util/concurrent/TimeUnit.java

/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain. Use, modify, and
 * redistribute this code in any way without acknowledgement.
 */

package java.util.concurrent;

/**
 * A <tt>TimeUnit</tt> represents time durations at a given unit of 
 * granularity and provides utility methods to convert across units, 
 * and to perform timing and delay operations in these units. 
 * <tt>TimeUnit</tt> is a &quot;featherweight&quot; class. 
 * It does not maintain time information, but only helps organize and 
 * use time representations that may be maintained separately across 
 * various contexts.
 * A static method {@link #nanoTime} provides access to a high
 * resolution, nanosecond, timer, which can be used to measure elapsed time.
 *
 * <p>The <tt>TimeUnit</tt> class cannot be directly instantiated.  
 * Use the {@link #SECONDS}, {@link #MILLISECONDS}, {@link #MICROSECONDS},
 * and {@link #NANOSECONDS} static instances that provide predefined
 * units of precision. If you use these frequently, consider
 * statically importing this class.
 *
 * <p>A <tt>TimeUnit</tt> is mainly used to inform blocking methods which
 * can timeout, how the timeout parameter should be interpreted. For example,
 * the following code will timeout in 50 milliseconds if the {@link Lock lock}
 * is not available:
 * <pre>  Lock lock = ...;
 *  if ( lock.tryLock(50L, TimeUnit.MILLISECONDS) ) ...
 * </pre>
 * while this code will timeout in 50 seconds:
 * <pre>  
 *  Lock lock = ...;
 *  if ( lock.tryLock(50L, TimeUnit.SECONDS) ) ...
 * </pre>
 * Note however, that there is no guarantee that a particular lock, in this
 * case, will be able to notice the passage of time at the same granularity
 * as the given <tt>TimeUnit</tt>.
 *
 * @since 1.5
 * @spec JSR-166
 * @revised $Date: 2003/03/29 02:17:05 $
 * @editor $Author: dholmes $
 *
 * @fixme The previous version created singleton subclass instances. I could
 * not see any reason to create subclasses instead of just instances.
 * Neither approach allows creation of your own units.
 */
public final class TimeUnit implements java.io.Serializable {

    /**
     * Return the current value of the system high resolution timer, in
     * nanoseconds. This method can only be used to measure elapsed time
     * and is not related to any notion of system, or wall-clock time.
     * Although the value returned represents nanoseconds since some
     * arbitrary start time in the past, the resolution at which this value
     * is updated is not specified. It provides have nanosecond precision, but
     * not necessarily nanosecond accuracy.
     * It is guaranteed that successive return
     * values from this method will not decrease.
     *
     * <p> For example to measure how long some code takes to execute, 
     * with nanosecond precision:
     * <pre>
     * long startTime = TimeUnit.nanoTime();
     * // ... the code being measured ...
     * long estimatedTime = TimeUnit.nanoTime() - startTime;
     * </pre>
     * 
     * @return The current value of the system high resolution timer, in
     * nanoseconds.
     *
     * @fixme Is this spec tight enough? Too tight? What about issues of
     * reading the TSC from different processors on a SMP?
     */
    public static final long nanoTime() {
        return JSR166Support.currentTimeNanos();
    }

    /**
     * Convert the given time duration in the given unit to the
     * current unit.  Conversions from finer to coarser granulaties
     * truncate, so lose precision. Conversions from coarser to finer
     * granularities may numerically overflow.
     *
     * @param duration the time duration in the given <tt>unit</tt>
     * @param unit the unit of the <tt>duration</tt> argument
     * @return the converted duration in the current unit.
     */
    public long convert(long duration, TimeUnit unit) {
        if (unit == this)
            return duration;
        if (index > unit.index) 
            return duration / multipliers[index - unit.index];
        else 
            return duration * multipliers[unit.index - index];
    }

    /**
     * Equivalent to <code>NANOOSECONDS.convert(duration, this)</code>.
     * @param duration the duration
     * @return the converted duration.
     **/
    public long toNanos(long duration) {
        if (index == NS)
            return duration;
        else
            return duration * multipliers[index];
    }
    
