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<div class="subTitle"><span class="packageLabelInType">Package</span> <a href="../../../../../org/apache/commons/lang3/concurrent/package-summary.html">org.apache.commons.lang3.concurrent</a></div>
<h2 title="Class TimedSemaphore" class="title">Class TimedSemaphore</h2>
</div>
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<ul class="inheritance">
<li><a href="https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true" title="class or interface in java.lang" class="externalLink">java.lang.Object</a></li>
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<li>org.apache.commons.lang3.concurrent.TimedSemaphore</li>
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<pre>public class <span class="typeNameLabel">TimedSemaphore</span>
extends <a href="https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true" title="class or interface in java.lang" class="externalLink">Object</a></pre>
<div class="block"><p>
A specialized <em>semaphore</em> implementation that provides a number of
permits in a given time frame.
</p>
<p>
This class is similar to the <code>java.util.concurrent.Semaphore</code> class
provided by the JDK in that it manages a configurable number of permits.
Using the <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#acquire--"><code>acquire()</code></a> method a permit can be requested by a thread.
However, there is an additional timing dimension: there is no <code>
release()</code> method for freeing a permit, but all permits are automatically
released at the end of a configurable time frame. If a thread calls
<a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#acquire--"><code>acquire()</code></a> and the available permits are already exhausted for this
time frame, the thread is blocked. When the time frame ends all permits
requested so far are restored, and blocking threads are waked up again, so
that they can try to acquire a new permit. This basically means that in the
specified time frame only the given number of operations is possible.
</p>
<p>
A use case for this class is to artificially limit the load produced by a
process. As an example consider an application that issues database queries
on a production system in a background process to gather statistical
information. This background processing should not produce so much database
load that the functionality and the performance of the production system are
impacted. Here a <code>TimedSemaphore</code> could be installed to guarantee that
only a given number of database queries are issued per second.
</p>
<p>
A thread class for performing database queries could look as follows:
</p>
<pre>
public class StatisticsThread extends Thread {
// The semaphore for limiting database load.
private final TimedSemaphore semaphore;
// Create an instance and set the semaphore
public StatisticsThread(TimedSemaphore timedSemaphore) {
semaphore = timedSemaphore;
}
// Gather statistics
public void run() {
try {
while(true) {
semaphore.acquire(); // limit database load
performQuery(); // issue a query
}
} catch(InterruptedException) {
// fall through
}
}
...
}
</pre>
<p>
The following code fragment shows how a <code>TimedSemaphore</code> is created
that allows only 10 operations per second and passed to the statistics
thread:
</p>
<pre>
TimedSemaphore sem = new TimedSemaphore(1, TimeUnit.SECOND, 10);
StatisticsThread thread = new StatisticsThread(sem);
thread.start();
</pre>
<p>
When creating an instance the time period for the semaphore must be
specified. <code>TimedSemaphore</code> uses an executor service with a
corresponding period to monitor this interval. The <code>
ScheduledExecutorService</code> to be used for this purpose can be provided at
construction time. Alternatively the class creates an internal executor
service.
</p>
<p>
Client code that uses <code>TimedSemaphore</code> has to call the
<a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#acquire--"><code>acquire()</code></a> method in each processing step. <code>TimedSemaphore</code>
keeps track of the number of invocations of the <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#acquire--"><code>acquire()</code></a> method and
blocks the calling thread if the counter exceeds the limit specified. When
the timer signals the end of the time period the counter is reset and all
waiting threads are released. Then another cycle can start.
</p>
<p>
An alternative to <code>acquire()</code> is the <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#tryAcquire--"><code>tryAcquire()</code></a> method. This
method checks whether the semaphore is under the specified limit and
increases the internal counter if this is the case. The return value is then
<strong>true</strong>, and the calling thread can continue with its action.
If the semaphore is already at its limit, <code>tryAcquire()</code> immediately
returns <strong>false</strong> without blocking; the calling thread must
then abort its action. This usage scenario prevents blocking of threads.
