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<div class="category closed"><a href="../index.html" title="The root of the site.">CUDA Toolkit
v6.5</a></div>
<div class="category"><a href="index.html" title="CUDA Runtime API">CUDA Runtime API</a></div>
<ul>
<li>
<div class="section-link"><a href="api-sync-behavior.html#api-sync-behavior">1. API synchronization behavior </a></div>
</li>
<li>
<div class="section-link"><a href="stream-sync-behavior.html#stream-sync-behavior">2. Stream synchronization behavior</a></div>
</li>
<li>
<div class="section-link"><a href="modules.html#modules">3. Modules</a></div>
<ul>
<li>
<div class="section-link"><a href="group__CUDART__DEVICE.html#group__CUDART__DEVICE">3.1. Device Management</a></div>
</li>
<li>
<div class="section-link"><a href="group__CUDART__THREAD__DEPRECATED.html#group__CUDART__THREAD__DEPRECATED">3.2. Thread Management [DEPRECATED]</a></div>
</li>
<li>
<div class="section-link"><a href="group__CUDART__ERROR.html#group__CUDART__ERROR">3.3. Error Handling</a></div>
</li>
<li>
<div class="section-link"><a href="group__CUDART__STREAM.html#group__CUDART__STREAM">3.4. Stream Management</a></div>
</li>
<li>
<div class="section-link"><a href="group__CUDART__EVENT.html#group__CUDART__EVENT">3.5. Event Management</a></div>
</li>
<li>
<div class="section-link"><a href="group__CUDART__EXECUTION.html#group__CUDART__EXECUTION">3.6. Execution Control</a></div>
</li>
<li>
<div class="section-link"><a href="group__CUDART__OCCUPANCY.html#group__CUDART__OCCUPANCY">3.7. Occupancy</a></div>
</li>
<li>
<div class="section-link"><a href="group__CUDART__MEMORY.html#group__CUDART__MEMORY">3.8. Memory Management</a></div>
</li>
<li>
<div class="section-link"><a href="group__CUDART__UNIFIED.html#group__CUDART__UNIFIED">3.9. Unified Addressing</a></div>
</li>
<li>
<div class="section-link"><a href="group__CUDART__PEER.html#group__CUDART__PEER">3.10. Peer Device Memory Access</a></div>
</li>
<li>
<div class="section-link"><a href="group__CUDART__OPENGL.html#group__CUDART__OPENGL">3.11. OpenGL Interoperability</a></div>
</li>
<li>
<div class="section-link"><a href="group__CUDART__OPENGL__DEPRECATED.html#group__CUDART__OPENGL__DEPRECATED">3.12. OpenGL Interoperability [DEPRECATED]</a></div>
</li>
<li>
<div class="section-link"><a href="group__CUDART__D3D9.html#group__CUDART__D3D9">3.13. Direct3D 9 Interoperability</a></div>
</li>
<li>
<div class="section-link"><a href="group__CUDART__D3D9__DEPRECATED.html#group__CUDART__D3D9__DEPRECATED">3.14. Direct3D 9 Interoperability [DEPRECATED]</a></div>
</li>
<li>
<div class="section-link"><a href="group__CUDART__D3D10.html#group__CUDART__D3D10">3.15. Direct3D 10 Interoperability</a></div>
</li>
<li>
<div class="section-link"><a href="group__CUDART__D3D10__DEPRECATED.html#group__CUDART__D3D10__DEPRECATED">3.16. Direct3D 10 Interoperability [DEPRECATED]</a></div>
</li>
<li>
<div class="section-link"><a href="group__CUDART__D3D11.html#group__CUDART__D3D11">3.17. Direct3D 11 Interoperability</a></div>
</li>
<li>
<div class="section-link"><a href="group__CUDART__D3D11__DEPRECATED.html#group__CUDART__D3D11__DEPRECATED">3.18. Direct3D 11 Interoperability [DEPRECATED]</a></div>
</li>
<li>
<div class="section-link"><a href="group__CUDART__VDPAU.html#group__CUDART__VDPAU">3.19. VDPAU Interoperability</a></div>
</li>
<li>
<div class="section-link"><a href="group__CUDART__INTEROP.html#group__CUDART__INTEROP">3.20. Graphics Interoperability</a></div>
</li>
<li>
<div class="section-link"><a href="group__CUDART__TEXTURE.html#group__CUDART__TEXTURE">3.21. Texture Reference Management</a></div>
</li>
