Re: Detect that a child is waiting for input
On 24/11/16 17:58, unDEFER wrote: But really it is not decision.. The program stops not because where is no input, but because there is other process reading terminal.. It is not that I need.. You can write a wrapper program (let's call it wrp). Wrp can redirect your program's input though itself, and play with the session foreground based on whether there is input pending or not. This way, your program will stop if the combination of two things happen: 1. It is waiting for input and 2. There is none This is, I think, what you want.
Re: Detect that a child is waiting for input
The program which stops even run without "&":
#!/usr/bin/rdmd
import std.stdio;
import std.file;
import std.string;
import core.sys.posix.unistd;
import core.stdc.errno;
import core.stdc.string;
void main()
{
int res = core.sys.posix.unistd.tcsetpgrp(0, getppid());
if (res != 0)
{
writefln("tcsetpgrp error: %s",
fromStringz(strerror(errno)).idup());
return;
}
foreach (line; stdin.byLine)
{
writefln(line);
}
}
But really it is not decision.. The program stops not because
where is no input, but because there is other process reading
terminal..
It is not that I need..
Re: Detect that a child is waiting for input
You can detect whether another process received a signal by ptracing it. If you are only ptracing for signals, then the performance penalty shouldn't be too severe. Shachar On 24/11/16 12:35, unDEFER wrote: On Wednesday, 23 November 2016 at 07:18:27 UTC, Shachar Shemesh wrote: The shell does that for background processes. I think it takes away the TTY from its children, and this way, when they try to read from stdin, they get SIGSTOP from the system. I'm not sure what the precise mechanism is. There are flags passed to wait which will cause it to report when a child gets SIGSTOP. Hope this helps, Shachar So, I have found with strace, this signal is SIGTTIN is special signal which sends to _background_ task when it tries to read from terminal. So it is possible such detect when I will write not simple pipeProcess, but will write terminal emulator. Thank you.
Re: Detect that a child is waiting for input
Here is good information about difference between foreground process groups and background: https://www.win.tue.nl/~aeb/linux/lk/lk-10.html Shortly, there is only one process group which is foreground, you can get it with tcgetpgrp(fd) or set it with tcsetpgrp(fd,pgrp). To setup process group of the process use setpgid(pid, pgid);
Re: Detect that a child is waiting for input
On Wednesday, 23 November 2016 at 07:18:27 UTC, Shachar Shemesh wrote: The shell does that for background processes. I think it takes away the TTY from its children, and this way, when they try to read from stdin, they get SIGSTOP from the system. I'm not sure what the precise mechanism is. There are flags passed to wait which will cause it to report when a child gets SIGSTOP. Hope this helps, Shachar So, I have found with strace, this signal is SIGTTIN is special signal which sends to _background_ task when it tries to read from terminal. So it is possible such detect when I will write not simple pipeProcess, but will write terminal emulator. Thank you.
Re: Detect that a child is waiting for input
On Wednesday, 23 November 2016 at 20:02:08 UTC, wobbles wrote: You could wait for some period of time - and if that's passed and the child hasn't printed anything you can assume it's waiting for input. Yes, I also have thought about it, thank you.
Re: Detect that a child is waiting for input
On Wednesday, 23 November 2016 at 15:54:30 UTC, unDEFER wrote: On Tuesday, 22 November 2016 at 22:30:06 UTC, wobbles wrote: Easier said than done as there's no signal the child sends to say "OK, I'm waiting now". You can use expect to do this, if you know what the output of the child will be just before it's waiting for IO. This is the D lib I've written to do this: https://github.com/grogancolin/dexpect It's not wonderful or anything, but it works :) Thank you, good decision. Maybe I will use the idea. But how to detect that "cat" (without arguments) waits input, if it nothing prints? You dont :) You could wait for some period of time - and if that's passed and the child hasn't printed anything you can assume it's waiting for input.
Re: Detect that a child is waiting for input
On Wednesday, 23 November 2016 at 07:18:27 UTC, Shachar Shemesh wrote: The shell does that for background processes. I think it takes away the TTY from its children, and this way, when they try to read from stdin, they get SIGSTOP from the system. I'm not sure what the precise mechanism is. There are flags passed to wait which will cause it to report when a child gets SIGSTOP. Hope this helps, Shachar Really interesting information, thank you, I will try to dig in this direction.
Re: Detect that a child is waiting for input
On Tuesday, 22 November 2016 at 22:30:06 UTC, wobbles wrote: Easier said than done as there's no signal the child sends to say "OK, I'm waiting now". You can use expect to do this, if you know what the output of the child will be just before it's waiting for IO. This is the D lib I've written to do this: https://github.com/grogancolin/dexpect It's not wonderful or anything, but it works :) Thank you, good decision. Maybe I will use the idea. But how to detect that "cat" (without arguments) waits input, if it nothing prints?
Re: Detect that a child is waiting for input
On 20/11/16 14:21, unDEFER wrote: Hello! I'm using pipeProcess() to create a process: pipes = pipeProcess(["bash", "-c", BASH_COMMAND], Redirect.stdin | Redirect.stdout | Redirect.stderr); Is it possible detect that the child is waiting for input on stdin? I can't find decision even for C. I think it is impossible if the child uses unblocking reading. But I want to detect blocking reading. The shell does that for background processes. I think it takes away the TTY from its children, and this way, when they try to read from stdin, they get SIGSTOP from the system. I'm not sure what the precise mechanism is. There are flags passed to wait which will cause it to report when a child gets SIGSTOP. Hope this helps, Shachar
Re: Detect that a child is waiting for input
On Monday, 21 November 2016 at 07:29:55 UTC, unDEFER wrote: On Sunday, 20 November 2016 at 21:03:57 UTC, John Colvin wrote: If blocking is an error, you could close stdin and assuming the process checks the error codes correctly No, I mean blocking is not error. One method to find it, run gdb or strace and see where the process stopped, or which syscall was last. But I believe that must be other way. Easier said than done as there's no signal the child sends to say "OK, I'm waiting now". You can use expect to do this, if you know what the output of the child will be just before it's waiting for IO. This is the D lib I've written to do this: https://github.com/grogancolin/dexpect It's not wonderful or anything, but it works :)
Re: Detect that a child is waiting for input
On Sunday, 20 November 2016 at 21:03:57 UTC, John Colvin wrote: If blocking is an error, you could close stdin and assuming the process checks the error codes correctly No, I mean blocking is not error. One method to find it, run gdb or strace and see where the process stopped, or which syscall was last. But I believe that must be other way.
Re: Detect that a child is waiting for input
On Sunday, 20 November 2016 at 12:21:19 UTC, unDEFER wrote: Hello! I'm using pipeProcess() to create a process: pipes = pipeProcess(["bash", "-c", BASH_COMMAND], Redirect.stdin | Redirect.stdout | Redirect.stderr); Is it possible detect that the child is waiting for input on stdin? I can't find decision even for C. I think it is impossible if the child uses unblocking reading. But I want to detect blocking reading. If blocking is an error, you could close stdin and assuming the process checks the error codes correctly