</p>
<p>
It is possible to modify the limit at any time using the
<a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#setLimit-int-"><code>setLimit(int)</code></a> method. This is useful if the load produced by an
operation has to be adapted dynamically. In the example scenario with the
thread collecting statistics it may make sense to specify a low limit during
day time while allowing a higher load in the night time. Reducing the limit
takes effect immediately by blocking incoming callers. If the limit is
increased, waiting threads are not released immediately, but wake up when the
timer runs out. Then, in the next period more processing steps can be
performed without blocking. By setting the limit to 0 the semaphore can be
switched off: in this mode the <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#acquire--"><code>acquire()</code></a> method never blocks, but
lets all callers pass directly.
</p>
<p>
When the <code>TimedSemaphore</code> is no more needed its <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#shutdown--"><code>shutdown()</code></a>
method should be called. This causes the periodic task that monitors the time
interval to be canceled. If the <code>ScheduledExecutorService</code> has been
created by the semaphore at construction time, it is also shut down.
resources. After that <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#acquire--"><code>acquire()</code></a> must not be called any more.
</p></div>
<dl>
<dt><span class="simpleTagLabel">Since:</span></dt>
<dd>3.0</dd>
</dl>
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<th class="colFirst" scope="col">Modifier and Type</th>
<th class="colSecond" scope="col">Field</th>
<th class="colLast" scope="col">Description</th>
</tr>
<tr class="altColor">
<td class="colFirst"><code>static int</code></td>
<th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#NO_LIMIT">NO_LIMIT</a></span></code></th>
<td class="colLast">
<div class="block">Constant for a value representing no limit.</div>
</td>
</tr>
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<tr>
<th class="colFirst" scope="col">Constructor</th>
<th class="colLast" scope="col">Description</th>
</tr>
<tr class="altColor">
<th class="colConstructorName" scope="row"><code><span class="memberNameLink"><a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#TimedSemaphore-long-java.util.concurrent.TimeUnit-int-">TimedSemaphore</a></span>​(long timePeriod,
<a href="https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/TimeUnit.html?is-external=true" title="class or interface in java.util.concurrent" class="externalLink">TimeUnit</a> timeUnit,
int limit)</code></th>
<td class="colLast">
<div class="block">Creates a new instance of <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html" title="class in org.apache.commons.lang3.concurrent"><code>TimedSemaphore</code></a> and initializes it with
the given time period and the limit.</div>
</td>
</tr>
<tr class="rowColor">
<th class="colConstructorName" scope="row"><code><span class="memberNameLink"><a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#TimedSemaphore-java.util.concurrent.ScheduledExecutorService-long-java.util.concurrent.TimeUnit-int-">TimedSemaphore</a></span>​(<a href="https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ScheduledExecutorService.html?is-external=true" title="class or interface in java.util.concurrent" class="externalLink">ScheduledExecutorService</a> service,
long timePeriod,
<a href="https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/TimeUnit.html?is-external=true" title="class or interface in java.util.concurrent" class="externalLink">TimeUnit</a> timeUnit,
int limit)</code></th>
<td class="colLast">
<div class="block">Creates a new instance of <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html" title="class in org.apache.commons.lang3.concurrent"><code>TimedSemaphore</code></a> and initializes it with
an executor service, the given time period, and the limit.</div>
</td>
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<h3>Method Summary</h3>
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<caption><span id="t0" class="activeTableTab"><span>All Methods</span><span class="tabEnd"> </span></span><span id="t2" class="tableTab"><span><a href="javascript:show(2);">Instance Methods</a></span><span class="tabEnd"> </span></span><span id="t4" class="tableTab"><span><a href="javascript:show(8);">Concrete Methods</a></span><span class="tabEnd"> </span></span></caption>
<tr>
<th class="colFirst" scope="col">Modifier and Type</th>
<th class="colSecond" scope="col">Method</th>
<th class="colLast" scope="col">Description</th>
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<tr id="i0" class="altColor">
<td class="colFirst"><code>void</code></td>
<th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#acquire--">acquire</a></span>()</code></th>
