Date: Sat, 10 Mar 2007 07:15:32 -0800 From: Julian Elischer <julian@elischer.org> To: Tijl Coosemans <tijl@ulyssis.org> Cc: Daniel Eischen <deischen@freebsd.org>, gerald@freebsd.org, freebsd-threads@freebsd.org Subject: Re: signalling remote threads Message-ID: <45F2CB94.6070805@elischer.org> In-Reply-To: <200703101231.16407.tijl@ulyssis.org> References: <200703091515.27133.tijl@ulyssis.org> <200703092100.12199.tijl@ulyssis.org> <45F1DD68.8040103@elischer.org> <200703101231.16407.tijl@ulyssis.org>
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Tijl Coosemans wrote: > On Friday 09 March 2007 23:19, Julian Elischer wrote: >> Tijl Coosemans wrote: >>> On Friday 09 March 2007 18:18, Daniel Eischen wrote: >>>> On Fri, 9 Mar 2007, Tijl Coosemans wrote: >>>>> Is it somehow possible to send a signal to a specific thread in >>>>> another process similar to the linux tkill and tgkill syscalls? >>>>> >>>>> I've seen the thr_kill call that takes an lwpid as argument, but >>>>> it can't send a signal to another process can it? >>>> No, it is not possible and it shouldn't be possible >>>> as it's not portable. From outside the process, you >>>> can send a signal to another _process_ (which will >>>> be delivered to one of its threads depending on >>>> their signal masks), but not to a specific thread >>>> in another process. >>> Ok, thanks. The reason I asked is because Wine uses this to let the >>> wineserver process (windows kernel) send signals to threads in a >>> wine process. >>> >>> The only solution I see then is to have some sort of service thread >>> in the receiving process to dispatch the signal. That would be a >>> portable solution, but lots of work... >> How does something external to a process identify a thread within >> the process? > > Wineserver plays the role of the windows kernel (more or less). It > knows about all the (win32) threads in every wine process. Whenever > a wine process creates a new thread it sends the thread id to the > wineserver. On FreeBSD this is currently always -1. On Linux it is > obtained with gettid(). This id is then later used with tgkill(). > >> And even if you could tell the threads appart, ho do you know which >> one to signal? > > Wineserver handles IPC calls (read: syscalls) from wine processes. > An example where wineserver sends a signal to a specific threads is > when some thread requests to suspend another thread. > >> There is no portable way to identify threads in another process. >> There is also no guarantee that the tread is even externally >> visible. Take the example of a multiplexed threading library (such >> as libc_r) which multiplexes all the threads onto a single user >> process/thread. you basiclly HAVE to ask an agent within the process >> to signal the right thread for you on such a system. If they are >> doing things like that then they are basically writing for only >> Linux. > > So, in case of wineserver and wine, the (only?) portable way would be > for wineserver to know all the pthread_self() identifiers, which can > then be used in an IPC call to an agent in the wine process, that in > turn uses pthread_kill()? basically that would, at least be portable. It would be possible to do it (siggnal it directly) in libpthread if it were running in system_scope mode, (libprhtread can run in 2 modes) and it would be possible to do it if you linked with libthr too though I don't knwo all the details.
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