lush@EE.MsState.Edu (Edward Luke) (09/26/90)
In signal.h there is a signal defined as: #define SIGIO 23 /* input/output possible signal */ I have an application that will be doing computations, asynchronously with this I would like to get a signal when new data arrives on an input file descriptor, or when an output file descriptor is free to be filled again. Is it possible for me to do this without using fork() to start another process to monitor the file descriptor? Can I tell the OS to give me a SIGIO when there is a pending condition on a socket? Just what is the SIGIO signal for? Edward Luke Mississippi State University NSF Engineering Research Center for Complex Field Simulations
jik@athena.mit.edu (Jonathan I. Kamens) (09/27/90)
In article <LUSH.90Sep26102017@athena0.EE.MsState.Edu>, lush@EE.MsState.Edu (Edward Luke) writes: |> I would like to get a signal when new data arrives on an |> input file descriptor, or when an output file descriptor is free to be |> filled again. Is it possible for me to do this without using fork() |> to start another process to monitor the file descriptor? Can I tell |> the OS to give me a SIGIO when there is a pending condition on a |> socket? Just what is the SIGIO signal for? See the man page fcntl(2). You want to use the F_SETOWN fcntl call on the file descriptor and set the ownership to your PID, and then use the FASYNC fcntl to turn on asynchronous I/O; when ASYNC is enabled, and input comes in on the file descriptor, your process will get SIGIO. I'm not certain that you'll get SIGIO if there is room for writing in a pipe; I've never used it for that, and fcntl(2) only mentions data waiting to be read when it mentions FASYNC, so I don't know whether or not it'll work. Oh, you'll also get SIGURG when there is an "urgent condition" on a socket; I'm not completely sure what an "urgent condition" is, perhaps that's what they call a premature closing of the other end of the socket or something. One more thing -- I believe that if the other end of the FD is closed, you'll get a SIGIO, and then when you read, you'll get 0 bytes, thus signalling EOF. -- Jonathan Kamens USnail: MIT Project Athena 11 Ashford Terrace jik@Athena.MIT.EDU Allston, MA 02134 Office: 617-253-8495 Home: 617-782-0710
symon@aesop.cs.unc.edu (James Symon) (09/27/90)
In article <LUSH.90Sep26102017@athena0.EE.MsState.Edu>, lush@EE.MsState.Edu (Edward Luke) writes: > > In signal.h there is a signal defined as: > #define SIGIO 23 /* input/output possible signal */ > > > I have an application that will be doing computations, asynchronously > with this I would like to get a signal when new data arrives on an > input file descriptor, or when an output file descriptor is free to be > filled again. Is it possible for me to do this without using fork() > to start another process to monitor the file descriptor? Can I tell > the OS to give me a SIGIO when there is a pending condition on a > socket? Just what is the SIGIO signal for? > Here are some little test programs I wrote using standard input (the keyboard) to learn how to do signal trapping. I don't think you need to mess with fcntl(). **************************************** #include <stdio.h> #include <signal.h> int done = 0; void handler(signal) int signal; { if(signal != SIGIO) { printf("caught signal other than SIGIO . . . wrong!"); exit(1); } else { printf("I lied. I'm taking a nap. You'll have to wait.\n"); done = 1; } } main() { extern void handler(); int ndx; signal(SIGIO,handler); while(!done) { printf("I'll do some work here while I wait for your <CR>.\n"); sleep(5); } } ************* Here's another: ************* #include <stdio.h> #include <signal.h> void handler(signal) int signal; { } main() { extern void handler(); int ndx, smask, oldmask; struct sigvec holder; holder.sv_handler = handler; holder.sv_mask = 0; holder.sv_flags = 0; sigvec(SIGIO,&holder,0); smask = sigmask(SIGIO); for(ndx=0; ndx < 4; ndx++) { oldmask = sigblock(smask); printf("smask = %x, oldmask = %x, wait, I'm working . . .\n",smask,oldmask); sleep(1); printf("Well? Hit return.\n"); sigpause(oldmask); sigsetmask(oldmask); } } **************************************************** Jim Symon symon@radonc.unc.edu (919) 966-7710
rembo@unisoft.UUCP (Tony Rems) (09/28/90)
