C-Threads -- user-level threads for Mach
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This user thread package contains 6 calls for the thread management (create, exit, join, detach, yield and self).
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Similarly to the DCE package, C-Threads offer mutexes and conditional variables for synchronization. Their semantics and syntax is also very similar to the DCE threads.
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C-Threads had many different implementations on Mach. It has been ported to other Operating Systems too. We briefly inspect two implementation based on the Mach kernel thread support:
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In the first implementation, C-Threads were managed entirely in the user space. For each C-Thread process, there was one Mach kernel thread. This solution suffered from a known problem -- blocking the whole process on a blocking operation called by one thread.
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A second approach, mapped 1-to-1 all C-Threads onto Mach kernel threads. The threads were then scheduled preemptively, taking advantage of the multiprocessor hardware.
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