main() { unsigned int status; $DESCRIPTOR(ttname,"TT:"); static long long time;
/* Assign a channel to a device */ status = SYS$ASSIGN( &ttname, /* devnam - device name */ &ttchan, /* chan - channel number */ 0, /* acmode - access mode */ 0, /* mbxnam - logical name for mailbox */ 0 ); /* flags */ if (!$VMS_STATUS_SUCCESS(status)) LIB$SIGNAL(status);
status = sys$qiow(efn,ttchan,IO$_SENSEMODE|IO$M_TYPEAHDCNT,0, 0,0, 0,0,0,0,0,0); printf("Yes have to read\n"); status = sys$qiow(efn,ttchan,IO$_TTYREADALL|IO$M_NOECHO|IO$M_TRMNOECHO,&iosb, 0,0, &vkbuff,sizeof(vkbuff),0,0,0,0);
I just read about M_TYPEAHDCNT it returns a number of characters in the buffer and GET A FIRST CHARCTER from the buffer. This is the not thing I need. Do not any character should be read. I'll read the buffer from another place of the program.
static char buf[1000]; int efn=32; unsigned short ttchan;
main() { unsigned int status; $DESCRIPTOR(ttname,"TT:"); static long long time;
/* Assign a channel to a device */ status = SYS$ASSIGN( &ttname, /* devnam - device name */ &ttchan, /* chan - channel number */ 0, /* acmode - access mode */ 0, /* mbxnam - logical name for mailbox */ 0 ); /* flags */ if (!$VMS_STATUS_SUCCESS(status)) LIB$SIGNAL(status); printf ("sleeping for a second or two. Type something.\n"); sleep(2); status = sys$qiow(efn,ttchan,IO$_SENSEMODE|IO$M_TYPEAHDCNT,&iosb, 0,0, &vkbuff,0,0,0,0,0); printf ("read ahead count = %d, First char = %c\n", vkbuff.number, vkbuff.first); printf("Yes have to read\n"); status = sys$qiow(efn,ttchan,IO$_TTYREADALL|IO$M_NOECHO|IO$M_TRMNOECHO,&iosb, 0,0, buf,sizeof(buf),0,0,0,0); printf ("%s\n", buf); // sloppy. return SS$_NORMAL; }
$ run READAHEAD sleeping for a second or two. Type something. read ahead count = 20, First char = s Yes have to read sdgfsrtghsdtrghdtrgh $ Exit
My normal approach to this class of problem (on terminals, mailboxes, and other devices) is to use the AST facility.
Polling in any way is not the best of practices when an event-based alternative exists (e.g., ASTs).
For an introduction to ASTs, see the various manuals. My DECUS presentation "Introduction to OpenVMS AST Programming" can be found at http://www.rlgsc.com/cets/2000/435.html
main() { $DESCRIPTOR(term_dsc,"SYS$INPUT:"); char user_prmpt[50]="User Name :"; char passw_prmpt[50]="User Password :"; unsigned int status; unsigned short chan,iosb[4]; char username[50]; char passw[50];
memset(passw,0,50); memset(username,0,50); status = sys$assign(&term_dsc,&chan,0,0,0); status = sys$qiow(0,chan,IO$_READPROMPT,iosb,0,0,username,49,0,0,user_prmpt,strlen(user_prmpt)); username[iosb[1]] = '\0'; status = sys$qiow(0,chan,IO$_READPROMPT|IO$M_NOECHO,iosb,0,0,passw,49,0,0,passw_prmpt,strlen(passw_prmpt)); passw[iosb[1]] = '\0'; printf("\n\nYour User Name : %s \nPassword : %s\n",username,passw);
This question implies a program design which suffers two flaws.
The first is polling - you sit in a loop checking at intervals if there's anything to do. The tradeoff is, a shorter period reduces the latency in processing, but increases the time wasted spinning in the loop when there's nothing to do.
The second is the model of checking to see if there's something to do before doing it, with inherent timing windows if you "just miss" the event you're waiting for.
In OpenVMS program design, polling is rarely necessary or desirable. You can use asynchronous code to detect and act on events only when necessary and immediately after they occur.
Change your design from:
loop IF event has occured THEN ProcessEvent wait polling interval endloop
to
When event occurs ProcessEvent
In its simplest form, issue a $QIO (no W) when READVBLK specifying an AST routine to execute when the I/O completes.
In an AST design, typically the main program sets up the first AST for each thread of events then goes to sleep. As each AST fires it resets itself for the thread to continue.
>> If the ...IO$_SENSEMODE|IO$M_TYPEAHDCNT ... be able to sleep while nothing to read
Ah, now I understand your question better. I was only answering the first question
>> I'm need to check if terminal have something to read.
That's exactly what the sensemode does but not what you want, nor as others pointed out what you want to use as it leads to polling algorithms.
>> Mailbox driver has a good IO$M_READATTN
Yes, that warn but takes no action. This is not available in the terminal driver. The closest thing is the OUTBAND setmode, but that initiated with selected control characters. Not generic.
And I suppose you could issue a 1 byte read with AST, but then that byte will be in the buffer. That becomes awkward quickly.
You'll probably want to create a wrappers to be able to give a 'read_terminal' routine which does not actually do a qio, but returns the data from a qio which already completed.
You can decide whether the program processes each read completely before issuing the next, or just keeps on reading fulling multiple buffers if need be.
As John indicated it is often handy to use SYS$DCLAST to get the show rolling. Probably passing control block parameter with IOSB and buffer and whatever else is handy to keep all context pointed to in one parameter.
The IOSB is needed if you do fancy terminator handling.... but for anything fancy yo may want to look at SMG or similar.
If that's the actual C code being tested, consider adding return status and IOSB status checks into the C code.
Status checks are a defensive coding technique that often helps track the triggers of errors, and can provide an effective means of avoiding a application stackdump when something gets tangled and trips on an earlier and unhandled error within the application.
Also consider moving away from hard-coding a static EFN (and particularly not using an EF that the lib$get_ef call "owns" and can pass out) and moving to an allocated event flag or (for something akin to this case) to ENF$C_ENF "don't care" event flag, too.
