Re: cvs commit: src/lib/libthread_xu Makefile pthread.map src/lib/libthread_xu/arch Makefile.inc src/lib/libthread_xu/arch/alpha Makefile.inc src/lib/libthread_xu/arch/alpha/alpha pthread_md.c src/lib/libthread_xu/arch/alpha/include pthread_md.h src/lib/libthread_xu/arch/amd64 ...

[Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx>]

:The management thread should be avoided, that introduces complex into
:userland, I don't want to go old evil linuxthread way.
:I only need one flag to indicate that the thread now executes in
:kernel(pthread_exit() calls _exit()), so its userland resource is no 
:longer needed, e.g. its userland stack and user thread control block, so 
:other threads can reuse them when creating new thread or recycle it at 
:sometime later, but without this flag, there is always a race condition, 
:it is not safe to reuse it because that thread may be still using the 
:stack, although it called _exit(), but that does not say it is not using 
:the stack! calling _exit() pushes return address on stack, and it 
:destroys another thread's memory if the stack was reused by other 
:threads very quickly.
:In detail, I want following feature:
:a syscall allows userland to set an userland address, for example:
:__sys_set_thread_exit_addr(int *addr), it remembers the addr
:in kernel thread structure, if the thread calls _exit(),
:in kernel, kernel code writes a value to addr, that's the only
:thing I need to do userland garbage collection.
:In this way I can avoid complex of management thread.
:
:Cheers,
:David Xu

    Hmm.  Well, I really dislike adding single-purpose system calls.  If I
    do this we need to try to make the system call a bit more general-purpose.
    For example, we could use it to detect abnormal thread termination as
    well as deal with the stack resource race in the normal thread-exit case.

    So something like this:

    __sys_set_exit_data(int *addr, int data);

    Defined to be:

    "When a process exits the system will store the specified data into the
    specified address.  Only one address may be registered per process.
    The feature can be disabled by passing addr = NULL.

    In an rfork/thread baesd system this may be used to detect abnormal 
    process exits and to synchronize stack resource reuse with normal thread
    termination."

    How's that?

					-Matt
					Matthew Dillon 
					<dillon@xxxxxxxxxxxxx>