1 files changed, 51 insertions, 0 deletions
diff --git a/src/libposixplz/doublefork.c b/src/libposixplz/doublefork.c
new file mode 100644
index 0000000..6038a9f
--- /dev/null
+++ b/src/libposixplz/doublefork.c
@@ -0,0 +1,51 @@
+/* ISC license. */
+
+#include <sys/wait.h>
+#include <unistd.h>
+#include <errno.h>
+#include <skalibs/uint64.h>
+#include <skalibs/allreadwrite.h>
+#include <skalibs/djbunix.h>
+#include <skalibs/posixplz.h>
+
+pid_t doublefork ()
+{
+  char pack[8] ;
+  int fd[2] ;
+  pid_t child ;
+  if (pipe(fd) == -1) return -1 ;
+  child = fork() ;
+  switch (child)
+  {
+    case -1:
+    {
+      fd_close(fd[1]) ;
+      fd_close(fd[0]) ;
+      return -1 ;
+    }
+    case 0:
+    {
+      pid_t pid ;
+      fd_close(fd[0]) ;
+      pid = fork() ;
+      switch (pid)
+      {
+        case -1: _exit(errno) ;
+        case 0: fd_close(fd[1]) ; return 0 ;
+      }
+      uint64_pack_big(pack, pid) ;
+      _exit((allwrite(fd[1], pack, 8) < 8) ? errno : 0) ;
+    }
+  }
+  fd_close(fd[1]) ;
+  {
+    uint64_t grandchild = 0 ;
+    int wstat ;
+    if (allread(fd[0], pack, 8) < 8) grandchild = 1 ;
+    fd_close(fd[0]) ;
+    wait_pid(child, &wstat) ;
+    if (grandchild) return (errno = WIFSIGNALED(wstat) ? EINTR : WEXITSTATUS(wstat), -1) ;
+    uint64_unpack_big(pack, &grandchild) ;
+    return (pid_t)grandchild ;
+  }
+}