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<div class="subTitle">org.apache.ignite.compute</div>
<h2 title="Interface ComputeTask" class="title">Interface ComputeTask&lt;T,R&gt;</h2>
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<dt><span class="paramLabel">Type Parameters:</span></dt>
<dd><code>T</code> - Type of the task argument that is passed into <a href="../../../../org/apache/ignite/compute/ComputeTask.html#map-java.util.List-T-"><code>map(List, Object)</code></a> method.</dd>
<dd><code>R</code> - Type of the task result returning from <a href="../../../../org/apache/ignite/compute/ComputeTask.html#reduce-java.util.List-"><code>reduce(List)</code></a> method.</dd>
</dl>
<dl>
<dt>All Superinterfaces:</dt>
<dd><a href="http://docs.oracle.com/javase/8/docs/api/java/io/Serializable.html?is-external=true" title="class or interface in java.io">Serializable</a></dd>
</dl>
<dl>
<dt>All Known Implementing Classes:</dt>
<dd><a href="../../../../org/apache/ignite/compute/ComputeTaskAdapter.html" title="class in org.apache.ignite.compute">ComputeTaskAdapter</a>, <a href="../../../../org/apache/ignite/compute/ComputeTaskSplitAdapter.html" title="class in org.apache.ignite.compute">ComputeTaskSplitAdapter</a>, <a href="../../../../org/apache/ignite/ml/genetic/CrossOverTask.html" title="class in org.apache.ignite.ml.genetic">CrossOverTask</a>, <a href="../../../../org/apache/ignite/ml/genetic/FitnessTask.html" title="class in org.apache.ignite.ml.genetic">FitnessTask</a>, <a href="../../../../org/apache/ignite/compute/gridify/aop/GridifyDefaultRangeTask.html" title="class in org.apache.ignite.compute.gridify.aop">GridifyDefaultRangeTask</a>, <a href="../../../../org/apache/ignite/compute/gridify/aop/GridifyDefaultTask.html" title="class in org.apache.ignite.compute.gridify.aop">GridifyDefaultTask</a>, <a href="../../../../org/apache/ignite/compute/gridify/GridifyTaskAdapter.html" title="class in org.apache.ignite.compute.gridify">GridifyTaskAdapter</a>, <a href="../../../../org/apache/ignite/compute/gridify/GridifyTaskSplitAdapter.html" title="class in org.apache.ignite.compute.gridify">GridifyTaskSplitAdapter</a>, <a href="../../../../org/apache/ignite/igfs/mapreduce/IgfsTask.html" title="class in org.apache.ignite.igfs.mapreduce">IgfsTask</a>, <a href="../../../../org/apache/ignite/igfs/mapreduce/IgfsTaskNoReduceAdapter.html" title="class in org.apache.ignite.igfs.mapreduce">IgfsTaskNoReduceAdapter</a>, <a href="../../../../org/apache/ignite/ml/genetic/MutateTask.html" title="class in org.apache.ignite.ml.genetic">MutateTask</a>, <a href="../../../../org/apache/ignite/ml/genetic/TruncateSelectionTask.html" title="class in org.apache.ignite.ml.genetic">TruncateSelectionTask</a></dd>
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<pre>public interface <span class="typeNameLabel">ComputeTask&lt;T,R&gt;</span>
extends <a href="http://docs.oracle.com/javase/8/docs/api/java/io/Serializable.html?is-external=true" title="class or interface in java.io">Serializable</a></pre>
<div class="block">Grid task interface defines a task that can be executed on the grid. Grid task
is responsible for splitting business logic into multiple grid jobs, receiving
results from individual grid jobs executing on remote nodes, and reducing
(aggregating) received jobs' results into final grid task result.
<p>
<h1 class="header">Grid Task Execution Sequence</h1>
<ol>
<li>
Upon request to execute a grid task with given task name system will find
deployed task with given name. Task needs to be deployed prior to execution
(see <a href="../../../../org/apache/ignite/IgniteCompute.html#localDeployTask-java.lang.Class-java.lang.ClassLoader-"><code>IgniteCompute.localDeployTask(Class, ClassLoader)</code></a> method), however if task does not specify
its name explicitly via <a href="../../../../org/apache/ignite/compute/ComputeTaskName.html" title="annotation in org.apache.ignite.compute"><code>@ComputeTaskName</code></a> annotation, it
will be auto-deployed first time it gets executed.