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<div class="section-link"><a href="group__CUDART__SURFACE.html#group__CUDART__SURFACE">3.22. Surface Reference Management</a></div>
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<div class="section-link"><a href="group__CUDART__TEXTURE__OBJECT.html#group__CUDART__TEXTURE__OBJECT">3.23. Texture Object Management</a></div>
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<div class="section-link"><a href="group__CUDART__SURFACE__OBJECT.html#group__CUDART__SURFACE__OBJECT">3.24. Surface Object Management</a></div>
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<div class="section-link"><a href="group__CUDART____VERSION.html#group__CUDART____VERSION">3.25. Version Management</a></div>
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<div class="section-link"><a href="group__CUDART__HIGHLEVEL.html#group__CUDART__HIGHLEVEL">3.26. C++ API Routines</a></div>
</li>
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<div class="section-link"><a href="group__CUDART__DRIVER.html#group__CUDART__DRIVER">3.27. Interactions with the CUDA Driver API</a></div>
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<div class="section-link"><a href="group__CUDART__PROFILER.html#group__CUDART__PROFILER">3.28. Profiler Control</a></div>
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<div class="section-link"><a href="group__CUDART__TYPES.html#group__CUDART__TYPES">3.29. Data types used by CUDA Runtime</a></div>
</li>
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<div class="section-link"><a href="annotated.html#annotated">4. Data Structures</a></div>
<ul>
<li>
<div class="section-link"><a href="class____cudaOccupancyB2DHelper.html#class____cudaOccupancyB2DHelper">4.1. __cudaOccupancyB2DHelper</a></div>
</li>
<li>
<div class="section-link"><a href="structcudaChannelFormatDesc.html#structcudaChannelFormatDesc">4.2. cudaChannelFormatDesc</a></div>
</li>
<li>
<div class="section-link"><a href="structcudaDeviceProp.html#structcudaDeviceProp">4.3. cudaDeviceProp</a></div>
</li>
<li>
<div class="section-link"><a href="structcudaExtent.html#structcudaExtent">4.4. cudaExtent</a></div>
</li>
<li>
<div class="section-link"><a href="structcudaFuncAttributes.html#structcudaFuncAttributes">4.5. cudaFuncAttributes</a></div>
</li>
<li>
<div class="section-link"><a href="structcudaIpcEventHandle__t.html#structcudaIpcEventHandle__t">4.6. cudaIpcEventHandle_t</a></div>
</li>
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<div class="section-link"><a href="structcudaIpcMemHandle__t.html#structcudaIpcMemHandle__t">4.7. cudaIpcMemHandle_t</a></div>
</li>
<li>
<div class="section-link"><a href="structcudaMemcpy3DParms.html#structcudaMemcpy3DParms">4.8. cudaMemcpy3DParms</a></div>
</li>
<li>
<div class="section-link"><a href="structcudaMemcpy3DPeerParms.html#structcudaMemcpy3DPeerParms">4.9. cudaMemcpy3DPeerParms</a></div>
</li>
<li>
<div class="section-link"><a href="structcudaPitchedPtr.html#structcudaPitchedPtr">4.10. cudaPitchedPtr</a></div>
</li>
<li>
<div class="section-link"><a href="structcudaPointerAttributes.html#structcudaPointerAttributes">4.11. cudaPointerAttributes</a></div>
</li>
<li>
<div class="section-link"><a href="structcudaPos.html#structcudaPos">4.12. cudaPos</a></div>
</li>
<li>
<div class="section-link"><a href="structcudaResourceDesc.html#structcudaResourceDesc">4.13. cudaResourceDesc</a></div>
</li>
<li>
<div class="section-link"><a href="structcudaResourceViewDesc.html#structcudaResourceViewDesc">4.14. cudaResourceViewDesc</a></div>
</li>
<li>
<div class="section-link"><a href="structcudaTextureDesc.html#structcudaTextureDesc">4.15. cudaTextureDesc</a></div>