<td class="colLast">
<div class="block">Acquires a permit from this semaphore.</div>
</td>
</tr>
<tr id="i1" class="rowColor">
<td class="colFirst"><code>int</code></td>
<th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#getAcquireCount--">getAcquireCount</a></span>()</code></th>
<td class="colLast">
<div class="block">Returns the number of invocations of the <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#acquire--"><code>acquire()</code></a> method for
the current period.</div>
</td>
</tr>
<tr id="i2" class="altColor">
<td class="colFirst"><code>int</code></td>
<th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#getAvailablePermits--">getAvailablePermits</a></span>()</code></th>
<td class="colLast">
<div class="block">Returns the number of calls to the <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#acquire--"><code>acquire()</code></a> method that can
still be performed in the current period without blocking.</div>
</td>
</tr>
<tr id="i3" class="rowColor">
<td class="colFirst"><code>double</code></td>
<th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#getAverageCallsPerPeriod--">getAverageCallsPerPeriod</a></span>()</code></th>
<td class="colLast">
<div class="block">Returns the average number of successful (i.e.</div>
</td>
</tr>
<tr id="i4" class="altColor">
<td class="colFirst"><code>protected <a href="https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ScheduledExecutorService.html?is-external=true" title="class or interface in java.util.concurrent" class="externalLink">ScheduledExecutorService</a></code></td>
<th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#getExecutorService--">getExecutorService</a></span>()</code></th>
<td class="colLast">
<div class="block">Returns the executor service used by this instance.</div>
</td>
</tr>
<tr id="i5" class="rowColor">
<td class="colFirst"><code>int</code></td>
<th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#getLastAcquiresPerPeriod--">getLastAcquiresPerPeriod</a></span>()</code></th>
<td class="colLast">
<div class="block">Returns the number of (successful) acquire invocations during the last
period.</div>
</td>
</tr>
<tr id="i6" class="altColor">
<td class="colFirst"><code>int</code></td>
<th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#getLimit--">getLimit</a></span>()</code></th>
<td class="colLast">
<div class="block">Returns the limit enforced by this semaphore.</div>
</td>
</tr>
<tr id="i7" class="rowColor">
<td class="colFirst"><code>long</code></td>
<th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#getPeriod--">getPeriod</a></span>()</code></th>
<td class="colLast">
<div class="block">Returns the time period.</div>
</td>
</tr>
<tr id="i8" class="altColor">
<td class="colFirst"><code><a href="https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/TimeUnit.html?is-external=true" title="class or interface in java.util.concurrent" class="externalLink">TimeUnit</a></code></td>
<th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#getUnit--">getUnit</a></span>()</code></th>
<td class="colLast">
<div class="block">Returns the time unit.</div>
</td>
</tr>
<tr id="i9" class="rowColor">
<td class="colFirst"><code>boolean</code></td>
<th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#isShutdown--">isShutdown</a></span>()</code></th>
<td class="colLast">
<div class="block">Tests whether the <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#shutdown--"><code>shutdown()</code></a> method has been called on this
object.</div>
</td>
</tr>
<tr id="i10" class="altColor">
<td class="colFirst"><code>void</code></td>
<th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#setLimit-int-">setLimit</a></span>​(int limit)</code></th>
<td class="colLast">
<div class="block">Sets the limit.</div>
</td>
</tr>
<tr id="i11" class="rowColor">
<td class="colFirst"><code>void</code></td>
<th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#shutdown--">shutdown</a></span>()</code></th>
<td class="colLast">
<div class="block">Initializes a shutdown.</div>
</td>
</tr>
<tr id="i12" class="altColor">
<td class="colFirst"><code>protected <a href="https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ScheduledFuture.html?is-external=true" title="class or interface in java.util.concurrent" class="externalLink">ScheduledFuture</a><?></code></td>
<th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#startTimer--">startTimer</a></span>()</code></th>
<td class="colLast">
<div class="block">Starts the timer.</div>
</td>
</tr>
<tr id="i13" class="rowColor">
<td class="colFirst"><code>boolean</code></td>
<th class="colSecond" scope="row"><code><span class="memberNameLink"><a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#tryAcquire--">tryAcquire</a></span>()</code></th>
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<div class="block">Tries to acquire a permit from this semaphore.</div>