</li>
<li>
System will create new distributed task session (see <a href="../../../../org/apache/ignite/compute/ComputeTaskSession.html" title="interface in org.apache.ignite.compute"><code>ComputeTaskSession</code></a>).
</li>
<li>
System will inject all annotated resources (including task session) into grid task instance.
See <a href="../../../../org/apache/ignite/resources/package-summary.html"><code>org.apache.ignite.resources</code></a> package for the list of injectable resources.
</li>
<li>
System will apply <a href="../../../../org/apache/ignite/compute/ComputeTask.html#map-java.util.List-T-"><code>map(List, Object)</code></a>. This
method is responsible for splitting business logic of grid task into
multiple grid jobs (units of execution) and mapping them to
grid nodes. Method <a href="../../../../org/apache/ignite/compute/ComputeTask.html#map-java.util.List-T-"><code>map(List, Object)</code></a> returns
a map of with grid jobs as keys and grid node as values.
</li>
<li>
System will send mapped grid jobs to their respective nodes.
</li>
<li>
Upon arrival on the remote node a grid job will be handled by collision SPI
(see <a href="../../../../org/apache/ignite/spi/collision/CollisionSpi.html" title="interface in org.apache.ignite.spi.collision"><code>CollisionSpi</code></a>) which will determine how a job will be executed
on the remote node (immediately, buffered or canceled).
</li>
<li>
Once job execution results become available method <a href="../../../../org/apache/ignite/compute/ComputeTask.html#result-org.apache.ignite.compute.ComputeJobResult-java.util.List-"><code>result(ComputeJobResult, List)</code></a>
will be called for each received job result. The policy returned by this method will
determine the way task reacts to every job result:
<ul>
<li>
If <a href="../../../../org/apache/ignite/compute/ComputeJobResultPolicy.html#WAIT"><code>ComputeJobResultPolicy.WAIT</code></a> policy is returned, task will continue to wait
for other job results. If this result is the last job result, then
<a href="../../../../org/apache/ignite/compute/ComputeTask.html#reduce-java.util.List-"><code>reduce(List)</code></a> method will be called.
</li>
<li>
If <a href="../../../../org/apache/ignite/compute/ComputeJobResultPolicy.html#REDUCE"><code>ComputeJobResultPolicy.REDUCE</code></a> policy is returned, then method
<a href="../../../../org/apache/ignite/compute/ComputeTask.html#reduce-java.util.List-"><code>reduce(List)</code></a> will be called right away without waiting for
other jobs' completion (all remaining jobs will receive a cancel request).
</li>
<li>
If <a href="../../../../org/apache/ignite/compute/ComputeJobResultPolicy.html#FAILOVER"><code>ComputeJobResultPolicy.FAILOVER</code></a> policy is returned, then job will
be failed over to another node for execution. The node to which job will get
failed over is decided by <a href="../../../../org/apache/ignite/spi/failover/FailoverSpi.html" title="interface in org.apache.ignite.spi.failover"><code>FailoverSpi</code></a> SPI implementation.
Note that if you use <a href="../../../../org/apache/ignite/compute/ComputeTaskAdapter.html" title="class in org.apache.ignite.compute"><code>ComputeTaskAdapter</code></a> adapter for <code>ComputeTask</code>
implementation, then it will automatically fail jobs to another node for 2
known failure cases:
<ul>
<li>
Job has failed due to node crash. In this case <a href="../../../../org/apache/ignite/compute/ComputeJobResult.html#getException--"><code>ComputeJobResult.getException()</code></a>
method will return an instance of <a href="../../../../org/apache/ignite/cluster/ClusterTopologyException.html" title="class in org.apache.ignite.cluster"><code>ClusterTopologyException</code></a> exception.
