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 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
#	Content
1	/*
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	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	* A static method {@link #nanoTime} provides access to a high
18	* 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	* is updated is not specified. It provides have nanosecond precision, but
60	* 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	* long startTime = TimeUnit.nanoTime();
68	* // ... the code being measured ...
69	* long estimatedTime = TimeUnit.nanoTime() - startTime;
70	* </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	public static final long nanoTime() {
79	return JSR166Support.currentTimeNanos();
80	}
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	if (unit == this)
94	return duration;
95	if (index > unit.index)
96	return duration / multipliers[index - unit.index];
97	else
98	return duration * multipliers[unit.index - index];
99	}
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	}
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	}