Hi there,
at the moment implementing a mark and sweep garbage collection
subsystem is quite a hack, because you always have to use up
some signals for suspend/resume all threads to implement this.
For runtime environments (like D system libraries or JVMs) this is
a hack, since you take away flexibility from the application.
A possible solution would be a syscall or a PTRACE extension
to realize the suspend/resume. I best describe the possible
syscall manpages here, so you get an idea.
NAME
suspend_other - suspends execution of all but the calling thread
SYNOPSIS
long suspend_other(void);
RETURN VALUE
Positive count suspended threads on success.
If 0, then suspend_other was a no-op and there is nothing to resume, but the
call should still considered successful.
If the number is -1, the errno has to be checked for possible error values.
ERRORS
EDEADLK We run already a suspend_other() and the calling thread
has just been resumed.
EPERM The calling thread is not allowed to do this.
(optional case due to security)
DESCRIPTION
After sucessful return of this call, the affected process
is single threaded and only the calling thread runs
in this process (==MM struct).
The thread, which calls this is responsible for resuming
all the suspended threads. One can iterate through
"/proc/self/task/", to verify for sure that one knows all threads,
if the returned count doesn't match the expected value.
Any per thread queued signals are deferred until resume_other()
or process destruction.
NOTES
This call might be restricted to the main thread.
------------
NAME
resume_other - resume execution of foreign thread in this process
SYNOPSIS
long resume_other(pid_t tid)
RETURN VALUE
Returns 0, if successful.
Otherwise -1 is returned, the errno has to be checked for
possible error values and the call has no effect at all.
Any non-blocked signals of that thread which happend during
suspend/resume are deliverd now.
ERRORS
EINVAL The thread is running already.
(this is a severe caller BUG).
ESRCH The thread with tid does not exist.
(or doesn't belong to this process).
EPERM The calling thread is not allowed to do this.
(optional case due to security)
DESCRIPTION
After sucessful return of this call, the affected thread
is the the state it was before it was suspended
by calling suspend_other().
NOTES
The value -1 for tid is reserved for future extension
(e.g. meaning ALL other threads).
This call might be restricted to the main thread.
---------
Any opinions?
Best Regards
Ingo Oeser
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