</li>
<li>
Job execution was rejected, i.e. remote node has cancelled job before it got
a chance to execute, while it still was on the waiting list. In this case
<a href="../../../../org/apache/ignite/compute/ComputeJobResult.html#getException--"><code>ComputeJobResult.getException()</code></a> method will return an instance of
<a href="../../../../org/apache/ignite/compute/ComputeExecutionRejectedException.html" title="class in org.apache.ignite.compute"><code>ComputeExecutionRejectedException</code></a> exception.
</li>
</ul>
</li>
</ul>
</li>
<li>
Once all results are received or <a href="../../../../org/apache/ignite/compute/ComputeTask.html#result-org.apache.ignite.compute.ComputeJobResult-java.util.List-"><code>result(ComputeJobResult, List)</code></a>
method returned <a href="../../../../org/apache/ignite/compute/ComputeJobResultPolicy.html#REDUCE"><code>ComputeJobResultPolicy.REDUCE</code></a> policy, method <a href="../../../../org/apache/ignite/compute/ComputeTask.html#reduce-java.util.List-"><code>reduce(List)</code></a>
is called to aggregate received results into one final result. Once this method is finished the
execution of the grid task is complete. This result will be returned to the user through
<a href="../../../../org/apache/ignite/compute/ComputeTaskFuture.html#get--"><code>ComputeTaskFuture.get()</code></a> method.
</li>
</ol>
<p>
<h1 class="header">Continuous Job Mapper</h1>
For cases when jobs within split are too large to fit in memory at once or when
simply not all jobs in task are known during <a href="../../../../org/apache/ignite/compute/ComputeTask.html#map-java.util.List-T-"><code>map(List, Object)</code></a> step,
use <a href="../../../../org/apache/ignite/compute/ComputeTaskContinuousMapper.html" title="interface in org.apache.ignite.compute"><code>ComputeTaskContinuousMapper</code></a> to continuously stream jobs from task even after <code>map(...)</code>
step is complete. Usually with continuous mapper the number of jobs within task
may grow too large - in this case it may make sense to use it in combination with
<a href="../../../../org/apache/ignite/compute/ComputeTaskNoResultCache.html" title="annotation in org.apache.ignite.compute"><code>@ComputeTaskNoResultCache</code></a> annotation.
<p>
<h1 class="header">Task Result Caching</h1>
Sometimes job results are too large or task simply has too many jobs to keep track
of which may hinder performance. In such cases it may make sense to disable task
result caching by attaching <a href="../../../../org/apache/ignite/compute/ComputeTaskNoResultCache.html" title="annotation in org.apache.ignite.compute"><code>@ComputeTaskNoResultCache</code></a> annotation to task class, and
processing all results as they come in <a href="../../../../org/apache/ignite/compute/ComputeTask.html#result-org.apache.ignite.compute.ComputeJobResult-java.util.List-"><code>result(ComputeJobResult, List)</code></a> method.
When Ignite sees this annotation it will disable tracking of job results and
list of all job results passed into <a href="../../../../org/apache/ignite/compute/ComputeTask.html#result-org.apache.ignite.compute.ComputeJobResult-java.util.List-"><code>result(ComputeJobResult, List)</code></a> or
<a href="../../../../org/apache/ignite/compute/ComputeTask.html#reduce-java.util.List-"><code>reduce(List)</code></a> methods will always be empty. Note that list of
job siblings on <a href="../../../../org/apache/ignite/compute/ComputeTaskSession.html" title="interface in org.apache.ignite.compute"><code>ComputeTaskSession</code></a> will also be empty to prevent number
of job siblings from growing as well.
<p>
<h1 class="header">Resource Injection</h1>
Grid task implementation can be injected using IoC (dependency injection) with
ignite resources. Both, field and method based injection are supported.
The following ignite resources can be injected:
<ul>
<li><a href="../../../../org/apache/ignite/resources/TaskSessionResource.html" title="annotation in org.apache.ignite.resources"><code>TaskSessionResource</code></a></li>
<li><a href="../../../../org/apache/ignite/resources/IgniteInstanceResource.html" title="annotation in org.apache.ignite.resources"><code>IgniteInstanceResource</code></a></li>
<li><a href="../../../../org/apache/ignite/resources/LoggerResource.html" title="annotation in org.apache.ignite.resources"><code>LoggerResource</code></a></li>
<li><a href="../../../../org/apache/ignite/resources/SpringApplicationContextResource.html" title="annotation in org.apache.ignite.resources"><code>SpringApplicationContextResource</code></a></li>
<li><a href="../../../../org/apache/ignite/resources/SpringResource.html" title="annotation in org.apache.ignite.resources"><code>SpringResource</code></a></li>
</ul>
Refer to corresponding resource documentation for more information.
