Why does SIGPIPE exist?
From my understanding, SIGPIPE can only occur as the result of a write(), which can (and does) return -1 and set errno to EPIPE<
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Machine info:
Linux 3.2.0-53-generic #81-Ubuntu SMP Thu Aug 22 21:01:03 UTC 2013 x86_64 x86_64 x86_64 GNU/Linux
gcc version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5)
I wrote this code below:
// Writes characters to stdout in an infinite loop, also counts // the number of characters generated and prints them in sighandler // writestdout.c # include# include # include # include int writeCount = 0; void sighandler(int sig) { char buf1[30] ; sprintf(buf1,"signal %d writeCount %d\n", sig, writeCount); ssize_t leng = strlen(buf1); write(2, buf1, leng); _exit(1); } int main() { int i = 0; char buf[2] = "a"; struct sigaction ss; ss.sa_handler = sighandler; sigaction(13, &ss, NULL); while(1) { /* if (writeCount == 4) { write(2, "4th char\n", 10); } */ ssize_t c = write(1, buf, 1); writeCount++; } }
// Reads only 3 characters from stdin and exits // readstdin.c # include# include int main() { ssize_t n ; char a[5]; n = read(0, a, 3); printf("read %zd bytes\n", n); return(0); }
Output:
$ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 11486 $ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 429 $ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 281 $ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 490 $ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 433 $ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 318 $ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 468 $ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 11866 $ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 496 $ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 284 $ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 271 $ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 416 $ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 11268 $ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 427 $ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 8812 $ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 394 $ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 10937 $ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 10931 $ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 3554 $ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 499 $ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 283 $ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 11133 $ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 451 $ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 493 $ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 233 $ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 11397 $ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 492 $ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 547 $ ./writestdout | ./readstdin read 3 bytes signal 13 writeCount 441You can see that in every instance
SIGPIPEis only received after more than 3 characters are (tried to be) written by the writing process.Does this not prove that
SIGPIPEis not generated immediately after reading process terminates but after an attempt to write some more data to a closed pipe?
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