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35 lines
1.7 KiB
TeX
35 lines
1.7 KiB
TeX
\subsection{\code{nowait} Clause on \code{target} Construct}
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\label{subsec:target_nowait_clause}
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\index{target construct@\code{target} construct!nowait clause@\code{nowait} clause}
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\index{clauses!nowait@\code{nowait}}
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\index{nowait clause@\code{nowait} clause}
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The following example shows how to execute code asynchronously on a
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device without an explicit task. The \code{nowait} clause on a \code{target}
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construct allows the thread of the \plc{target task} to perform other
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work while waiting for the \code{target} region execution to complete.
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Hence, the \code{target} region can execute asynchronously on the
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device (without requiring a host thread to idle while waiting for
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the \plc{target task} execution to complete).
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In this example the product of two vectors (arrays), \plc{v1}
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and \plc{v2}, is formed. One half of the operations is performed
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on the device, and the last half on the host, concurrently.
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After a team of threads is formed the primary thread generates
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the \plc{target task} while the other threads can continue on, without a barrier,
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to the execution of the host portion of the vector product.
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The completion of the \plc{target task} (asynchronous target execution) is
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guaranteed by the synchronization in the implicit barrier at the end of the
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host vector-product worksharing loop region. See the \code{barrier}
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glossary entry in the OpenMP specification for details.
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The host loop scheduling is \code{dynamic}, to balance the host thread executions, since
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one thread is being used for offload generation. In the situation where
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little time is spent by the \plc{target task} in setting
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up and tearing down the target execution, \code{static} scheduling may be desired.
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\cexample[5.1]{async_target}{3}
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\ffreeexample[5.1]{async_target}{3}
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