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Remzi Arpaci-Dusseau
2018-04-04 13:42:13 -05:00
parent dbecc97f4f
commit 2413114247
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concurrency-xv6-threads/README.md
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@@ -16,22 +16,22 @@ library, with a `thread_create()` call and `lock_acquire()` and
Your new clone system call should look like this: `int
clone(void(*fcn)(void*), void *arg1, void *arg2, void *stack)`. This call
creates a new kernel thread which shares the calling process's address
space. File descriptors are copied as in fork. The new process uses `stack` as
its user stack, which is passed two arguments (`arg1` and `arg2`) and uses a
fake return PC (`0xffffffff`); a proper thread will simply call `exit()` when
it is done (and not `return`). The stack should be one page in size and
page-aligned. The new thread starts executing at the address specified by
`fcn`. As with `fork()`, the PID of the new thread is returned to the parent
(for simplicity, threads each have their own process ID).
space. File descriptors are copied as in `fork()`. The new process uses
`stack` as its user stack, which is passed two arguments (`arg1` and `arg2`)
and uses a fake return PC (`0xffffffff`); a proper thread will simply call
`exit()` when it is done (and not `return`). The stack should be one page in
size and page-aligned. The new thread starts executing at the address
specified by `fcn`. As with `fork()`, the PID of the new thread is returned to
the parent (for simplicity, threads each have their own process ID).
The other new system call is int `join(void **stack)`. This call waits for a
The other new system call is `int join(void **stack)`. This call waits for a
child thread that shares the address space with the calling process to
exit. It returns the PID of waited-for child or -1 if none. The location of
the child's user stack is copied into the argument `stack` (which can then be
freed).
You also need to think about the semantics of a couple of existing system
calls. For example, int `wait()` should wait for a child process that does not
calls. For example, `int wait()` should wait for a child process that does not
share the address space with this process. It should also free the address
space if this is last reference to it. Also, `exit()` should work as before
but for both processes and threads; little change is required here.