clCreateContext

Creates an OpenCL context.

cl_context clCreateContext( const cl_context_properties *properties,
  cl_uint num_devices,
  const cl_device_id *devices,
  void ( CL_CALLBACK  *pfn_notify) (

const char *errinfo,
                        const void *private_info, size_t cb,
                        void *user_data

),
  void *user_data,
  cl_int *errcode_ret)

Description

An OpenCL context is created with one or more devices. Contexts are used by the OpenCL runtime for managing objects such as command-queues, memory, program and kernel objects and for executing kernels on one or more devices specified in the context.

Parameters

properties

Specifies a list of context property names and their corresponding values. Each property name is immediately followed by the corresponding desired value. The list is terminated with 0. properties can be NULL in which case the platform that is selected is implementation-defined. The list of supported properties is described in the table below.

If the extension cl_khr_dx9_media_sharing is enabled, then properties specifies a list of context property names and their corresponding values. Each property is followed immediately by the corresponding desired value. The list is terminated with zero. If a property is not specified in properties, then its default value (listed in the table below) is used (it is said to be specified implicitly). If properties is NULL or empty (points to a list whose first value is zero), all attributes take on their default values.

If the extension cl_khr_d3d10_sharing is enabled, then properties specifies a list of context property names and their corresponding values. Each property is followed immediately by the corresponding desired value. The list is terminated with zero. if a property is not specified in properties, then its default value is used (it is said to be specified implicitly). If properties is NULL or empty (points to a list whose first value is zero), all attributes take on their default value.

If the extension cl_khr_d3d11_sharing is enabled, then properties specifies a list of context property names and their corresponding values. Each property is followed immediately by the corresponding desired value. The list is terminated with zero. If a property is not specified in properties, then its default value is used (it is said to be specified implicitly). If properties is NULL or empty (points to a list whose first value is zero), all attributes take on their default value.

If the extension cl_khr_gl_sharing is enabled, then properties points to an attribute list, which is a array of ordered <attribute name, value> pairs terminated with zero. If an attribute is not specified in properties, then its default value is used (it is said to be specified implicitly). If properties is NULL or empty (points to a list whose first value is zero), all attributes take on their default values.

List of supported properties (Table 4.5)

cl_context_properties enum Property value Description
CL_CONTEXT_PLATFORM cl_platform_id Specifies the platform to use.
CL_CONTEXT_INTEROP_USER_SYNC cl_bool Specifies whether the user is responsible for synchronization between OpenCL and other APIs. Please refer to the specific sections in the OpenCL 2.0 extension specification that describe sharing with other APIs for restrictions on using this flag. If CL_CONTEXT_INTEROP_USER_SYNC is not specified, a default of CL_FALSE is assumed.
CL_CONTEXT_D3D10_DEVICE_KHR ID3D10Device * Specifies the ID3D10Device * to use for Direct3D 10 interoperability. The default value is NULL (applies if the extension cl_khr_d3d10_sharing is supported)
CL_CONTEXT_ADAPTER_D3D9_KHR IDirect3DDevice9 * Specifies an IDirect3DDevice9 to use for D3D9 interop (applies if the cl_khr_dx9_media_sharing extension is supported)
CL_CONTEXT_ADAPTER_D3D9EX_KHR IDirect3DDeviceEx * Specifies an IDirect3DDevice9Ex to use for D3D9 interop (applies if the cl_khr_dx9_media_sharing extension is supported)
CL_CONTEXT_ADAPTER_DXVA_KHR IDXVAHD_Device * Specifies an IDXVAHD_Device to use for DXVA interop (applies if the cl_khr_dx9_media_sharing extension is supported)
CL_GL_CONTEXT_KHR 0, OpenGL context handle OpenGL context to associated the OpenCL context with (available if the cl_khr_gl_sharing extension is enabled)
CL_CGL_SHAREGROUP_KHR 0, CGL share group handle CGL share group to associate the OpenCL context with (available if the cl_khr_gl_sharing extension is enabled)
CL_EGL_DISPLAY_KHR EGL_NO_DISPLAY, EGLDisplay handle EGLDisplay an OpenGL context was created with respect to (available if the cl_khr_gl_sharing extension is enabled)
CL_GLX_DISPLAY_KHR None, X handle X Display an OpenGL context was created with respect to (available if the cl_khr_gl_sharing extension is enabled)
CL_WGL_HDC_KHR 0, HDC handle HDC an OpenGL context was created with respect to (available if the cl_khr_gl_sharing extension is enabled)
CL_CONTEXT_D3D11_DEVICE_KHR ID3D11Device * Specifies the ID3D11Device * to use for Direct3D 11 interoperability. The default value is NULL. (Applies if the cl_khr_d3d11_sharing extension is supported.)
CL_CONTEXT_MEMORY_INITIALIZE_KHR cl_context_memory- _initialize_khr

