Design
NPTL uses a similar approach to LinuxThreads, in that the primary abstraction known by the kernel is still a process, and new threads are created with the clone system call (called from the NPTL library). However, NPTL requires specialized kernel support to implement (for example) the contended case of synchronisation primitives which might require threads to sleep and wake again. The primitive used for this is known as a futex.
NPTL is a so-called 1×1 threads library, in that threads created by the user (via the pthread_create library function) are in 1-1 correspondence with schedulable entities in the kernel (tasks, in the Linux case). This is the simplest possible threading implementation.
An alternative to NPTL's 1×1 model is the m×n model.
Read more about this topic: Native POSIX Thread Library
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