
* @return elapsed microseconds in wall time
*
* @hide
*/
public static native long currentTimeMicro() /*-[
return (long long) [[NSDate date] timeIntervalSince1970];
]-*/;
// Not available on iOS.
/**
* Returns milliseconds running in the current thread.
*
* @return elapsed milliseconds in the thread
*
public static native long currentThreadTimeMillis();
/**
* Returns microseconds running in the current thread.
*
* @return elapsed microseconds in the thread
*
* @hide
*
public static native long currentThreadTimeMicro();
*/
}