</li>
<li>
<div class="section-link"><a href="structsurfaceReference.html#structsurfaceReference">4.16. surfaceReference</a></div>
</li>
<li>
<div class="section-link"><a href="structtextureReference.html#structtextureReference">4.17. textureReference</a></div>
</li>
</ul>
</li>
<li>
<div class="section-link"><a href="functions.html#functions">5. Data Fields</a></div>
</li>
<li>
<div class="section-link"><a href="deprecated.html#deprecated">6. Deprecated List</a></div>
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<div class="section-link"><a href="notices-header.html#notices-header">Notices</a></div>
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<!-- --></a><h2 class="topictitle2 cppModule">3.27. Interactions with the CUDA Driver API</h2>
<div class="section">
<p>This section describes the interactions between the CUDA Driver API and the CUDA Runtime API</p>
<p class="p apiDesc_subtitle"><strong class="ph b">Primary Contexts</strong></p>
<p class="p">There exists a one to one relationship between CUDA devices in the CUDA Runtime API and CUcontext s in the CUDA Driver API
within a process. The specific context which the CUDA Runtime API uses for a device is called the device's primary context.
From the perspective of the CUDA Runtime API, a device and its primary context are synonymous.
</p>
<p class="p apiDesc_subtitle"><strong class="ph b">Initialization and Tear-Down</strong></p>
<p class="p">CUDA Runtime API calls operate on the CUDA Driver API CUcontext which is current to to the calling host thread.</p>
<p class="p">The function <a class="xref" href="group__CUDART__DEVICE.html#group__CUDART__DEVICE_1g418c299b069c4803bfb7cab4943da383" title="Set device to be used for GPU executions." shape="rect">cudaSetDevice()</a> makes the primary context for the specified device current to the calling thread by calling cuCtxSetCurrent().
</p>
<p class="p">The CUDA Runtime API will automatically initialize the primary context for a device at the first CUDA Runtime API call which
requires an active context. If no CUcontext is current to the calling thread when a CUDA Runtime API call which requires an
active context is made, then the primary context for a device will be selected, made current to the calling thread, and initialized.
</p>
<p class="p">The context which the CUDA Runtime API initializes will be initialized using the parameters specified by the CUDA Runtime
API functions <a class="xref" href="group__CUDART__DEVICE.html#group__CUDART__DEVICE_1g18074e885b4d89f5a0fe1beab589e0c8" title="Sets flags to be used for device executions." shape="rect">cudaSetDeviceFlags()</a>, <a class="xref" href="group__CUDART__D3D9.html#group__CUDART__D3D9_1g3b7a9c5a5f249fa1f8fb5743304474b5" title="Sets the Direct3D 9 device to use for interoperability with a CUDA device." shape="rect">cudaD3D9SetDirect3DDevice()</a>, <a class="xref" href="group__CUDART__D3D10__DEPRECATED.html#group__CUDART__D3D10__DEPRECATED_1geec2934147774dd7a611df971a548675" title="Sets the Direct3D 10 device to use for interoperability with a CUDA device." shape="rect">cudaD3D10SetDirect3DDevice()</a>, <a class="xref" href="group__CUDART__D3D11__DEPRECATED.html#group__CUDART__D3D11__DEPRECATED_1g447d066794c8070432514185d1326446" title="Sets the Direct3D 11 device to use for interoperability with a CUDA device." shape="rect">cudaD3D11SetDirect3DDevice()</a>, <a class="xref" href="group__CUDART__OPENGL__DEPRECATED.html#group__CUDART__OPENGL__DEPRECATED_1gc6502eba2a85a3f222dc960de8df8115" title="Sets a CUDA device to use OpenGL interoperability." shape="rect">cudaGLSetGLDevice()</a>, and <a