libfortran/90038 Reap dead children when wait=.false.

When using posix_spawn or fork to launch a child process, the parent
needs to wait for the child, otherwise the dead child is left as a
zombie process. For this purpose one can install a signal handler for
SIGCHLD.

2019-05-19  Janne Blomqvist  <jb@gcc.gnu.org>

	PR libfortran/90038
	* intrinsics/execute_command_line (sigchld_handler): New function.
        (execute_command_line): Install handler for SIGCHLD.
        * configure.ac: Check for presence of sigaction and waitpid.
        * config.h.in: Regenerated.
        * configure: Regenerated.

Regtested on x86_64-pc-linux-gnu.

From-SVN: r271384

libgfortran/ChangeLog

+2019-05-19  Janne Blomqvist  <jb@gcc.gnu.org>
+
+        PR libfortran/90038
+        * intrinsics/execute_command_line (sigchld_handler): New function.
+        (execute_command_line): Install handler for SIGCHLD.
+        * configure.ac: Check for presence of sigaction and waitpid.
+        * config.h.in: Regenerated.
+        * configure: Regenerated.
+
 2019-05-17  Janne Blomqvist  <jb@gcc.gnu.org>
 
 	PR libfortran/90038

libgfortran/config.h.in

@@ -666,6 +666,9 @@
 /* Define to 1 if you have the `setmode' function. */
 #undef HAVE_SETMODE
 
+/* Define to 1 if you have the `sigaction' function. */
+#undef HAVE_SIGACTION
+
 /* Define to 1 if you have the `sin' function. */
 #undef HAVE_SIN
 
@@ -831,6 +834,9 @@
 /* Define to 1 if you have the `vsnprintf' function. */
 #undef HAVE_VSNPRINTF
 
+/* Define to 1 if you have the `waitpid' function. */
+#undef HAVE_WAITPID
+
 /* Define if target has a reliable stat. */
 #undef HAVE_WORKING_STAT
 

libgfortran/configure

@@ -2638,6 +2638,8 @@ as_fn_append ac_func_list " link"
 as_fn_append ac_func_list " symlink"
 as_fn_append ac_func_list " sleep"
 as_fn_append ac_func_list " ttyname"
+as_fn_append ac_func_list " sigaction"
+as_fn_append ac_func_list " waitpid"
 as_fn_append ac_func_list " alarm"
 as_fn_append ac_func_list " access"
 as_fn_append ac_func_list " fork"
@@ -12698,7 +12700,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 12701 "configure"
+#line 12703 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -12804,7 +12806,7 @@ else
   lt_dlunknown=0; lt_dlno_uscore=1; lt_dlneed_uscore=2
   lt_status=$lt_dlunknown
   cat > conftest.$ac_ext <<_LT_EOF
-#line 12807 "configure"
+#line 12809 "configure"
 #include "confdefs.h"
 
 #if HAVE_DLFCN_H
@@ -16976,6 +16978,10 @@ done
 
 
 
+
+
+
+
 fi
 
 # Check strerror_r, cannot be above as versions with two and three arguments exist

libgfortran/configure.ac

@@ -314,7 +314,7 @@ if test "${hardwire_newlib:-0}" -eq 1; then
 else
    AC_CHECK_FUNCS_ONCE(getrusage times mkstemp strtof strtold snprintf \
    ftruncate chsize chdir getentropy getlogin gethostname kill link symlink \
-   sleep ttyname \
+   sleep ttyname sigaction waitpid \
    alarm access fork posix_spawn setmode fcntl writev \
    gettimeofday stat fstat lstat getpwuid vsnprintf dup \
    getcwd localtime_r gmtime_r getpwuid_r ttyname_r clock_gettime \

libgfortran/intrinsics/execute_command_line.c

@@ -36,6 +36,9 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 #include <spawn.h>
 extern char **environ;
 #endif
+#if defined(HAVE_POSIX_SPAWN) || defined(HAVE_FORK)
+#include <signal.h>
+#endif
 
 enum { EXEC_SYNCHRONOUS = -2, EXEC_NOERROR = 0, EXEC_SYSTEMFAILED,
        EXEC_CHILDFAILED, EXEC_INVALIDCOMMAND };
@@ -62,6 +65,14 @@ set_cmdstat (int *cmdstat, int value)
 }
 
 
+#if defined(HAVE_WAITPID) && defined(HAVE_SIGACTION)
+static void
+sigchld_handler (int signum __attribute__((unused)))
+{
+  while (waitpid ((pid_t)(-1), NULL, WNOHANG) > 0) {}
+}
+#endif
+
 static void
 execute_command_line (const char *command, bool wait, int *exitstat,
 		      int *cmdstat, char *cmdmsg,
@@ -82,6 +93,20 @@ execute_command_line (const char *command, bool wait, int *exitstat,
 
       set_cmdstat (cmdstat, EXEC_NOERROR);
 
+#if defined(HAVE_SIGACTION) && defined(HAVE_WAITPID)
+      static bool sig_init_saved;
+      bool sig_init = __atomic_load_n (&sig_init_saved, __ATOMIC_RELAXED);
+      if (!sig_init)
+	{
+	  struct sigaction sa;
+	  sa.sa_handler = &sigchld_handler;
+	  sigemptyset(&sa.sa_mask);
+	  sa.sa_flags = SA_RESTART | SA_NOCLDSTOP;
+	  sigaction(SIGCHLD, &sa, 0);
+	  __atomic_store_n (&sig_init_saved, true, __ATOMIC_RELAXED);
+	}
+#endif
+
 #ifdef HAVE_POSIX_SPAWN
       const char * const argv[] = {"sh", "-c", cmd, NULL};
       if (posix_spawn (&pid, "/bin/sh", NULL, NULL,