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<h3>Methods inherited from class java.lang.<a href="https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true" title="class or interface in java.lang" class="externalLink">Object</a></h3>
<code><a href="https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#clone--" title="class or interface in java.lang" class="externalLink">clone</a>, <a href="https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#equals-java.lang.Object-" title="class or interface in java.lang" class="externalLink">equals</a>, <a href="https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#finalize--" title="class or interface in java.lang" class="externalLink">finalize</a>, <a href="https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#getClass--" title="class or interface in java.lang" class="externalLink">getClass</a>, <a href="https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#hashCode--" title="class or interface in java.lang" class="externalLink">hashCode</a>, <a href="https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#notify--" title="class or interface in java.lang" class="externalLink">notify</a>, <a href="https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#notifyAll--" title="class or interface in java.lang" class="externalLink">notifyAll</a>, <a href="https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#toString--" title="class or interface in java.lang" class="externalLink">toString</a>, <a href="https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#wait--" title="class or interface in java.lang" class="externalLink">wait</a>, <a href="https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#wait-long-" title="class or interface in java.lang" class="externalLink">wait</a>, <a href="https://docs.oracle.com/javase/7/docs/api/java/lang/Object.html?is-external=true#wait-long-int-" title="class or interface in java.lang" class="externalLink">wait</a></code></li>
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<h4>NO_LIMIT</h4>
<pre>public static final int NO_LIMIT</pre>
<div class="block">Constant for a value representing no limit. If the limit is set to a
value less or equal this constant, the <code>TimedSemaphore</code> will be
effectively switched off.</div>
<dl>
<dt><span class="seeLabel">See Also:</span></dt>
<dd><a href="../../../../../constant-values.html#org.apache.commons.lang3.concurrent.TimedSemaphore.NO_LIMIT">Constant Field Values</a></dd>
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<pre>public TimedSemaphore​(long timePeriod,
<a href="https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/TimeUnit.html?is-external=true" title="class or interface in java.util.concurrent" class="externalLink">TimeUnit</a> timeUnit,
int limit)</pre>
<div class="block">Creates a new instance of <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html" title="class in org.apache.commons.lang3.concurrent"><code>TimedSemaphore</code></a> and initializes it with
the given time period and the limit.</div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>timePeriod</code> - the time period</dd>
<dd><code>timeUnit</code> - the unit for the period</dd>
<dd><code>limit</code> - the limit for the semaphore</dd>
<dt><span class="throwsLabel">Throws:</span></dt>
<dd><code><a href="https://docs.oracle.com/javase/7/docs/api/java/lang/IllegalArgumentException.html?is-external=true" title="class or interface in java.lang" class="externalLink">IllegalArgumentException</a></code> - if the period is less or equals 0</dd>
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<pre>public TimedSemaphore​(<a href="https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ScheduledExecutorService.html?is-external=true" title="class or interface in java.util.concurrent" class="externalLink">ScheduledExecutorService</a> service,
long timePeriod,
<a href="https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/TimeUnit.html?is-external=true" title="class or interface in java.util.concurrent" class="externalLink">TimeUnit</a> timeUnit,
int limit)</pre>
<div class="block">Creates a new instance of <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html" title="class in org.apache.commons.lang3.concurrent"><code>TimedSemaphore</code></a> and initializes it with
an executor service, the given time period, and the limit. The executor
service will be used for creating a periodic task for monitoring the time
period. It can be <b>null</b>, then a default service will be created.</div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>service</code> - the executor service</dd>
<dd><code>timePeriod</code> - the time period</dd>
<dd><code>timeUnit</code> - the unit for the period</dd>
<dd><code>limit</code> - the limit for the semaphore</dd>
