wait for particular process pid
in [Unix Programming]
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From: Jonathan de Boyne Pollard on 8 Apr 2010 18:37 > > > On Windows I would call OpenPorocess to get the process handle and > then use WaitForSingleObject to wait on the handle. I wonder why UNIX > does not have something similar? > Because the Win32 API took advantage of the second system effect. The world gradually learned over the years that handle-based APIs are good things, especially because they eliminate all sorts of race conditions that open up security holes and cause other problems. But the POSIX API has evolved towards this from non-handle-based paradigms in some areas, at varying rates in various parts of the API. It still hasn't fully arrived. So whilst there are various non-portable ways to control processes through handle-based APIs, that vary across systems such as Linux, Solaris, the BSDs, and Plan 9, the portable, POSIX, API still only supports waiting on (and otherwise controlling) processes by their IDs, and even then only waiting on process IDs of direct child processes. There are more reasons for such restrictions today than there were decades ago, in fact. Notice that in recent (2.6.24 and later) versions of Linux with certain features enabled, one cannot even necessarily name all processes on a system by PID from within an arbitrary non-parent process, because they might be in a different, non-contained, PID namespace.
From: Barry Margolin on 8 Apr 2010 22:05
In article <82755qFp8jU8(a)mid.individual.net>, Ian Collins <ian-news(a)hotmail.com> wrote: > On 04/ 9/10 10:21 AM, Ersek, Laszlo wrote: > > On Fri, 9 Apr 2010, Ian Collins wrote: > > > >> On 04/ 9/10 03:02 AM, Rainer Weikusat wrote: > >>> Sasha<agalkin(a)audible.com> writes: > >>> > >>> [...] > >>> > >>>> I need to wait for already running process to track when it exits. I > >>>> know how to do this for the child process spawned by the watcher > >>>> process, I need now to do the same for the process already running. > >>> > >>> "man ptrace" > >> > >> Do some platforms extend ptrace to control non-child processes? > > > > Absolutely; you can attach gdb to an already running, unrelated process. > > > OK, thanks. The online Linux man page > (http://linux.die.net/man/2/ptrace) was a little ambiguous: > > "The ptrace() system call provides a means by which a parent process may > observe and control the execution of another process" > > Note the use of parent and another rather parent and child. Read down to PTRACE_ATTACH: PTRACE_ATTACH Attaches to the process specified in pid, making it a traced "child" of the current process; the behavior of the child is as if it had done a PTRACE_TRACEME. The current process actually becomes the parent of the child process for most purposes (e.g., it will receive notification of child events and appears in ps(1) output as the child's parent), but a getppid(2) by the child will still return the PID of the original parent. -- Barry Margolin, barmar(a)alum.mit.edu Arlington, MA *** PLEASE post questions in newsgroups, not directly to me *** *** PLEASE don't copy me on replies, I'll read them in the group *** |