Describes which memory types for the context must be initialized. This is a bit-field, where the following values are currently supported:

CL_CONTEXT_MEMORY_INITIALIZE_LOCAL_KHR - Initialize local memory to zeros.

CL_CONTEXT_MEMORY_INITIALIZE_PRIVATE_KHR - Initialize private memory to zeros.

(applies if the cl_khr_initialize_memory extension is supported)

CL_CONTEXT_TERMINATE_KHR cl_bool Specifies whether the context can be terminated. The default value is CL_FALSE. (applies if the cl_khr_terminate_context extension is supported)
num_devices

The number of devices specified in the devices argument.

devices

A pointer to a list of unique devices returned by clGetDeviceIDs or sub-devices created by clCreateSubDevices for a platform. Duplicate devices specified in devices are ignored.

pfn_notify

A callback function that can be registered by the application. This callback function will be used by the OpenCL implementation to report information on errors during context creation as well as errors that occur at runtime in this context. This callback function may be called asynchronously by the OpenCL implementation. It is the application's responsibility to ensure that the callback function is thread-safe. If pfn_notify is NULL, no callback function is registered. The parameters to this callback function are:

errinfo is a pointer to an error string.

private_info and cb represent a pointer to binary data that is returned by the OpenCL implementation that can be used to log additional information helpful in debugging the error.

user_data is a pointer to user supplied data.

NOTE: There are a number of cases where error notifications need to be delivered due to an error that occurs outside a context. Such notifications may not be delivered through the pfn_notify callback. Where these notifications go is implementation-defined.

user_data

Passed as the user_data argument when pfn_notify is called. user_data can be NULL.

errcode_ret

Returns an appropriate error code. If errcode_ret is NULL, no error code is returned.

Notes

clCreateContext and clCreateContextFromType perform an implicit retain. This is very helpful for 3rd party libraries, which typically get a context passed to them by the application. However, it is possible that the application may delete the context without informing the library. Allowing functions to attach to (i.e. retain) and release a context solves the problem of a context being used by a library no longer being valid.

If the cl_khr_terminate_context extension is enabled, CL_CONTEXT_TERMINATE_KHR can be specified in the context properties only if all devices associated with the context support the ability to support context termination (i.e. CL_DEVICE_TERMINATE_CAPABILITY_CONTEXT_KHR is set for CL_DEVICE_TERMINATE_CAPABILITY_KHR). Otherwise, context creation fails with error code of CL_INVALID_PROPERTY.

If the cl_khr_gl_sharing extension is enabled: Attributes control sharing of OpenCL memory objects with OpenGL buffer, texture, and renderbuffer objects as described in section 9.7. Depending on the platform-specific API used to bind OpenGL contexts to the window system, the following attributes may be set to identify an OpenGL context:

  • When the CGL binding API is supported, the attribute CL_CGL_SHAREGROUP_KHR should be set to a CGLShareGroup handle to a CGL share group object.
  • When the EGL binding API is supported, the attribute CL_GL_CONTEXT_KHR should be set to an EGLContexthandle to an OpenGL ES or OpenGL context, and the attribute CL_EGL_DISPLAY_KHR should be set to the EGLDisplay handle of the display used to create the OpenGL ES or OpenGL context.
  • When the GLX binding API is supported, the attribute CL_GL_CONTEXT_KHR should be set to a GLXContext handle to an OpenGL context, and the attribute CL_GLX_DISPLAY_KHR should be set to the Display handle of the X Window System display used to create the OpenGL context.
  • When the WGL binding API is supported, the attribute CL_GL_CONTEXT_KHR should be set to an HGLRC handle to an OpenGL context, and the attribute CL_WGL_HDC_KHR should be set to the HDC handle of the display used to create the OpenGL context.

