cl_khr_command_buffer_multi_device clEnqueueCommandBufferKHR clarification

Hi,

We have a few questions regarding clEnqueueCommandBufferKHR when multiple command queues are passed to it:

1- When does the event state transition happens?

We understand the status is set to CL_COMPLETE when the workload finishes across all command queues. What about CL_RUNNING and CL_SUBMITTED?

> [CL_SUBMITTED](https://registry.khronos.org/OpenCL/specs/3.0-unified/html/OpenCL_API.html#CL_SUBMITTED): The initial state for all user events. For all other events, indicates that the command has been submitted by the host to the device.

> [CL_RUNNING](https://registry.khronos.org/OpenCL/specs/3.0-unified/html/OpenCL_API.html#CL_RUNNING): Indicates that the device has started executing this command. In order for the execution status of an enqueued command to change from [CL_SUBMITTED](https://registry.khronos.org/OpenCL/specs/3.0-unified/html/OpenCL_API.html#CL_SUBMITTED) to [CL_RUNNING](https://registry.khronos.org/OpenCL/specs/3.0-unified/html/OpenCL_API.html#CL_RUNNING), all events that this command is waiting on must have completed successfully i.e. their execution status must be [CL_COMPLETE](https://registry.khronos.org/OpenCL/specs/3.0-unified/html/OpenCL_API.html#CL_COMPLETE).

These states are with respect to the device the command is running on, but in this case we might have multiple devices. Would we have the following?

CL_SUBMITTED means command buffer has been submitted into all the queues.
CL_RUNNING means started running into all the queues.

2- Does clFlush/clFinish need to be called for all command queues in the command buffer when calling clEnqueueCommandBufferKHR?

Scenario A:

```
// A list of in-order command queues
cl_command_queue queues[num_queues];
// Create the command buffer for multiple command queues, record some commands across all queues and finalize it
// Assume no sync points when recording.
cl_command_buffer_khr command_buffer = clCreateCommandBufferKHR(num_queues, queues, ...);
...
clEnqueueCommandBuffer(0, NULL, command_buffer, 0, NULL, NULL);
clEnqueueNDRangeKernel(queues[0], some_kernel, ..., 0, NULL, NULL);
clFinish(queues[0]);
```

In this case, does clEnqueueNDRangeKernel execute because it only waits on the commands from queues[0], or does the code hang because it needs all queues to have finished to continue?

Thank you.

Start by reading the linked OpenCL API definitions for CL_SUBMITTED and CL_RUNNING, then review the command-buffer multi-device semantics relevant to clEnqueueCommandBufferKHR, clFlush, and clFinish. Done means the event-state transitions and required queue synchronization behavior are resolved and documented unambiguously.

Written by the indexing model from the issue text.