Typing ctrl c ctrl z causes the shell to send a

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Unformatted text preview: r("waitpid error"); printf("Handler reaped child %d\n", (int)pid); Sleep(2); return; } int main() { int i, n; char buf[MAXBUF]; if (signal(SIGCHLD, handler1) == SIG_ERR) unix_error("signal error"); /* parent creates children */ for (i = 0; i < 3; i++) { if (Fork() == 0) { printf("Hello from child %d\n", (int)getpid()); Sleep(1); exit(0); } } /* parent waits for terminal input and then processes it */ if ((n = read(STDIN_FILENO, buf, sizeof(buf))) < 0) unix_error("read"); printf("Parent processing input\n"); while (1) ; exit(0); } code/ecf/signal1.c Figure 8.28: signal1: This program is flawed because it fails to deal with the facts that signals can block, signals are not queued, and system calls can be interrupted. 432 <ctrl-z> Suspended linux> ps PID TTY STAT TIME COMMAND ... 10319 p5 T 0:03 signal1 10321 p5 Z 0:00 (signal1 <zombie>) 10323 p5 R 0:00 ps CHAPTER 8. EXCEPTIONAL CONTROL FLOW What went wrong? The problem is that our code failed to account for the facts that signals can block and that signals are not queued. Here’s what happened: The first signal is received and caught by the parent. While the handler is still processing the first signal, the second signal is delivered and added to the set of pending signals. However, s...
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This note was uploaded on 09/02/2010 for the course ELECTRICAL 360 taught by Professor Schultz during the Spring '10 term at BYU.

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