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, image or image array), the
arg_value
entry will be a pointer to the appropriate
buffer, image or image array object. The memory object must be created
with the context associated with the kernel object. If the argument
is a buffer object, the arg_value
pointer can be
NULL or point to a NULL value 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 scalar or vector
type, or a user defined structure type in the global or constant address
space, 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 as pointers to __constant
memory 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. The memory object specified as argument value must be a 1D image object if the argument is declared to be of type image1d_t. The memory object specified as argument value must be a 1D image buffer object if the argument is declared to be of type image1d_buffer_t. The memory object specified as argument value must be a 1D image array object if argument is declared to be of type image1d_array_t. The memory object specified as argument value must be a 2D image array object if argument is declared to be of type image2d_array_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
. clSetKernelArg
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. Please note that there
are additional limitations as to which OpenCL APIs may be called from OpenCL callback
functions -- please see section 5.9.
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 not a valid value.
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)
.
read_only
qualifier and arg_value
refers to an image object created with cl_mem_flags
of
CL_MEM_WRITE
or if the image argument is declared with
the write_only
qualifier and arg_value
refers to an image object created with cl_mem_flags
of
CL_MEM_READ
.
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