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diff --git a/mit-pthreads/NOTES b/mit-pthreads/NOTES deleted file mode 100644 index cebdc6a396c..00000000000 --- a/mit-pthreads/NOTES +++ /dev/null @@ -1,59 +0,0 @@ - -Here are some notes on the internals of the implementation. - -LIBC routines. - - Unfortuanately many of the libc routine return a pointer to static data. -There are two methods to deal with this. One write a new routine where the -arguments are different, and have one argument be a pointer to some space -to store the data, or two use thread specific data and warn the user that -data isn't valid if the calling thread is terminated. - -INTERNAL LOCKING -To prevent deadlocks the following rules were used for locks. - -1. Local locks for mutex queues and other like things are only locked - by running threads, at NO time will a local lock be held by - a thread in a non running state. -2. Only threads that are in a run state can attempt to lock another thread, - this way, we can assume that the lock will be released shortly, and don't - have to unlock the local lock. -3. The only time a thread will have a pthread->lock and is not in a run - state is when it is in the reschedule routine. -4. The reschedule routine assumes all local locks have been released, - there is a lock on the currently running thread (pthread_run), - and that this thread is being rescheduled to a non running state. - It is safe to unlock the currently running threads lock after it - has been rescheduled. -5. The reschedule routine locks the kernel, sets the state of the currently - running thread, unlocks the currently running thread, calls the - context switch routines. -6 the kernel lock is used only ... - - -7. The order of locking is ... - -1 local locks -2 pthread->lock /* Assumes it will get it soon */ -3 pthread_run->lock /* Assumes it will get it soon, but must release 2 */ -4 kernel lock /* Currently assumes it will ALWAYS get it. */ - -8. The kernel lock will be changed to a spin lock for systems that -already support kernel threads, this way we can mutiplex threads onto -kernel threads. -9. There are points where the kernel is locked and it needs to get -either a local lock or a pthread lock, if at these points the code -fails to get the lock the kernel gives up and sets a flag which will -be checked at a later point. -10. Interrupts are dissabled while the kernel is locked, the interrupt -mask must be checked afterwards or cleared in some way, after interrputs -have been reenabled, this allows back to back interrupts, but should always -avoid missing one. - ------------------------------------------------------------------------------- -Copyright (c) 1994 Chris Provenzano. All rights reserved. -This product includes software developed by the Univeristy of California, -Berkeley and its contributors. - -For further licencing and distribution restrictions see the file COPYRIGHT -included in this directory. |