cvs commit: src/lib/libthread_xu Makefile src/lib/libthread_xu/arch src/lib/libthread_xu/arch/alpha 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 ...

User Davidxu xuyifeng at
Wed Feb 2 05:58:09 PST 2005

Matthew Dillon wrote:
: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.
: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

    How's that?
This is fine to me, did you consider how to exit whole process not
just a single thread ? right now, I am using _exit(), but it only
exits current thread, other threads can not be shutdown.
					Matthew Dillon 
					<dillon at xxxxxxxxxxxxx>

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