class="xref" href="group__CUDART__VDPAU.html#group__CUDART__VDPAU_1g93a9727b90c526a3493918bceafcb3f7" title="Sets a CUDA device to use VDPAU interoperability." shape="rect">cudaVDPAUSetVDPAUDevice()</a>. Note that these functions will fail with <a class="xref" href="group__CUDART__TYPES.html#group__CUDART__TYPES_1gg3f51e3575c2178246db0a94a430e0038a906ddf08d574274bf7334adb1497550" shape="rect">cudaErrorSetOnActiveProcess</a> if they are called when the primary context for the specified device has already been initialized. (or if the current device
has already been initialized, in the case of <a class="xref" href="group__CUDART__DEVICE.html#group__CUDART__DEVICE_1g18074e885b4d89f5a0fe1beab589e0c8" title="Sets flags to be used for device executions." shape="rect">cudaSetDeviceFlags()</a>).
</p>
<p class="p">Primary contexts will remain active until they are explicitly deinitialized using <a class="xref" href="group__CUDART__DEVICE.html#group__CUDART__DEVICE_1gdcc2c6f914eb9461565b12648faa5e28" title="Destroy all allocations and reset all state on the current device in the current process." shape="rect">cudaDeviceReset()</a>. The function <a class="xref" href="group__CUDART__DEVICE.html#group__CUDART__DEVICE_1gdcc2c6f914eb9461565b12648faa5e28" title="Destroy all allocations and reset all state on the current device in the current process." shape="rect">cudaDeviceReset()</a> will deinitialize the primary context for the calling thread's current device immediately. The context will remain current
to all of the threads that it was current to. The next CUDA Runtime API call on any thread which requires an active context
will trigger the reinitialization of that device's primary context.
</p>
<p class="p">Note that there is no reference counting of the primary context's lifetime. It is recommended that the primary context not
be deinitialized except just before exit or to recover from an unspecified launch failure.
</p>
<p class="p apiDesc_subtitle"><strong class="ph b">Context Interoperability</strong></p>
<p class="p">Note that the use of multiple CUcontext s per device within a single process will substantially degrade performance and is
strongly discouraged. Instead, it is highly recommended that the implicit one-to-one device-to-context mapping for the process
provided by the CUDA Runtime API be used.
</p>
<p class="p">If a non-primary CUcontext created by the CUDA Driver API is current to a thread then the CUDA Runtime API calls to that thread
will operate on that CUcontext, with some exceptions listed below. Interoperability between data types is discussed in the
following sections.
</p>
<p class="p">The function <a class="xref" href="group__CUDART__UNIFIED.html#group__CUDART__UNIFIED_1gab5cad40942fd554556035741d3fe5a2" title="Returns attributes about a specified pointer." shape="rect">cudaPointerGetAttributes()</a> will return the error <a class="xref" href="group__CUDART__TYPES.html#group__CUDART__TYPES_1gg3f51e3575c2178246db0a94a430e0038bfc1b14096f31fc7b43c08397af90856" shape="rect">cudaErrorIncompatibleDriverContext</a> if the pointer being queried was allocated by a non-primary context. The function <a class="xref" href="group__CUDART__PEER.html#group__CUDART__PEER_1g9e5ea65a18938c2b8715a5602105c306" title="Enables direct access to memory allocations on a peer device." shape="rect">cudaDeviceEnablePeerAccess()</a> and the rest of the peer access API may not be called when a non-primary CUcontext is current. To use the pointer query and
peer access APIs with a context created using the CUDA Driver API, it is necessary that the CUDA Driver API be used to access
these features.
