Advanced Programming in the UNIX® Environment

ptg10805159

Section 10.17 abortFunction 365

We test each of the global flags beforecallingreadand again ifreadreturns an

interrupted system call error.The problem occurs if either signal is caught between the

first twoifstatements and the subsequent call toread.Signals occurring in hereare

lost, as indicated by the code comment. The signal handlers arecalled, and they set the

appropriate global variable, but thereadnever returns (unless some data is ready to be

read).

What we would like to be able to do is the following sequence of steps, in order.

1. BlockSIGINTandSIGALRM.


2. Test the two global variables to see whether either signal has occurred and, if so,
   handle the condition.


3. Callread(or any other system function) and unblock the two signals, as an
   atomic operation.

Thesigsuspendfunction helps us only if step 3 is apauseoperation.

10.17 abortFunction

We mentioned earlier that theabortfunction causes abnormal program termination.

#include <stdlib.h>

void abort(void);

This function never returns

This function sends theSIGABRTsignal to the caller.(Processes should not ignorethis

signal.) ISOCstates that calling abortwill deliver an unsuccessful termination

notification to the host environment by callingraise(SIGABRT).

ISO C requires that if the signal is caught and the signal handler returns,abortstill

doesn’t return to its caller.Ifthis signal is caught, the only way the signal handler can’t

return is if it callsexit,_exit,_Exit, longjmp,orsiglongjmp.(Section 10.15

discusses the differences betweenlongjmpandsiglongjmp.) POSIX.1 also specifies

thatabortoverrides the blocking or ignoring of the signal by the process.

The intent of letting the process catch theSIGABRTis to allow it to perform any

cleanup that it wants to do beforethe process terminates. If the process doesn’t

terminate itself from this signal handler,POSIX.1 states that, when the signal handler

returns,abortterminates the process.

The ISO C specification of this function leaves it up to the implementation as to

whether output streams areflushed and whether temporary files (Section 5.13) are

deleted. POSIX.1 goes further and allows an implementation to callfcloseon open

standardI/O streams beforeterminating if the call toabortterminates the process.

Earlier versions of System V generated theSIGIOTsignal from the abortfunction.

Furthermore, it was possible for a process to ignorethis signal or to catch it and return from

the signal handler, in which caseabortreturned to its caller.