<p>
<h1 class="header">Grid Task Adapters</h1>
<code>ComputeTask</code> comes with several convenience adapters to make the usage easier:
<ul>
<li>
<a href="../../../../org/apache/ignite/compute/ComputeTaskAdapter.html" title="class in org.apache.ignite.compute"><code>ComputeTaskAdapter</code></a> provides default implementation for <a href="../../../../org/apache/ignite/compute/ComputeTask.html#result-org.apache.ignite.compute.ComputeJobResult-java.util.List-"><code>result(ComputeJobResult, List)</code></a>
method which provides automatic fail-over to another node if remote job has failed
due to node crash (detected by <a href="../../../../org/apache/ignite/cluster/ClusterTopologyException.html" title="class in org.apache.ignite.cluster"><code>ClusterTopologyException</code></a> exception) or due to job
execution rejection (detected by <a href="../../../../org/apache/ignite/compute/ComputeExecutionRejectedException.html" title="class in org.apache.ignite.compute"><code>ComputeExecutionRejectedException</code></a> exception).
Here is an example of how a you would implement your task using <a href="../../../../org/apache/ignite/compute/ComputeTaskAdapter.html" title="class in org.apache.ignite.compute"><code>ComputeTaskAdapter</code></a>:
<pre name="code" class="java">
public class MyFooBarTask extends ComputeTaskAdapter&lt;String, String&gt; {
// Inject load balancer.
&#64;LoadBalancerResource
ComputeLoadBalancer balancer;
// Map jobs to grid nodes.
public Map&lt;? extends ComputeJob, ClusterNode&gt; map(List&lt;ClusterNode&gt; subgrid, String arg) throws IgniteCheckedException {
Map&lt;MyFooBarJob, ClusterNode&gt; jobs = new HashMap&lt;MyFooBarJob, ClusterNode&gt;(subgrid.size());
// In more complex cases, you can actually do
// more complicated assignments of jobs to nodes.
for (int i = 0; i &lt; subgrid.size(); i++) {
// Pick the next best balanced node for the job.
jobs.put(new MyFooBarJob(arg), balancer.getBalancedNode())
}
return jobs;
}
// Aggregate results into one compound result.
public String reduce(List&lt;ComputeJobResult&gt; results) throws IgniteCheckedException {
// For the purpose of this example we simply
// concatenate string representation of every
// job result
StringBuilder buf = new StringBuilder();
for (ComputeJobResult res : results) {
// Append string representation of result
// returned by every job.
buf.append(res.getData().string());
}
return buf.string();
}
}
</pre>
</li>
<li>
<a href="../../../../org/apache/ignite/compute/ComputeTaskSplitAdapter.html" title="class in org.apache.ignite.compute"><code>ComputeTaskSplitAdapter</code></a> hides the job-to-node mapping logic from
user and provides convenient <a href="../../../../org/apache/ignite/compute/ComputeTaskSplitAdapter.html#split-int-T-"><code>ComputeTaskSplitAdapter.split(int, Object)</code></a>
method for splitting task into sub-jobs in homogeneous environments.
Here is an example of how you would implement your task using <a href="../../../../org/apache/ignite/compute/ComputeTaskSplitAdapter.html" title="class in org.apache.ignite.compute"><code>ComputeTaskSplitAdapter</code></a>:
<pre name="code" class="java">
public class MyFooBarTask extends ComputeTaskSplitAdapter&lt;Object, String&gt; {
&#64;Override
protected Collection&lt;? extends ComputeJob&gt; split(int gridSize, Object arg) throws IgniteCheckedException {
List&lt;MyFooBarJob&gt; jobs = new ArrayList&lt;MyFooBarJob&gt;(gridSize);
for (int i = 0; i &lt; gridSize; i++) {
jobs.add(new MyFooBarJob(arg));
}
// Node assignment via load balancer
// happens automatically.