</p>
<p class="p">All CUDA Runtime API state (e.g, global variables' addresses and values) travels with its underlying CUcontext. In particular,
if a CUcontext is moved from one thread to another then all CUDA Runtime API state will move to that thread as well.
</p>
<p class="p">Please note that attaching to legacy contexts (those with a version of 3010 as returned by cuCtxGetApiVersion()) is not possible.
The CUDA Runtime will return <a class="xref" href="group__CUDART__TYPES.html#group__CUDART__TYPES_1gg3f51e3575c2178246db0a94a430e0038bfc1b14096f31fc7b43c08397af90856" shape="rect">cudaErrorIncompatibleDriverContext</a> in such cases.
</p>
<p class="p apiDesc_subtitle"><strong class="ph b">Interactions between CUstream and cudaStream_t</strong></p>
<p class="p">The types CUstream and <a class="xref" href="group__CUDART__TYPES.html#group__CUDART__TYPES_1ge15d9c8b7a240312b533d6122558085a" shape="rect">cudaStream_t</a> are identical and may be used interchangeably.
</p>
<p class="p apiDesc_subtitle"><strong class="ph b">Interactions between CUevent and cudaEvent_t</strong></p>
<p class="p">The types CUevent and <a class="xref" href="group__CUDART__TYPES.html#group__CUDART__TYPES_1gea2f543a9fc0e52fe4ae712920fd1247" shape="rect">cudaEvent_t</a> are identical and may be used interchangeably.
</p>
<p class="p apiDesc_subtitle"><strong class="ph b">Interactions between CUarray and cudaArray_t</strong></p>
<p class="p">The types CUarray and struct cudaArray * represent the same data type and may be used interchangeably by casting the two types
between each other.
</p>
<p class="p">In order to use a CUarray in a CUDA Runtime API function which takes a struct cudaArray *, it is necessary to explicitly cast
the CUarray to a struct cudaArray *.
</p>
<p class="p">In order to use a struct cudaArray * in a CUDA Driver API function which takes a CUarray, it is necessary to explicitly cast
the struct cudaArray * to a CUarray .
</p>
<p class="p apiDesc_subtitle"><strong class="ph b">Interactions between CUgraphicsResource and cudaGraphicsResource_t</strong></p>
<p class="p">The types CUgraphicsResource and <a class="xref" href="group__CUDART__TYPES.html#group__CUDART__TYPES_1gf58dd8d3c7a65714ff7f5459adbf7e6f" shape="rect">cudaGraphicsResource_t</a> represent the same data type and may be used interchangeably by casting the two types between each other.
</p>
<p class="p">In order to use a CUgraphicsResource in a CUDA Runtime API function which takes a <a class="xref" href="group__CUDART__TYPES.html#group__CUDART__TYPES_1gf58dd8d3c7a65714ff7f5459adbf7e6f" shape="rect">cudaGraphicsResource_t</a>, it is necessary to explicitly cast the CUgraphicsResource to a <a class="xref" href="group__CUDART__TYPES.html#group__CUDART__TYPES_1gf58dd8d3c7a65714ff7f5459adbf7e6f" shape="rect">cudaGraphicsResource_t</a>.
</p>
<p class="p">In order to use a <a class="xref" href="group__CUDART__TYPES.html#group__CUDART__TYPES_1gf58dd8d3c7a65714ff7f5459adbf7e6f" shape="rect">cudaGraphicsResource_t</a> in a CUDA Driver API function which takes a CUgraphicsResource, it is necessary to explicitly cast the <a class="xref" href="group__CUDART__TYPES.html#group__CUDART__TYPES_1gf58dd8d3c7a65714ff7f5459adbf7e6f" shape="rect">cudaGraphicsResource_t</a> to a CUgraphicsResource.
</p>
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