74 lines
2.4 KiB
Plaintext
74 lines
2.4 KiB
Plaintext
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// Occasionally, it is advantageous to avoid initializing the individual
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// elements of a device_vector. For example, the default behavior of
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// zero-initializing numeric data may introduce undesirable overhead.
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// This example demonstrates how to avoid default construction of a
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// device_vector's data by using a custom allocator.
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#include <thrust/device_allocator.h>
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#include <thrust/device_vector.h>
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#include <thrust/functional.h>
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#include <thrust/logical.h>
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#include <cassert>
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// uninitialized_allocator is an allocator which
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// derives from device_allocator and which has a
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// no-op construct member function
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template <typename T>
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struct uninitialized_allocator : thrust::device_allocator<T>
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{
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// the default generated constructors and destructors are implicitly
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// marked __host__ __device__, but the current Thrust device_allocator
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// can only be constructed and destroyed on the host; therefore, we
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// define these as host only
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__host__ uninitialized_allocator() {} // NOLINT(modernize-use-equals-default)
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__host__ uninitialized_allocator(const uninitialized_allocator& other)
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: thrust::device_allocator<T>(other)
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{}
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__host__ ~uninitialized_allocator() {} // NOLINT(modernize-use-equals-default)
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uninitialized_allocator& operator=(const uninitialized_allocator&) = default;
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// for correctness, you should also redefine rebind when you inherit
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// from an allocator type; this way, if the allocator is rebound somewhere,
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// it's going to be rebound to the correct type - and not to its base
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// type for U
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template <typename U>
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struct rebind
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{
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using other = uninitialized_allocator<U>;
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};
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// note that construct is annotated as
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// a __host__ __device__ function
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__host__ __device__ void construct(T*)
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{
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// no-op
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}
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};
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// to make a device_vector which does not initialize its elements,
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// use uninitialized_allocator as the 2nd template parameter
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using uninitialized_vector = thrust::device_vector<float, uninitialized_allocator<float>>;
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int main()
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{
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uninitialized_vector vec(10);
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// the initial value of vec's 10 elements is undefined
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// resize without default value does not initialize elements
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vec.resize(20);
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// resize with default value does initialize elements
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vec.resize(30, 13);
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// the value of elements [0,20) is still undefined
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// but the value of elements [20,30) is 13:
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using namespace thrust::placeholders;
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assert(thrust::all_of(vec.begin() + 20, vec.end(), _1 == 13));
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return 0;
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}
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