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: 2003/05/27 18:14:40 $
 * @editor $Author: dl $
 *
 */
public final class TimeUnit implements java.io.Serializable {

    /**
     * Return the current value of the system high resolution timer, in
     * nanoseconds. 
     * <p>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 nanosecond precision, but
     * not necessarily nanosecond accuracy.
     * <p>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>NANOSECONDS.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:	1.3
Committed:	Mon Jun 9 23:42:27 2003 UTC (21 years ago) by dholmes
Branch:	MAIN
Changes since 1.2:	+11 -13 lines
Log Message:	Removed fixme. Fixed minor typos and layout issues.
#	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	dholmes	1.3	* @revised $Date: 2003/05/27 18:14:40 $
45			* @editor $Author: dl $
46	tim	1.1	*
47			*/
48			public final class TimeUnit implements java.io.Serializable {
49
50			/**
51			* Return the current value of the system high resolution timer, in
52	dholmes	1.3	* nanoseconds.
53			* <p>This method can only be used to measure elapsed time
54	tim	1.1	* and is not related to any notion of system, or wall-clock time.
55			* Although the value returned represents nanoseconds since some
56			* arbitrary start time in the past, the resolution at which this value
57	dholmes	1.3	* is updated is not specified. It provides nanosecond precision, but
58	tim	1.1	* not necessarily nanosecond accuracy.
59	dholmes	1.3	* <p>It is guaranteed that successive return
60	tim	1.1	* values from this method will not decrease.
61			*
62	dholmes	1.3	* <p> For example, to measure how long some code takes to execute,
63	tim	1.1	* with nanosecond precision:
64			* <pre>
65	dholmes	1.3	* long startTime = TimeUnit.nanoTime();
66			* // ... the code being measured ...
67			* long estimatedTime = TimeUnit.nanoTime() - startTime;
68	tim	1.1	* </pre>
69			*
70			* @return The current value of the system high resolution timer, in
71			* nanoseconds.
72			*
73			* @fixme Is this spec tight enough? Too tight? What about issues of
74			* reading the TSC from different processors on a SMP?
75			*/
76	dl	1.2	public static final long nanoTime() {
77			return JSR166Support.currentTimeNanos();
78	tim	1.1	}
79
80			/**
81			* Convert the given time duration in the given unit to the
82			* current unit. Conversions from finer to coarser granulaties
83			* truncate, so lose precision. Conversions from coarser to finer
84			* granularities may numerically overflow.
85			*
86			* @param duration the time duration in the given <tt>unit</tt>
87			* @param unit the unit of the <tt>duration</tt> argument
88			* @return the converted duration in the current unit.
89			*/
90			public long convert(long duration, TimeUnit unit) {
91	dl	1.2	if (unit == this)
92			return duration;
93			if (index > unit.index)
94	tim	1.1	return duration / multipliers[index - unit.index];
95	dl	1.2	else
96	tim	1.1	return duration * multipliers[unit.index - index];
97	dl	1.2	}
98
99			/**
100	dholmes	1.3	* Equivalent to <code>NANOSECONDS.convert(duration, this)</code>.
101	dl	1.2	* @param duration the duration
102			* @return the converted duration.
103			**/
104			public long toNanos(long duration) {
105			if (index == NS)
106			return duration;
107			else
108			return duration * multipliers[index];
109	tim	1.1	}
110
111			/**
112			* Perform a timed <tt>Object.wait</tt> using the current time unit.
113			* This is a convenience method that converts timeout arguments into the
114			* form required by the <tt>Object.wait</tt> method.
115			* <p>For example, you could implement a blocking <tt>poll</tt> method (see
116			* {@link BlockingQueue#poll BlockingQueue.poll} using:
117			* <pre> public synchronized Object poll(long timeout, TimeUnit unit) throws InterruptedException {
118			* while (empty) {
119			* unit.timedWait(this, timeout);
120			* ...
121			* }
122			* }</pre>
123			* @param obj the object to wait on
124			* @param timeout the maximum time to wait
125			* @throws InterruptedException if interrupted while waiting.
126			* @see Object#wait(long, int)
127			*/
128			public void timedWait(Object obj, long timeout)
129			throws InterruptedException {
130			long ms = MILLISECONDS.convert(timeout, this);
131			int ns = excessNanos(timeout, ms);
132			obj.wait(ms, ns);
133			}
134
135			/**
136			* Perform a timed <tt>Thread.join</tt> using the current time unit.
137			* This is a convenience method that converts time arguments into the
138			* form required by the <tt>Thread.join</tt> method.
139			* @param thread the thread to wait for
140			* @param timeout the maximum time to wait
141			* @throws InterruptedException if interrupted while waiting.
142			* @see Thread#join(long, int)
143			*/
144			public void timedJoin(Thread thread, long timeout)
145			throws InterruptedException {
146			long ms = MILLISECONDS.convert(timeout, this);
147			int ns = excessNanos(timeout, ms);
148			thread.join(ms, ns);
149			}
150
151			/**
152			* Perform a <tt>Thread.sleep</tt> using the current time unit.
153			* This is a convenience method that converts time arguments into the
154			* form required by the <tt>Thread.sleep</tt> method.
155			* @param time the minimum time to sleep
156			* @throws InterruptedException if interrupted while sleeping.
157			* @see Thread#sleep
158			*/
159			public void sleep(long timeout) throws InterruptedException {
160			long ms = MILLISECONDS.convert(timeout, this);
161			int ns = excessNanos(timeout, ms);
162			Thread.sleep(ms, ns);
163			}
164
165			/* ordered indices for each time unit */
166			private static final int NS = 0;
167			private static final int US = 1;
168			private static final int MS = 2;
169			private static final int S = 3;
170
171			/* quick lookup table for conversion factors */
172			static final int[] multipliers = { 1, 1000, 10001000, 10001000*1000 };
173
174			/* the index of this unit */
175			int index;
176
177			/** private constructor */
178			TimeUnit(int index) { this.index = index; }
179
180			/**
181			* Utility method to compute the excess-nanosecond argument to
182			* wait, sleep, join.
183			* @fixme overflow?
184			*/
185			private int excessNanos(long time, long ms) {
186			if (index == NS)
187			return (int) (time - (ms * multipliers[MS-NS]));
188			else if (index == US)
189			return (int) ((time * multipliers[US-NS]) - (ms * multipliers[MS-NS]));
190			else
191			return 0;
192			}
193
194			/** Unit for one-second granularities */
195			public static final TimeUnit SECONDS = new TimeUnit(S);
196
197			/** Unit for one-millisecond granularities */
198			public static final TimeUnit MILLISECONDS = new TimeUnit(MS);
199
200			/** Unit for one-microsecond granularities */
201			public static final TimeUnit MICROSECONDS = new TimeUnit(US);
202
203			/** Unit for one-nanosecond granularities */
204			public static final TimeUnit NANOSECONDS = new TimeUnit(NS);
205
206			}