    /**
     * Perform a timed <tt>Object.wait</tt> using the current time unit. 
     * This is a convenience method that converts timeout arguments into the
     * form required by the <tt>Object.wait</tt> method.
     * <p>For example, you could implement a blocking <tt>poll</tt> method (see
     * {@link BlockingQueue#poll BlockingQueue.poll} using:
     * <pre>  public synchronized  Object poll(long timeout, TimeUnit unit) throws InterruptedException {
     *    while (empty) {
     *      unit.timedWait(this, timeout);
     *      ...
     *    }
     *  }</pre>
     * @param obj the object to wait on
     * @param timeout the maximum time to wait
     * @throws InterruptedException if interrupted while waiting.
     * @see Object#wait(long, int)
     */
    public void timedWait(Object obj, long timeout)
        throws InterruptedException {
        long ms = MILLISECONDS.convert(timeout, this);
        int ns = excessNanos(timeout, ms);
        obj.wait(ms, ns);
    }

    /**
     * Perform a timed <tt>Thread.join</tt> using the current time unit.
     * This is a convenience method that converts time arguments into the
     * form required by the <tt>Thread.join</tt> method.
     * @param thread the thread to wait for
     * @param timeout the maximum time to wait
     * @throws InterruptedException if interrupted while waiting.
     * @see Thread#join(long, int)
     */
    public void timedJoin(Thread thread, long timeout)
        throws InterruptedException {
        long ms = MILLISECONDS.convert(timeout, this);
        int ns = excessNanos(timeout, ms);
        thread.join(ms, ns);
    }
    
    /**
     * Perform a <tt>Thread.sleep</tt> using the current time unit.
     * This is a convenience method that converts time arguments into the
     * form required by the <tt>Thread.sleep</tt> method.
     * @param time the minimum time to sleep 
     * @throws InterruptedException if interrupted while sleeping.
     * @see Thread#sleep
     */
    public void sleep(long timeout) throws InterruptedException {
        long ms = MILLISECONDS.convert(timeout, this);
        int ns = excessNanos(timeout, ms);
        Thread.sleep(ms, ns);
    }

    /* ordered indices for each time unit */
    private static final int NS = 0;
    private static final int US = 1;
    private static final int MS = 2;
    private static final int S  = 3;

    /* quick lookup table for conversion factors */
    static final int[] multipliers = { 1, 1000, 1000*1000, 1000*1000*1000 };

    /* the index of this unit */
    int index;

    /** private constructor */
    TimeUnit(int index) { this.index = index; }

    /** 
     * Utility method to compute the excess-nanosecond argument to
     * wait, sleep, join.
     * @fixme overflow?
     */
    private int excessNanos(long time, long ms) {
        if (index == NS) 
            return (int) (time  - (ms * multipliers[MS-NS]));
        else if (index == US) 
            return (int) ((time * multipliers[US-NS]) - (ms * multipliers[MS-NS]));
        else 
            return 0;
    }

    /** Unit for one-second granularities */
    public static final TimeUnit SECONDS = new TimeUnit(S);

    /** Unit for one-millisecond granularities */
    public static final TimeUnit MILLISECONDS = new TimeUnit(MS);

    /** Unit for one-microsecond granularities */
    public static final TimeUnit MICROSECONDS = new TimeUnit(US);

    /** Unit for one-nanosecond granularities */
    public static final TimeUnit NANOSECONDS = new TimeUnit(NS);