return jobs;
}
// Aggregate results into one compound result.
public String reduce(List&lt;ComputeJobResult&gt; results) throws IgniteCheckedException {
// For the purpose of this example we simply
// concatenate string representation of every
// job result
StringBuilder buf = new StringBuilder();
for (ComputeJobResult res : results) {
// Append string representation of result
// returned by every job.
buf.append(res.getData().string());
}
return buf.string();
}
}
</pre>
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<h3>Method Summary</h3>
<table class="memberSummary" border="0" cellpadding="3" cellspacing="0" summary="Method Summary table, listing methods, and an explanation">
<caption><span id="t0" class="activeTableTab"><span>All Methods</span><span class="tabEnd">&nbsp;</span></span><span id="t2" class="tableTab"><span><a href="javascript:show(2);">Instance Methods</a></span><span class="tabEnd">&nbsp;</span></span><span id="t3" class="tableTab"><span><a href="javascript:show(4);">Abstract Methods</a></span><span class="tabEnd">&nbsp;</span></span></caption>
<tr>
<th class="colFirst" scope="col">Modifier and Type</th>
<th class="colLast" scope="col">Method and Description</th>
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<tr id="i0" class="altColor">
<td class="colFirst"><code><a href="http://docs.oracle.com/javase/8/docs/api/java/util/Map.html?is-external=true" title="class or interface in java.util">Map</a>&lt;? extends <a href="../../../../org/apache/ignite/compute/ComputeJob.html" title="interface in org.apache.ignite.compute">ComputeJob</a>,<a href="../../../../org/apache/ignite/cluster/ClusterNode.html" title="interface in org.apache.ignite.cluster">ClusterNode</a>&gt;</code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../org/apache/ignite/compute/ComputeTask.html#map-java.util.List-T-">map</a></span>(<a href="http://docs.oracle.com/javase/8/docs/api/java/util/List.html?is-external=true" title="class or interface in java.util">List</a>&lt;<a href="../../../../org/apache/ignite/cluster/ClusterNode.html" title="interface in org.apache.ignite.cluster">ClusterNode</a>&gt;&nbsp;subgrid,
<a href="../../../../org/apache/ignite/compute/ComputeTask.html" title="type parameter in ComputeTask">T</a>&nbsp;arg)</code>
<div class="block">This method is called to map or split grid task into multiple grid jobs.</div>
</td>
</tr>
<tr id="i1" class="rowColor">
<td class="colFirst"><code><a href="../../../../org/apache/ignite/compute/ComputeTask.html" title="type parameter in ComputeTask">R</a></code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../org/apache/ignite/compute/ComputeTask.html#reduce-java.util.List-">reduce</a></span>(<a href="http://docs.oracle.com/javase/8/docs/api/java/util/List.html?is-external=true" title="class or interface in java.util">List</a>&lt;<a href="../../../../org/apache/ignite/compute/ComputeJobResult.html" title="interface in org.apache.ignite.compute">ComputeJobResult</a>&gt;&nbsp;results)</code>
<div class="block">Reduces (or aggregates) results received so far into one compound result to be returned to
caller via <a href="../../../../org/apache/ignite/compute/ComputeTaskFuture.html#get--"><code>ComputeTaskFuture.get()</code></a> method.</div>
</td>
</tr>
<tr id="i2" class="altColor">
<td class="colFirst"><code><a href="../../../../org/apache/ignite/compute/ComputeJobResultPolicy.html" title="enum in org.apache.ignite.compute">ComputeJobResultPolicy</a></code></td>
<td class="colLast"><code><span class="memberNameLink"><a href="../../../../org/apache/ignite/compute/ComputeTask.html#result-org.apache.ignite.compute.ComputeJobResult-java.util.List-">result</a></span>(<a href="../../../../org/apache/ignite/compute/ComputeJobResult.html" title="interface in org.apache.ignite.compute">ComputeJobResult</a>&nbsp;res,
<a href="http://docs.oracle.com/javase/8/docs/api/java/util/List.html?is-external=true" title="class or interface in java.util">List</a>&lt;<a href="../../../../org/apache/ignite/compute/ComputeJobResult.html" title="interface in org.apache.ignite.compute">ComputeJobResult</a>&gt;&nbsp;rcvd)</code>
