Advanced Programming in the UNIX® Environment

ptg10805159

Section 10.6 Reentrant Functions 331

abort faccessat linkat select socketpair

accept fchmod listen sem_post stat

access fchmodat lseek send symlink

aio_error fchown lstat sendmsg symlinkat

aio_return fchownat mkdir sendto tcdrain

aio_suspend fcntl mkdirat setgid tcflow

alarm fdatasync mkfifo setpgid tcflush

bind fexecve mkfifoat setsid tcgetattr

cfgetispeed fork mknod setsockopt tcgetpgrp

cfgetospeed fstat mknodat setuid tcsendbreak

cfsetispeed fstatat open shutdown tcsetattr

cfsetospeed fsync openat sigaction tcsetpgrp

chdir ftruncate pause sigaddset time

chmod futimens pipe sigdelset timer_getoverrun

chown getegid poll sigemptyset timer_gettime

clock_gettime geteuid posix_trace_event sigfillset timer_settime

close getgid pselect sigismember times

connect getgroups raise signal umask

creat getpeername read sigpause uname

dup getpgrp readlink sigpending unlink

dup2 getpid readlinkat sigprocmask unlinkat

execl getppid recv sigqueue utime

execle getsockname recvfrom sigset utimensat

execv getsockopt recvmsg sigsuspend utimes

execve getuid rename sleep wait

_Exit kill renameat sockatmark waitpid

_exit link rmdir socket write

Figure 10.4Reentrant functions that may be called from a signal handler

stored inmain.Therefore, as a general rule, when calling the functions listed in

Figure10.4 from a signal handler, we should save and restoreerrno.(Be awarethat a

commonly caught signal isSIGCHLD,and its signal handler usually calls one of the

waitfunctions. All thewaitfunctions can changeerrno.)

Note thatlongjmp(Section 7.10) andsiglongjmp(Section 10.15) aremissing

from Figure10.4, because the signal may have occurred while the main routine was

updating a data structure in a nonreentrant way.This data structurecould be left half

updated if we callsiglongjmpinstead of returning from the signal handler.If it is

going to do such things as update global data structures, as we describe here, while

catching signals that causesigsetjmpto be executed, an application needs to block the

signals while updating the data structures.

Example

Figure10.5 shows a program that calls the nonreentrant functiongetpwnamfrom a

signal handler that is called every second. We describe the alarm function in

Section 10.10.We use it here to generate aSIGALRMsignal every second.