}
Revision:	1.2
Committed:	Tue May 27 18:14:40 2003 UTC (21 years, 1 month ago) by dl
Branch:	MAIN
CVS Tags:	JSR166_PRELIMINARY_TEST_RELEASE_1, JSR166_PRERELEASE_0_1
Changes since 1.1:	+28 -13 lines
Log Message:	re-check-in initial implementations
#	User	Rev	Content
1	dl	1.2	/*
2			* Written by Doug Lea with assistance from members of JCP JSR-166
3			* Expert Group and released to the public domain. Use, modify, and
4			* redistribute this code in any way without acknowledgement.
5			*/
6
7	tim	1.1	package java.util.concurrent;
8
9			/**
10			* A <tt>TimeUnit</tt> represents time durations at a given unit of
11			* granularity and provides utility methods to convert across units,
12			* and to perform timing and delay operations in these units.
13			* <tt>TimeUnit</tt> is a "featherweight" class.
14			* It does not maintain time information, but only helps organize and
15			* use time representations that may be maintained separately across
16			* various contexts.
17	dl	1.2	* A static method {@link #nanoTime} provides access to a high
18	tim	1.1	* resolution, nanosecond, timer, which can be used to measure elapsed time.
19			*
20			* <p>The <tt>TimeUnit</tt> class cannot be directly instantiated.
21			* Use the {@link #SECONDS}, {@link #MILLISECONDS}, {@link #MICROSECONDS},
22			* and {@link #NANOSECONDS} static instances that provide predefined
23			* units of precision. If you use these frequently, consider
24			* statically importing this class.
25			*
26			* <p>A <tt>TimeUnit</tt> is mainly used to inform blocking methods which
27			* can timeout, how the timeout parameter should be interpreted. For example,
28			* the following code will timeout in 50 milliseconds if the {@link Lock lock}
29			* is not available:
30			* <pre> Lock lock = ...;
31			* if ( lock.tryLock(50L, TimeUnit.MILLISECONDS) ) ...
32			* </pre>
33			* while this code will timeout in 50 seconds:
34			* <pre>
35			* Lock lock = ...;
36			* if ( lock.tryLock(50L, TimeUnit.SECONDS) ) ...
37			* </pre>
38			* Note however, that there is no guarantee that a particular lock, in this
39			* case, will be able to notice the passage of time at the same granularity
40			* as the given <tt>TimeUnit</tt>.
41			*
42			* @since 1.5
43			* @spec JSR-166
44			* @revised $Date: 2003/03/29 02:17:05 $
45			* @editor $Author: dholmes $
46			*
47			* @fixme The previous version created singleton subclass instances. I could
48			* not see any reason to create subclasses instead of just instances.
49			* Neither approach allows creation of your own units.
50			*/
51			public final class TimeUnit implements java.io.Serializable {
52
53			/**
54			* Return the current value of the system high resolution timer, in
55			* nanoseconds. This method can only be used to measure elapsed time
56			* and is not related to any notion of system, or wall-clock time.
57			* Although the value returned represents nanoseconds since some
58			* arbitrary start time in the past, the resolution at which this value
59	dl	1.2	* is updated is not specified. It provides have nanosecond precision, but
60	tim	1.1	* not necessarily nanosecond accuracy.
61			* It is guaranteed that successive return
62			* values from this method will not decrease.
63			*
64			* <p> For example to measure how long some code takes to execute,
65			* with nanosecond precision:
66			* <pre>
67	dl	1.2	* long startTime = TimeUnit.nanoTime();
68	tim	1.1	* // ... the code being measured ...
69	dl	1.2	* long estimatedTime = TimeUnit.nanoTime() - startTime;
70	tim	1.1	* </pre>
71			*
72			* @return The current value of the system high resolution timer, in
73			* nanoseconds.
74			*
75			* @fixme Is this spec tight enough? Too tight? What about issues of
76			* reading the TSC from different processors on a SMP?
77			*/
78	dl	1.2	public static final long nanoTime() {
79			return JSR166Support.currentTimeNanos();
80	tim	1.1	}
81
82			/**
83			* Convert the given time duration in the given unit to the
84			* current unit. Conversions from finer to coarser granulaties
85			* truncate, so lose precision. Conversions from coarser to finer
86			* granularities may numerically overflow.
87			*
88			* @param duration the time duration in the given <tt>unit</tt>
89			* @param unit the unit of the <tt>duration</tt> argument