<dt><span class="throwsLabel">Throws:</span></dt>
<dd><code><a href="https://docs.oracle.com/javase/7/docs/api/java/lang/IllegalArgumentException.html?is-external=true" title="class or interface in java.lang" class="externalLink">IllegalArgumentException</a></code> - if the period is less or equals 0</dd>
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<pre>public final int getLimit()</pre>
<div class="block">Returns the limit enforced by this semaphore. The limit determines how
many invocations of <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#acquire--"><code>acquire()</code></a> are allowed within the monitored
period.</div>
<dl>
<dt><span class="returnLabel">Returns:</span></dt>
<dd>the limit</dd>
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<pre>public final void setLimit​(int limit)</pre>
<div class="block">Sets the limit. This is the number of times the <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#acquire--"><code>acquire()</code></a> method
can be called within the time period specified. If this limit is reached,
further invocations of <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#acquire--"><code>acquire()</code></a> will block. Setting the limit
to a value <= <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#NO_LIMIT"><code>NO_LIMIT</code></a> will cause the limit to be disabled,
i.e. an arbitrary number of<a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#acquire--"><code>acquire()</code></a> invocations is allowed in
the time period.</div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>limit</code> - the limit</dd>
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<pre>public void shutdown()</pre>
<div class="block">Initializes a shutdown. After that the object cannot be used any more.
This method can be invoked an arbitrary number of times. All invocations
after the first one do not have any effect.</div>
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<pre>public boolean isShutdown()</pre>
<div class="block">Tests whether the <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#shutdown--"><code>shutdown()</code></a> method has been called on this
object. If this method returns <b>true</b>, this instance cannot be used
any longer.</div>
<dl>
<dt><span class="returnLabel">Returns:</span></dt>
<dd>a flag whether a shutdown has been performed</dd>
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<pre>public void acquire()
throws <a href="https://docs.oracle.com/javase/7/docs/api/java/lang/InterruptedException.html?is-external=true" title="class or interface in java.lang" class="externalLink">InterruptedException</a></pre>
<div class="block">Acquires a permit from this semaphore. This method will block if
the limit for the current period has already been reached. If
<a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#shutdown--"><code>shutdown()</code></a> has already been invoked, calling this method will
cause an exception. The very first call of this method starts the timer
task which monitors the time period set for this <code>TimedSemaphore</code>.
From now on the semaphore is active.</div>
<dl>
<dt><span class="throwsLabel">Throws:</span></dt>
<dd><code><a href="https://docs.oracle.com/javase/7/docs/api/java/lang/InterruptedException.html?is-external=true" title="class or interface in java.lang" class="externalLink">InterruptedException</a></code> - if the thread gets interrupted</dd>
<dd><code><a href="https://docs.oracle.com/javase/7/docs/api/java/lang/IllegalStateException.html?is-external=true" title="class or interface in java.lang" class="externalLink">IllegalStateException</a></code> - if this semaphore is already shut down</dd>
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<pre>public boolean tryAcquire()</pre>
<div class="block">Tries to acquire a permit from this semaphore. If the limit of this semaphore has
not yet been reached, a permit is acquired, and this method returns
<strong>true</strong>. Otherwise, this method returns immediately with the result
<strong>false</strong>.</div>
<dl>
<dt><span class="returnLabel">Returns:</span></dt>
<dd><strong>true</strong> if a permit could be acquired; <strong>false</strong>
otherwise</dd>
<dt><span class="throwsLabel">Throws:</span></dt>
<dd><code><a href="https://docs.oracle.com/javase/7/docs/api/java/lang/IllegalStateException.html?is-external=true" title="class or interface in java.lang" class="externalLink">IllegalStateException</a></code> - if this semaphore is already shut down</dd>
<dt><span class="simpleTagLabel">Since:</span></dt>
<dd>3.5</dd>
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<pre>public int getLastAcquiresPerPeriod()</pre>
<div class="block">Returns the number of (successful) acquire invocations during the last
period. This is the number of times the <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#acquire--"><code>acquire()</code></a> method was