In article <LUSH.90Sep26102017@athena0.EE.MsState.Edu> lush@EE.MsState.Edu (Edward Luke) writes: > >In signal.h there is a signal defined as: >#define SIGIO 23 /* input/output possible signal */ > > >I have an application that will be doing computations, asynchronously >with this I would like to get a signal when new data arrives on an >input file descriptor, or when an output file descriptor is free to be >filled again. Is it possible for me to do this without using fork() >to start another process to monitor the file descriptor? Can I tell >the OS to give me a SIGIO when there is a pending condition on a >socket? Just what is the SIGIO signal for? > Try the select(2) system call on BSD or SVR4 or the poll(2) system call on any SVR3 or greater and this should do what you want. -Tony ----------------------------------------------------- Somedays, it doesn't pay to get out of bed. NOTE: My opinions are barely my own much less my employers'. -----------------------------------------------------
joel@isc.intel.com (Joel Clark) (09/28/90)
In article <1990Sep26.184409.10155@athena.mit.edu> jik@athena.mit.edu (Jonathan I. Kamens) writes: >In article <LUSH.90Sep26102017@athena0.EE.MsState.Edu>, lush@EE.MsState.Edu (Edward Luke) writes: >|> I would like to get a signal when new data arrives on an >|> input file descriptor, or when an output file descriptor is free to be >|> filled again. Is it possible for me to do this without using fork() >|> Just what is the SIGIO signal for? > > See the man page fcntl(2). You want to use the F_SETOWN fcntl call on the >..... > Oh, you'll also get SIGURG when there is an "urgent condition" on a socket; ^^^^^^^^^^^^^^^^ >I'm not completely sure what an "urgent condition" is, perhaps that's what >they call a premature closing of the other end of the socket or something. >-- >Jonathan Kamens USnail: >MIT Project Athena 11 Ashford Terrace >jik@Athena.MIT.EDU Allston, MA 02134 >Office: 617-253-8495 Home: 617-782-0710 An "urgent condition" is when Out Of Band data arrives. This is data sent with the MSG_OOB flag set. i.e. "send(fd,buf,buflen,MSG_OOB)" This is generally used to send signals such as interrupt when a DEL key is hit. Thus the receiving process can handle the SIGURG signal by reading and tossing all the data in the socket upto the MSG_OOB data if this is what it needs to do. Joel Clark Intel Scientific Computers joel@isc.intel.com line fodder
jik@athena.mit.edu (Jonathan I. Kamens) (09/28/90)
In article <16329@thorin.cs.unc.edu>, symon@aesop.cs.unc.edu (James Symon) writes: |> Here are some little test programs I wrote using standard input (the |> keyboard) to learn how to do signal trapping. I don't think you need |> to mess with fcntl(). Your program doesn't work for me unless I add the fcntl I mentioned in my last message. In particular, if I compile the program at the end of this message without DO_ASYNC defined, then it doesn't detect input, but if I compile it with DO_ASYNC defined, then it does. Just because it works without the fcntl on your system, doesn't mean you should expect it to work that way on other systems. Note, too, that if you do the fcntl once on your tty and then forget to turn it off, the next time you run a program that tries to use SIGIO, it'll work even if it doesn't do the fcntl, since the FASYNC will stay in effect on the tty line. -- Jonathan Kamens USnail: MIT Project Athena 11 Ashford Terrace jik@Athena.MIT.EDU Allston, MA 02134 Office: 617-253-8495 Home: 617-782-0710 ------------------------------------------------------------------ #include <stdio.h> #include <signal.h> #include <fcntl.h> #ifdef DO_ASYNC int ttyflags; #endif void handler(signal) int signal; { printf("Got some input.\n"); } void inthandler(signal) int signal; { if (signal) printf("Got an interrupt.\n"); #ifdef DO_ASYNC if (fcntl(fileno(stdin), F_SETFL, ttyflags & ~FASYNC) < 0) { perror("Couldn't set tty flags"); exit(1); } #endif exit(0); } main() { extern void handler(); int ndx, smask, oldmask; struct sigvec holder; #ifdef DO_ASYNC if ((ttyflags = fcntl(fileno(stdin), F_GETFL, 0)) < 0) { perror("Couldn't get tty flags"); exit(1); } if (fcntl(fileno(stdin), F_SETFL, ttyflags | FASYNC) < 0) { perror("Couldn't set tty flags"); exit(1); } #endif holder.sv_handler = (int(*)()) handler; holder.sv_mask = 0; holder.sv_flags = 0; sigvec(SIGIO,&holder,0); holder.sv_handler = (int(*)()) inthandler; holder.sv_mask = 0; holder.sv_flags = 0; sigvec(SIGINT, &holder, 0); smask = sigmask(SIGIO); for(ndx=0; ndx < 4; ndx++) { oldmask = sigblock(smask); printf("smask = %x, oldmask = %x, wait, I'm working . . .\n",smask,oldmask); sleep(1); printf("Well? Hit return.\n"); sigpause(oldmask); sigsetmask(oldmask); } inthandler(0); /* to turn off strange modes */ exit(0); }