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java.lang.Object org.apache.openjpa.lib.util.concurrent.Utils
public final class Utils
This class groups together the functionality of java.util.concurrent that
cannot be fully and reliably implemented in backport, but for which some
form of emulation is possible.
Currently, this class contains methods related to nanosecond-precision
timing, particularly via the nanoTime()
method. To measure time
accurately, this method by default uses java.sun.Perf
on
JDK1.4.2 and it falls back to System.currentTimeMillis
on earlier JDKs.
Method Summary | |
---|---|
static long |
awaitNanos(Condition cond,
long nanosTimeout)
Causes the current thread to wait until it is signalled or interrupted, or the specified waiting time elapses. |
static Object[] |
collectionToArray(Collection c)
|
static Object[] |
collectionToArray(Collection c,
Object[] a)
|
static long |
nanoTime()
Returns the current value of the most precise available system timer, in nanoseconds. |
Methods inherited from class java.lang.Object |
---|
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait |
Method Detail |
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public static long nanoTime()
sun.misc.Perf
on Java 1.4.2, and falls back to
System.currentTimeMillis() emulation on earlier JDKs. Custom
timer can be provided via the system property
edu.emory.mathcs.backport.java.util.concurrent.NanoTimerProvider
.
The value of the property should name a class implementing
NanoTimer
interface.
Note: on JDK 1.4.2, sun.misc.Perf
timer seems to have
resolution of the order of 1 microsecond, measured on Linux.
public static long awaitNanos(Condition cond, long nanosTimeout) throws InterruptedException
Condition
interface, but it was moved to here since it
can only be emulated, with very little accuracy guarantees: the
efficient implementation requires accurate nanosecond timer and native
support for nanosecond-precision wait queues, which are not usually
present in JVMs prior to 1.5. Loss of precision may cause total waiting
times to be systematically shorter than specified when re-waits occur.
The lock associated with this condition is atomically
released and the current thread becomes disabled for thread scheduling
purposes and lies dormant until one of five things happens:
edu.emory.mathcs.backport.java.util.concurrent.locks.Condition#signal
method for this
Condition and the current thread happens to be chosen as the
thread to be awakened; or
edu.emory.mathcs.backport.java.util.concurrent.locks.Condition#signalAll
method for this
Condition; or
interrupts
the current
thread, and interruption of thread suspension is supported; or
interrupted
while waiting
and interruption of thread suspension is supported,
InterruptedException
is thrown and the current thread's
interrupted status is cleared. It is not specified, in the first
case, whether or not the test for interruption occurs before the lock
is released. The method returns an estimate of the number of nanoseconds
remaining to wait given the supplied nanosTimeout
value upon return, or a value less than or equal to zero if it
timed out. Accuracy of this estimate is directly dependent on the
accuracy of nanoTime()
. This value can be used to determine
whether and how long to re-wait in cases where the wait returns but an
awaited condition still does not hold. Typical uses of this method take
the following form:
synchronized boolean aMethod(long timeout, TimeUnit unit) { long nanosTimeout = unit.toNanos(timeout); while (!conditionBeingWaitedFor) { if (nanosTimeout > 0) nanosTimeout = theCondition.awaitNanos(nanosTimeout); else return false; } // ... }Implementation Considerations The current thread is assumed to hold the lock associated with this Condition when this method is called. It is up to the implementation to determine if this is the case and if not, how to respond. Typically, an exception will be thrown(such as
IllegalMonitorStateException
) and the
implementation must document that fact.
A condition implementation can favor responding to an interrupt over
normal method return in response to a signal, or over indicating the
elapse of the specified waiting time. In either case the implementation
must ensure that the signal is redirected to another waiting thread, if
there is one.
cond
- the condition to wait fornanosTimeout
- the maximum time to wait, in nanoseconds
InterruptedException
- if the current thread is interrupted(and
interruption of thread suspension is supported).public static Object[] collectionToArray(Collection c)
public static Object[] collectionToArray(Collection c, Object[] a)
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