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In order for Solaris to execute a program in parallel on many processors, the program needs to be written as a collection of functions, each of which is executed by a thread dynamically created in a process. Although the time required for thread creation is faster than process creation, it takes a few mili-seconds for EusLisp to start off a thread after allocating stacks and setting a page attribute for detecting stack-overflow. Since this delay, which should be compared to a function invocation, is intolerable, sufficient number of threads are created by the make-thread function beforehand and put in the system's thread pool, eliminating the need for system calls at evaluation time. Each thread in the thread pool is represented by a thread object, as depicted in Fig.7, consisted of thread-id, several semaphores for synchronization, and slots for argument and evaluation result transfer.
Figure 7: Thread-object for transferring control and data between threads (left) and the collection of threads put in the thread-pool.