If the cl_khr_gl_sharing extension is enabled: Memory objects created in the context so specified may be shared with the specified OpenGL or OpenGL ES context (as well as with any other OpenGL contexts on the share list of that context, according to the description of sharing in the GLX 1.4 and EGL 1.4 specifications, and the WGL documentation for OpenGL implementations on Microsoft Windows), or with the explicitly identified OpenGL share group for CGL. If no OpenGL or OpenGL ES context or share group is specified in the attribute list, then memory objects may not be shared, and calling any of the commands in section 9.7 will result in a CL_INVALID_GL_SHAREGROUP_REFERENCE_KHR error.

Errors

clCreateContext returns a valid non-zero context and errcode_ret is set to CL_SUCCESS if the context is created successfully. Otherwise, it returns NULL value with the following error values returned in errcode_ret:

  • CL_INVALID_PLATFORM if properties is NULL and no platform could be selected or if platform value specified in properties is not a valid platform. (If the extension cl_khr_gl_sharing is enabled, then this error is replaced with CL_INVALID_GL_SHAREGROUP_REFERENCE_KHR; see below.)
  • CL_INVALID_PROPERTY if context property name in properties is not a supported property name, if the value specified for a supported property name is not valid, or if the same property name is specified more than once. However if the extension cl_khr_gl_sharing is enabled, then CL_INVALID_PROPERTY is returned if an attribute name other than those listed in the table for properties above or if CL_CONTEXT_INTEROP_USER_SYNC is specified in properties.
  • CL_INVALID_PROPERTY if the cl_khr_gl_sharing extension is enabled and an attribute name other than those specified in the table above (table 4.5) or if CL_CONTEXT_INTEROP_USER_SYNC is specified in properties.
  • CL_INVALID_VALUE if devices is NULL; if num_devices is equal to zero; or if pfn_notify is NULL but user_data is not NULL.
  • CL_INVALID_DEVICE if devices contains an invalid device.
  • CL_INVALID_OPERATION if Direct3D 10 interoperability is specified by setting CL_INVALID_D3D10_DEVICE_KHR to a non-NULL value, and interoperability with another graphics API is also specified (if the cl_khr_d3d10_sharing extension is enabled).
  • CL_DEVICE_NOT_AVAILABLE if a device in devices is currently not available even though the device was returned by clGetDeviceIDs.
  • CL_OUT_OF_RESOURCES if there is a failure to allocate resources required by the OpenCL implementation on the device.
  • CL_OUT_OF_HOST_MEMORY if there is a failure to allocate resources required by the OpenCL implementation on the host.
  • CL_INVALID_D3D10_DEVICE_KHR if the Direct3D 10 device specified for interoperability is not compatible with the devices against which the context is to be created (if the cl_khr_d3d10_sharing extension is enabled).
  • CL_INVALID_D3D10_DEVICE_KHR if the value of the property CL_CONTEXT_D3D10_DEVICE_KHR is non-NULL and does not specify a valid Direct3D 10 device with which the cl_device_ids against which this context is to be created may interoperate (if the cl_khr_d3d10_sharing extension is enabled).
  • CL_INVALID_GL_SHAREGROUP_REFERENCE_KHR when an invalid OpenGL context or share group object handle is specified in properties (only if the cl_khr_gl_sharing extension is enabled).
  • CL_INVALID_GL_SHAREGROUP_REFERENCE_KHR if no OpenGL or OpenGL ES context or share group is specified in the attribute list given to clCreateContext and any of the commands in section 9.7 are called. (if the cl_khr_gl_sharing extension is enabled)
  • CL_INVALID_GL_SHAREGROUP_REFERENCE_KHR if the cl_khr_gl_sharing extension is enabled and if a context was specified by any of the following means:
    • A context specified for an EGL-based OpenGL ES or OpenGL implementation by setting the attributes CL_GL_CONTEXT_KHR and CL_EGL_DISPLAY_KHR.
    • A context was specified for a GLX-based OpenGL implementation by setting the attributes CL_GL_CONTEXT_KHR and CL_GLX_DISPLAY_KHR.
    • A context was specified for a WGL-based OpenGL implementation by setting the attributes CL_GL_CONTEXT_KHR and CL_WGL_HDC_KHR.
    and any of the following conditions hold:
    • The specified display and context attributes do not identify a valid OpenGL or OpenGL ES context.
    • The specified context does not support buffer and renderbuffer objects.
    • The specified context is not compatible with the OpenCL context being created (for example, it exists in a physically distinct address space, such as another hardware device, or does not support sharing data with OpenCL due to implementation restrictions).
  • CL_INVALID_GL_SHAREGROUP_REFERENCE_KHR if a share group was specified for a CGL-based OpenGL implementation by setting the attribute CL_CGL_SHAREGROUP_KHR, and the specified share group does not identify a valid CGL share group object (if the cl_khr_gl_sharing extension is enabled).
  • CL_INVALID_OPERATION if the cl_khr_gl_sharing extension is enabled and if a context was specified as described above and any of the following conditions hold:
    • A context or share group object was specified for one of CGL, EGL, GLX, or WGL and the OpenGL implementation does not support that window-system binding API.
    • More than one of the attributes CL_CGL_SHAREGROUP_KHR, CL_EGL_DISPLAY_KHR, CL_GLX_DISPLAY_KHR, and CL_WGL_HDC_KHR is set to a non-default value.
    • Both of the attributes CL_CGL_SHAREGROUP_KHR and CL_GL_CONTEXT_KHR are set to non-default values.
    • Any of the devices specified in the devices argument cannot support OpenCL objects which share the data store of an OpenGL object, as described in section 9.7.
  • CL_INVALID_DX9_MEDIA_ADAPTER_KHR if the media adapter specified for interoperability is not compatible with the devices against which the context is to be created (only if the cl_khr_dx9_media_sharing extension is supported).
  • CL_INVALID_ADAPTER_KHR if any of the values of the properties CL_CONTEXT_ADAPTER_D3D9_KHR, CL_CONTEXT_ADAPTER_D3D9EX_KHR or CL_CONTEXT_ADAPTER_DXVA_KHR is non-NULL and does not specify a valid media adapter with which the cl_device_ids against which this context is to be created may interoperate (only if the cl_khr_dx9_media_sharing extension is supported).
  • CL_INVALID_OPERATION if interoperability is specified by setting CL_CONTEXT_ADAPTER_D3D9_KHR, CL_CONTEXT_ADAPTER_D3D9EX_KHR or CL_CONTEXT_ADAPTER_DXVA_KHR to a non-NULL value, and interoperability with another graphics API is also specified (only if the cl_khr_dx9_media_sharing extension is supported).
  • CL_INVALID_OPERATION if Direct3D 11 interoperability is specified by setting CL_INVALID_D3D11_DEVICE_KHR to a non-NULL value, and interoperability with another graphics API is also specified (only if the cl_khr_d3d11_sharing extension is supported).
  • CL_INVALID_D3D11_DEVICE_KHR if the value of the property CL_CONTEXT_D3D11_DEVICE_KHR is non-NULL and does not specify a valid Direct3D 11 device with which the cl_device_ids against which this context is to be created may interoperate (only if the cl_khr_d3d11_sharing extension is supported).
  • CL_INVALID_D3D11_DEVICE_KHR if the Direct3D 11 device specified for interoperability is not compatible with the devices against which the context is to be created (only if the cl_khr_d3d11_sharing extension is supported).

Specification

OpenCL Specification

Also see

clGetDeviceIDs, clCreateContextFromType, clRetainContext, clReleaseContext, clGetContextInfo

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