<div class="block">Asynchronous callback invoked every time a result from remote execution is
received.</div>
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<h4>map</h4>
<pre>@Nullable
<a href="http://docs.oracle.com/javase/8/docs/api/java/util/Map.html?is-external=true" title="class or interface in java.util">Map</a>&lt;? extends <a href="../../../../org/apache/ignite/compute/ComputeJob.html" title="interface in org.apache.ignite.compute">ComputeJob</a>,<a href="../../../../org/apache/ignite/cluster/ClusterNode.html" title="interface in org.apache.ignite.cluster">ClusterNode</a>&gt;&nbsp;map(<a href="http://docs.oracle.com/javase/8/docs/api/java/util/List.html?is-external=true" title="class or interface in java.util">List</a>&lt;<a href="../../../../org/apache/ignite/cluster/ClusterNode.html" title="interface in org.apache.ignite.cluster">ClusterNode</a>&gt;&nbsp;subgrid,
@Nullable
<a href="../../../../org/apache/ignite/compute/ComputeTask.html" title="type parameter in ComputeTask">T</a>&nbsp;arg)
throws <a href="../../../../org/apache/ignite/IgniteException.html" title="class in org.apache.ignite">IgniteException</a></pre>
<div class="block">This method is called to map or split grid task into multiple grid jobs. This is the
first method that gets called when task execution starts.</div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>arg</code> - Task execution argument. Can be <code>null</code>. This is the same argument
as the one passed into <code>Grid#execute(...)</code> methods.</dd>
<dd><code>subgrid</code> - Nodes available for this task execution. Note that order of nodes is
guaranteed to be randomized by container. This ensures that every time
you simply iterate through grid nodes, the order of nodes will be random which
over time should result into all nodes being used equally.</dd>
<dt><span class="returnLabel">Returns:</span></dt>
<dd>Map of grid jobs assigned to subgrid node. Unless <a href="../../../../org/apache/ignite/compute/ComputeTaskContinuousMapper.html" title="interface in org.apache.ignite.compute"><code>ComputeTaskContinuousMapper</code></a> is
injected into task, if <code>null</code> or empty map is returned, exception will be thrown.</dd>
<dt><span class="throwsLabel">Throws:</span></dt>
<dd><code><a href="../../../../org/apache/ignite/IgniteException.html" title="class in org.apache.ignite">IgniteException</a></code> - If mapping could not complete successfully. This exception will be
thrown out of <a href="../../../../org/apache/ignite/compute/ComputeTaskFuture.html#get--"><code>ComputeTaskFuture.get()</code></a> method.</dd>
</dl>
</li>
</ul>
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<h4>result</h4>
<pre><a href="../../../../org/apache/ignite/compute/ComputeJobResultPolicy.html" title="enum in org.apache.ignite.compute">ComputeJobResultPolicy</a>&nbsp;result(<a href="../../../../org/apache/ignite/compute/ComputeJobResult.html" title="interface in org.apache.ignite.compute">ComputeJobResult</a>&nbsp;res,
<a href="http://docs.oracle.com/javase/8/docs/api/java/util/List.html?is-external=true" title="class or interface in java.util">List</a>&lt;<a href="../../../../org/apache/ignite/compute/ComputeJobResult.html" title="interface in org.apache.ignite.compute">ComputeJobResult</a>&gt;&nbsp;rcvd)
throws <a href="../../../../org/apache/ignite/IgniteException.html" title="class in org.apache.ignite">IgniteException</a></pre>
<div class="block">Asynchronous callback invoked every time a result from remote execution is
received. It is ultimately upto this method to return a policy based
on which the system will either wait for more results, reduce results
received so far, or failover this job to another node. See
<a href="../../../../org/apache/ignite/compute/ComputeJobResultPolicy.html" title="enum in org.apache.ignite.compute"><code>ComputeJobResultPolicy</code></a> for more information about result policies.</div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>res</code> - Received remote grid executable result.</dd>
