support: Add support_process_state_wait

It allows parent process to wait for child state using a polling
strategy over procfs on Linux.  The polling is used over ptrace to
avoid the need to handle signals on the target pid and to handle some
system specific limitation (such as YAMA).

The polling has some limitations, such as resource consumption due
the procfs read in a loop and the lack of synchronization after the
state is obtained.

The interface idea is to simplify some sleep synchronization waitid
tests and is to reduce timeouts by replacing arbitrary waits.

1 files changed, 92 insertions, 0 deletions

diff --git a/support/support_process_state.c b/support/support_process_state.c
new file mode 100644
index 0000000000..76dc798728
--- /dev/null
+++ b/support/support_process_state.c
@@ -0,0 +1,92 @@
+/* Wait for process state.
+   Copyright (C) 2020 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <https://www.gnu.org/licenses/>.  */
+
+#include <stdlib.h>
+#include <time.h>
+#include <string.h>
+
+#include <array_length.h>
+
+#include <support/process_state.h>
+#include <support/xstdio.h>
+#include <support/check.h>
+
+void
+support_process_state_wait (pid_t pid, enum support_process_state state)
+{
+#ifdef __linux__
+  /* For Linux it does a polling check on /proc/<pid>/status checking on
+     third field.  */
+
+  /* It mimics the kernel states from fs/proc/array.c  */
+  static const struct process_states
+  {
+    enum support_process_state s;
+    char v;
+  } process_states[] = {
+    { support_process_state_running,      'R' },
+    { support_process_state_sleeping,     'S' },
+    { support_process_state_disk_sleep,   'D' },
+    { support_process_state_stopped,      'T' },
+    { support_process_state_tracing_stop, 't' },
+    { support_process_state_dead,         'X' },
+    { support_process_state_zombie,       'Z' },
+    { support_process_state_parked,       'P' },
+  };
+
+  char spath[sizeof ("/proc/" + 3) * sizeof (pid_t) + sizeof ("/status") + 1];
+  snprintf (spath, sizeof (spath), "/proc/%i/status", pid);
+
+  FILE *fstatus = xfopen (spath, "r");
+  char *line = NULL;
+  size_t linesiz = 0;
+
+  for (;;)
+    {
+      char cur_state = -1;
+      while (xgetline (&line, &linesiz, fstatus) != -1)
+	if (strncmp (line, "State:", strlen ("State:")) == 0)
+	  {
+	    TEST_COMPARE (sscanf (line, "%*s %c", &cur_state), 1);
+	    break;
+	  }
+      /* Fallback to nanosleep for invalid state.  */
+      if (cur_state == -1)
+	break;
+
+      for (size_t i = 0; i < array_length (process_states); ++i)
+	if (state & process_states[i].s && cur_state == process_states[i].v)
+	  {
+	    free (line);
+	    xfclose (fstatus);
+	    return;
+	  }
+
+      rewind (fstatus);
+      fflush (fstatus);
+
+      if (nanosleep (&(struct timespec) { 0, 10000000 }, NULL) != 0)
+	FAIL_EXIT1 ("nanosleep: %m");
+    }
+
+  free (line);
+  xfclose (fstatus);
+  /* Fallback to nanosleep if an invalid state is found.  */
+#endif
+  nanosleep (&(struct timespec) { 2, 0 }, NULL);
+}