90			* @return the converted duration in the current unit.
91			*/
92			public long convert(long duration, TimeUnit unit) {
93	dl	1.2	if (unit == this)
94			return duration;
95			if (index > unit.index)
96	tim	1.1	return duration / multipliers[index - unit.index];
97	dl	1.2	else
98	tim	1.1	return duration * multipliers[unit.index - index];
99	dl	1.2	}
100
101			/**
102			* Equivalent to <code>NANOOSECONDS.convert(duration, this)</code>.
103			* @param duration the duration
104			* @return the converted duration.
105			**/
106			public long toNanos(long duration) {
107			if (index == NS)
108			return duration;
109			else
110			return duration * multipliers[index];
111	tim	1.1	}
112
113			/**
114			* Perform a timed <tt>Object.wait</tt> using the current time unit.
115			* This is a convenience method that converts timeout arguments into the
116			* form required by the <tt>Object.wait</tt> method.
117			* <p>For example, you could implement a blocking <tt>poll</tt> method (see
118			* {@link BlockingQueue#poll BlockingQueue.poll} using:
119			* <pre> public synchronized Object poll(long timeout, TimeUnit unit) throws InterruptedException {
120			* while (empty) {
121			* unit.timedWait(this, timeout);
122			* ...
123			* }
124			* }</pre>
125			* @param obj the object to wait on
126			* @param timeout the maximum time to wait
127			* @throws InterruptedException if interrupted while waiting.
128			* @see Object#wait(long, int)
129			*/
130			public void timedWait(Object obj, long timeout)
131			throws InterruptedException {
132			long ms = MILLISECONDS.convert(timeout, this);
133			int ns = excessNanos(timeout, ms);
134			obj.wait(ms, ns);
135			}
136
137			/**
138			* Perform a timed <tt>Thread.join</tt> using the current time unit.
139			* This is a convenience method that converts time arguments into the
140			* form required by the <tt>Thread.join</tt> method.
141			* @param thread the thread to wait for
142			* @param timeout the maximum time to wait
143			* @throws InterruptedException if interrupted while waiting.
144			* @see Thread#join(long, int)
145			*/
146			public void timedJoin(Thread thread, long timeout)
147			throws InterruptedException {
148			long ms = MILLISECONDS.convert(timeout, this);
149			int ns = excessNanos(timeout, ms);
150			thread.join(ms, ns);
151			}
152
153			/**
154			* Perform a <tt>Thread.sleep</tt> using the current time unit.
155			* This is a convenience method that converts time arguments into the
156			* form required by the <tt>Thread.sleep</tt> method.
157			* @param time the minimum time to sleep
158			* @throws InterruptedException if interrupted while sleeping.
159			* @see Thread#sleep
160			*/
161			public void sleep(long timeout) throws InterruptedException {
162			long ms = MILLISECONDS.convert(timeout, this);
163			int ns = excessNanos(timeout, ms);
164			Thread.sleep(ms, ns);
165			}
166
167			/* ordered indices for each time unit */
168			private static final int NS = 0;
169			private static final int US = 1;
170			private static final int MS = 2;
171			private static final int S = 3;
172
173			/* quick lookup table for conversion factors */
174			static final int[] multipliers = { 1, 1000, 10001000, 10001000*1000 };
175
176			/* the index of this unit */
177			int index;
178
179			/** private constructor */
180			TimeUnit(int index) { this.index = index; }
181
182			/**
183			* Utility method to compute the excess-nanosecond argument to
184			* wait, sleep, join.
185			* @fixme overflow?
186			*/
187			private int excessNanos(long time, long ms) {
188			if (index == NS)
189			return (int) (time - (ms * multipliers[MS-NS]));
190			else if (index == US)
191			return (int) ((time * multipliers[US-NS]) - (ms * multipliers[MS-NS]));
192			else
193			return 0;
194			}
195
196			/** Unit for one-second granularities */
197			public static final TimeUnit SECONDS = new TimeUnit(S);
198
199			/** Unit for one-millisecond granularities */
200			public static final TimeUnit MILLISECONDS = new TimeUnit(MS);
201
202			/** Unit for one-microsecond granularities */
203			public static final TimeUnit MICROSECONDS = new TimeUnit(US);
204
205			/** Unit for one-nanosecond granularities */
206			public static final TimeUnit NANOSECONDS = new TimeUnit(NS);
207
208			}