<dd><code>rcvd</code> - All previously received results. Note that if task class has
<a href="../../../../org/apache/ignite/compute/ComputeTaskNoResultCache.html" title="annotation in org.apache.ignite.compute"><code>ComputeTaskNoResultCache</code></a> annotation, then this list will be empty.</dd>
<dt><span class="returnLabel">Returns:</span></dt>
<dd>Result policy that dictates how to process further upcoming
job results.</dd>
<dt><span class="throwsLabel">Throws:</span></dt>
<dd><code><a href="../../../../org/apache/ignite/IgniteException.html" title="class in org.apache.ignite">IgniteException</a></code> - If handling a job result caused an error. This exception will
be thrown out of <a href="../../../../org/apache/ignite/compute/ComputeTaskFuture.html#get--"><code>ComputeTaskFuture.get()</code></a> method.</dd>
</dl>
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<h4>reduce</h4>
<pre>@Nullable
<a href="../../../../org/apache/ignite/compute/ComputeTask.html" title="type parameter in ComputeTask">R</a>&nbsp;reduce(<a href="http://docs.oracle.com/javase/8/docs/api/java/util/List.html?is-external=true" title="class or interface in java.util">List</a>&lt;<a href="../../../../org/apache/ignite/compute/ComputeJobResult.html" title="interface in org.apache.ignite.compute">ComputeJobResult</a>&gt;&nbsp;results)
throws <a href="../../../../org/apache/ignite/IgniteException.html" title="class in org.apache.ignite">IgniteException</a></pre>
<div class="block">Reduces (or aggregates) results received so far into one compound result to be returned to
caller via <a href="../../../../org/apache/ignite/compute/ComputeTaskFuture.html#get--"><code>ComputeTaskFuture.get()</code></a> method.
<p>
Note, that if some jobs did not succeed and could not be failed over then the list of
results passed into this method will include the failed results. Otherwise, failed
results will not be in the list.</div>
<dl>
<dt><span class="paramLabel">Parameters:</span></dt>
<dd><code>results</code> - Received results of broadcasted remote executions. Note that if task class has
<a href="../../../../org/apache/ignite/compute/ComputeTaskNoResultCache.html" title="annotation in org.apache.ignite.compute"><code>ComputeTaskNoResultCache</code></a> annotation, then this list will be empty.</dd>
<dt><span class="returnLabel">Returns:</span></dt>
<dd>Grid job result constructed from results of remote executions.</dd>
<dt><span class="throwsLabel">Throws:</span></dt>
<dd><code><a href="../../../../org/apache/ignite/IgniteException.html" title="class in org.apache.ignite">IgniteException</a></code> - If reduction or results caused an error. This exception will
be thrown out of <a href="../../../../org/apache/ignite/compute/ComputeTaskFuture.html#get--"><code>ComputeTaskFuture.get()</code></a> method.</dd>
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<p class="legalCopy"><small><table width="100%" border="0" cellspacing=0 cellpadding=0 style="padding: 5px"> <tr> <td> <table style="padding-left: 0; margin: 0"> <tbody style="padding: 0; margin: 0"> <tr style="padding: 0; margin: 0"> <td> <a target=_blank href="https://ignite.apache.org"><nobr>2018 Copyright &#169; Apache Software Foundation</nobr></a> </td> </tr> </tbody> </table> </td> <td width="100%" align="right" valign="center"> <a href="https://twitter.com/ApacheIgnite" class="twitter-follow-button" data-show-count="false" data-size="large">Follow @ApacheIgnite</a> </td> </tr> <tr> <td colspan="2" valign="top" align="left"> <table style="padding-left: 0; margin: 0"> <tbody style="padding: 0; margin: 0"> <tr style="padding: 0; margin: 0"> <td> <b>Ignite Fabric</b> </td> <td>:&nbsp;&nbsp; ver. <strong>2.6.0</strong> </td> </tr> <tr style="padding: 0; margin: 0"> <td> <b>Release Date</b> </td> <td>:&nbsp;&nbsp; July 10 2018 </td> </tr> </tbody> </table> </td> </tr> </table></small></p>
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