kernel
A valid kernel object.
arg_index
The argument index. Arguments to the kernel are referred by indices that go from 0 for the leftmost argument to n - 1, where n is the total number of arguments declared by a kernel.
arg_value
A pointer to data that should be used as the argument value for argument specified
by arg_index
. The argument data pointed to by arg_value
is copied and the arg_value
pointer can therefore be reused by the application after clSetKernelArg
returns. The argument value specified is the value used by all API calls that enqueue kernel
(clEnqueueNDRangeKernel and
clEnqueueTask) until the argument value is changed by a call to clSetKernelArg
for kernel
.
If the argument is a memory object (buffer or image), the arg_value
entry will be a
pointer to the appropriate buffer or image object. The memory object must be created with the context
associated with the kernel object. A NULL value can also be specified if the argument is a buffer
object in which case a NULL value will be used as the value for the argument declared as a
pointer to __global
or __constant
memory in the kernel. If the
argument is declared with the __local
qualifier, the arg_value
entry must be NULL. If the argument is of type sampler_t
, the arg_value
entry must be a pointer to the sampler object.
If the argument is declared to be a pointer of a built-in or user defined type with
the __global
or __constant
qualifier, the memory object specified as
argument value must be a buffer object (or NULL). If the argument is declared with the __constant
qualifier, the size in bytes of the memory object cannot exceed CL_DEVICE_MAX_CONSTANT_BUFFER_SIZE and the
number of arguments declared with the __constant
qualifier cannot exceed
CL_DEVICE_MAX_CONSTANT_ARGS.
The memory object specified as argument value must be a 2D image object if the argument is
declared to be of type image2d_t
. The memory object specified as argument value must
be a 3D image object if argument is declared to be of type image3d_t
.
For all other kernel arguments, the arg_value
entry must be a pointer to the actual
data to be used as argument value.
arg_size
Specifies the size of the argument value. If the argument is a memory object, the size is
the size of the buffer or image object type. For arguments declared with the __local
qualifier, the size specified will be the size in bytes of the buffer that must be allocated
for the __local
argument. If the argument is of type sampler_t
,
the arg_size
value must be equal to sizeof(cl_sampler)
. For all other
arguments, the size will be the size of argument type.
A kernel object does not update the reference count for objects such as memory, sampler
objects specified as argument values by clSetKernelArg
. Users may not rely on a kernel object
to retain objects specified as argument values to the kernel.
Implementations shall not allow cl_kernel objects to hold reference counts to cl_kernel arguments, because no
mechanism is provided for the user to tell the kernel to release that ownership right. If the kernel holds ownership
rights on kernel args, that would make it impossible for the user to tell with certainty when he may safely release
user allocated resources associated with OpenCL objects such as the cl_mem backing store used with
CL_MEM_USE_HOST_PTR
.
An OpenCL API call is considered to be thread-safe if the internal state as managed by OpenCL remains consistent when called simultaneously by multiple host threads. OpenCL API calls that are thread-safe allow an application to call these functions in multiple host threads without having to implement mutual exclusion across these host threads i.e. they are also re-entrant-safe.
All OpenCL API calls are thread-safe except clSetKernelArg
, which is safe to call
from any host thread, and is safe to call re-entrantly so long as concurrent calls operate on
different cl_kernel objects. However, the behavior of the cl_kernel object is undefined if
clSetKernelArg
is called from multiple host threads on the same cl_kernel object at the same
time.
There is an inherent race condition in the design of OpenCL that occurs between setting a kernel argument and using the kernel with clEnqueueNDRangeKernel or clEnqueueTask. Another host thread might change the kernel arguments between when a host thread sets the kernel arguments and then enqueues the kernel, causing the wrong kernel arguments to be enqueued. Rather than attempt to share cl_kernel objects among multiple host threads, applications are strongly encouraged to make additional cl_kernel objects for kernel functions for each host thread.
clSetKernelArg
returns CL_SUCCESS if the function is
executed successfully. Otherwise, it returns one of the following errors:
kernel
is not a valid kernel object.
arg_index
is not a valid argument index.
arg_value
specified is NULL for an argument that is not
declared with the __local
qualifier or vice-versa.
arg_value
is not a valid memory object.
sampler_t
when
the specified arg_value
is not a valid sampler object.
arg_size
does not match the size of the
data type for an argument that is not a memory object or if the argument is a memory object
and arg_size
!= sizeof(cl_mem)
or if arg_size
is zero
and the argument is declared with the __local
qualifier or if the argument is a sampler and arg_size
!= sizeof(cl_sampler)
.
__kernel void image_filter (int n, int m, __constant float *filter_weights, __read_only image2d_t src_image, __write_only image2d_t dst_image) { ... } |
Argument index values for image_filter
will be 0 for n, 1 for m, 2 for
filter_weights
, 3 for src_image
and 4 for dst_image
.
clCreateKernel, clCreateKernelsInProgram, clReleaseKernel, clRetainKernel, clGetKernelInfo, clGetKernelWorkGroupInfo