paul solomon - Page 70 - Developer IT

How to use pipes for nonblocking IPC (UART emulation)

- by codebauer

I would like to write some test/emulation code that emulates a serial port connection. The real code looks like this: DUT <- UART - testtool.exe My plan is to use create a test application (CodeUnderTest.out) on linux that forks to launch testool.out with two (read & write) named pipes as arguments. But I cannot figure out how to make all the pipe IO non-blocking! The setup would look like this:. CodeUnderTest.out <- named pipes - testTool.out (lauched from CodeUnderTest.out) I have tried opening the pipes as following: open(wpipe,O_WRONLY|O_NONBLOCK); open(rpipe,O_RDONLY|O_NONBLOCK); But the write blocks until the reader opens the wpipe. Next I tried the following: open(wpipe,O_RDWR|O_NONBLOCK); open(rpipe,O_RDONLY|O_NONBLOCK); But then the reader of the first message never gets any data (doesn't block though) I also tried adding open and close calls around each message, but that didn't work either... Here is some test code: #include <stdio.h> #include <sys/types.h> #include <unistd.h> #include <fcntl.h> pid_t pid; char* rpipe, *wpipe,*x; FILE *rh,*wh; int rfd,wfd; void openrpipe( void ) { rfd = open(rpipe,O_RDONLY|O_NONBLOCK); rh = fdopen(rfd,"rb"); printf("%sopeningr %x\n",x,rh); } void openwpipe( void ) { //Fails when reader not already opened //wfd = open(wpipe,O_WRONLY|O_NONBLOCK); wfd = open(wpipe,O_RDWR|O_NONBLOCK); wh = fdopen(wfd,"wb"); printf("%sopeningw %x\n",x,wh); } void closerpipe( void ) { int i; i = fclose(rh); printf("%sclosingr %d\n",x,i); } void closewpipe( void ) { int i; i = fclose(wh); printf("%sclosingw %d\n",x,i); } void readpipe( char* expect, int len) { char buf[1024]; int i=0; printf("%sreading\n",x); while(i==0) { //printf("."); i = fread(buf,1,len,rh); } printf("%sread (%d) %s\n",x,i,buf); } void writepipe( char* data, int len) { int i,j; printf("%swriting\n",x); i = fwrite(data,1,len,rh); j = fflush(rh); //No help! printf("%sflush %d\n",x,j); printf("%swrite (%d) %s\n",x,i,data); } int main(int argc, char **argv) { rpipe = "readfifo"; wpipe = "writefifo"; x = ""; pid = fork(); if( pid == 0) { wpipe = "readfifo"; rpipe = "writefifo"; x = " "; openrpipe(); openwpipe(); writepipe("paul",4); readpipe("was",3); writepipe("here",4); closerpipe(); closewpipe(); exit(0); } openrpipe(); openwpipe(); readpipe("paul",4); writepipe("was",3); readpipe("here",4); closerpipe(); closewpipe(); return( -1 ); } BTW: To use the testocd above you need to pipes in the cwd: mkfifo ./readfifo mkfifo ./writefifo

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