libevent build failures with -std=c99

[PHHargrove]

As was noted in issue #17, Linux does not define NSIG unless _USE_MISC is defined.
For this reason, configuration with CC="gcc -std=c99" fails when building libevent because NSIG is undefined in strict C99 mode:

[...]/openmpi-3.0.0rc1/opal/mca/event/libevent2022/libevent/signal.c: In function 'evsig_cb':
[...]/openmpi-3.0.0rc1/opal/mca/event/libevent2022/libevent/signal.c:135:14: error: 'NSIG' undeclared (first use in this function); did you mean '_NSIG'?
  int ncaught[NSIG];
              ^~~~
              _NSIG

Something as simple as the following somewhere in libevent (event-internal.h?) might be sufficient:

#if !defined(NSIG) && defined(_NSIG)
#  define NSIG _NSIG
#endif

However, that alone is not sufficient since there are other things that are outside of strict C99:

[...]/openmpi-3.0.0rc1/opal/mca/event/libevent2022/libevent/signal.c: In function 'opal_libevent2022__evsig_set_handler':
[...]/openmpi-3.0.0rc1/opal/mca/event/libevent2022/libevent/signal.c:214:19: error: storage size of 'sa' isn't known
  struct sigaction sa;
                   ^~

That, at least, is POSIX rather than "MISC".

So, it may be a good idea to document that the embedded libevent is not compatible with (at least) Linux glibc in strict C99 mode.

[rhc54]

Might be interesting to check their 2.1 release and see if it is fixed there

[rhc54]

Well, v2.1.8 certainly doesn't build by default:

sample/event-read-fifo.c: In function ‘main’:
sample/event-read-fifo.c:109:6: warning: implicit declaration of function ‘lstat’ [-Wimplicit-function-declaration]
  if (lstat(fifo, &st) == 0) {
      ^~~~~
sample/event-read-fifo.c:109:2: warning: nested extern declaration of ‘lstat’ [-Wnested-externs]
  if (lstat(fifo, &st) == 0) {
  ^~
sample/event-read-fifo.c:110:21: error: ‘S_IFMT’ undeclared (first use in this function)
   if ((st.st_mode & S_IFMT) == S_IFREG) {
                     ^~~~~~
sample/event-read-fifo.c:110:21: note: each undeclared identifier is reported only once for each function it appears in
sample/event-read-fifo.c:110:32: error: ‘S_IFREG’ undeclared (first use in this function)
   if ((st.st_mode & S_IFMT) == S_IFREG) {
                                ^~~~~~~

Turns out the definition of lstat is covered by:

#if defined __USE_BSD || defined __USE_XOPEN_EXTENDED || defined __USE_XOPEN2K

[jsquyres]

We're not going to make libevent C99 compliant. Closing as "wontfix".

[abeltre1]

We're not going to make libevent C99 compliant. Closing as "wontfix".

I am getting the same problem with version 4.0.0 after I upgraded to the latest gcc. Do you have any immediate solutions?

[jsquyres]

If this is happening to you in v4.0.x, please open a new issue with all the relevant details (logs, etc.). Thanks!