Design and Implementation of an Efficient I/O Method for a Real-Time User Level Thread Library

We have developed a portable user-level thread library RT-PTL on UNIX, which is intended to be used for soft realtime processings, such as multimedia systems. A user-level thread is known to be more efficient than a kernel-level one because of its small context switch overhead. However, user-level thread has a restriction that if one thread issues a system call that forces the calling process to be entirely blocked (such as disk I/O operation), no other thread is runnable until the system call has completed. This characteristic is undesirable for real-time processing. In this article, we have shown a method to overcome this restriction. Using this method, if one thread requests a system call such as disk I/O operation, only the thread that issues the request is blocked and other threads can continue execution. We have implemented this method and have confirmed by some experiments that the method is widely usable and is also efficient.