Tuesday, October 25, 2011

abort function in unix

 * abort function in c
abort function causes abnormal program termination

#include <stdlib.h>

void abort(void);

This function never returns

This function sends the SIGABRT signal to the caller. (Processes should not ignore this signal.) ISO C states that calling abort will deliver an unsuccessful termination notification to the host environment by calling raise(SIGABRT).

ISO C requires that if the signal is caught and the signal handler returns, abort still doesn't return to its caller. If this signal is caught, the only way the signal handler can't return is if it calls exit, _exit, _Exit, longjmp, or siglongjmp. (Section 10.15 discusses the differences between longjmp and siglongjmp.) POSIX.1 also specifies that abort overrides the blocking or ignoring of the signal by the process.

The intent of letting the process catch the SIGABRT is to allow it to perform any cleanup that it wants to do before the process terminates. If the process doesn't terminate itself from this signal handler, POSIX.1 states that, when the signal handler returns, abort terminates the process.

The ISO C specification of this function leaves it up to the implementation as to whether output streams are flushed and whether temporary files are deleted. POSIX.1 goes further and requires that if the call to abort terminates the process, then the effect on the open standard I/O streams in the process will be the same as if the process had called fclose on each stream before terminating.

Earlier versions of System V generated the SIGIOT signal from the abort function. Furthermore, it was possible for a process to ignore this signal or to catch it and return from the signal handler, in which case abort returned to its caller.

4.3BSD generated the SIGILL signal. Before doing this, the 4.3BSD function unblocked the signal and reset its disposition to SIG_DFL (terminate with core file). This prevented a process from either ignoring the signal or catching it.

Historically, implementations of abort differ in how they deal with standard I/O streams. For defensive programming and improved portability, if we want standard I/O streams to be flushed, we specifically do it before calling abort.

Since most UNIX System implementations of tmpfile call unlink immediately after creating the file, the ISO C warning about temporary files does not usually concern us.

See Also 
POSIX Signal Tutorial and example codes

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