called without blocking. This can be useful for testing or debugging
purposes or to determine a meaningful threshold value. If a limit is set,
the value returned by this method won't be greater than this limit.</div>
<dl>
<dt><span class="returnLabel">Returns:</span></dt>
<dd>the number of non-blocking invocations of the <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#acquire--"><code>acquire()</code></a>
method</dd>
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<pre>public int getAcquireCount()</pre>
<div class="block">Returns the number of invocations of the <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#acquire--"><code>acquire()</code></a> method for
the current period. This may be useful for testing or debugging purposes.</div>
<dl>
<dt><span class="returnLabel">Returns:</span></dt>
<dd>the current number of <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#acquire--"><code>acquire()</code></a> invocations</dd>
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<pre>public int getAvailablePermits()</pre>
<div class="block">Returns the number of calls to the <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#acquire--"><code>acquire()</code></a> method that can
still be performed in the current period without blocking. This method
can give an indication whether it is safe to call the <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#acquire--"><code>acquire()</code></a>
method without risking to be suspended. However, there is no guarantee
that a subsequent call to <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#acquire--"><code>acquire()</code></a> actually is not-blocking
because in the mean time other threads may have invoked the semaphore.</div>
<dl>
<dt><span class="returnLabel">Returns:</span></dt>
<dd>the current number of available <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#acquire--"><code>acquire()</code></a> calls in the
current period</dd>
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<pre>public double getAverageCallsPerPeriod()</pre>
<div class="block">Returns the average number of successful (i.e. non-blocking)
<a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#acquire--"><code>acquire()</code></a> invocations for the entire life-time of this <code>
TimedSemaphore</code>. This method can be used for instance for statistical
calculations.</div>
<dl>
<dt><span class="returnLabel">Returns:</span></dt>
<dd>the average number of <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#acquire--"><code>acquire()</code></a> invocations per time
unit</dd>
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<pre>public long getPeriod()</pre>
<div class="block">Returns the time period. This is the time monitored by this semaphore.
Only a given number of invocations of the <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#acquire--"><code>acquire()</code></a> method is
possible in this period.</div>
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<dt><span class="returnLabel">Returns:</span></dt>
<dd>the time period</dd>
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<pre>public <a href="https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/TimeUnit.html?is-external=true" title="class or interface in java.util.concurrent" class="externalLink">TimeUnit</a> getUnit()</pre>
<div class="block">Returns the time unit. This is the unit used by <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#getPeriod--"><code>getPeriod()</code></a>.</div>
<dl>
<dt><span class="returnLabel">Returns:</span></dt>
<dd>the time unit</dd>
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<pre>protected <a href="https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ScheduledExecutorService.html?is-external=true" title="class or interface in java.util.concurrent" class="externalLink">ScheduledExecutorService</a> getExecutorService()</pre>
<div class="block">Returns the executor service used by this instance.</div>
<dl>
<dt><span class="returnLabel">Returns:</span></dt>
<dd>the executor service</dd>
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<h4>startTimer</h4>
<pre>protected <a href="https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/ScheduledFuture.html?is-external=true" title="class or interface in java.util.concurrent" class="externalLink">ScheduledFuture</a><?> startTimer()</pre>
<div class="block">Starts the timer. This method is called when <a href="../../../../../org/apache/commons/lang3/concurrent/TimedSemaphore.html#acquire--"><code>acquire()</code></a> is called
for the first time. It schedules a task to be executed at fixed rate to
monitor the time period specified.</div>
<dl>
<dt><span class="returnLabel">Returns:</span></dt>
<dd>a future object representing the task scheduled</dd>
</dl>
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