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The real reasons in this case is (1) it is inappropriate, and (2) it is incompatible with the PROTECTED and KERNEL builds where pthreads cannot be supported.

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The KERNEL build, on the other hand, uses a Memory Management Unit (MMU) to create a virtual address space which in which there is still a separate protected kernel address space, but many user address spaces for user programs. These are usually called processes. This is the familiar build model that you find with high-end Unix-like systems such as Linux.

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• Part of this is getting all user interfaces out of the OS.
• Another part is migrating all pthread support out of operating system and into the user-facing C library.
• An additional objective on the roadmap is to streamline the kernel threads and to disconnect them from task groups.  Kernel threads should not be part of any task group.

From Apache NuttX Issue 1108 in In regard to this last point, the following is taken from Apache NuttX Issue 1108: "Remove streams from Kernel Threads":

No Streams in Kernel Threads

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