1 files changed, 154 insertions, 0 deletions
diff --git a/src/lib/process/waitpid.c b/src/lib/process/waitpid.c
new file mode 100644
index 0000000000..9b626394d2
--- /dev/null
+++ b/src/lib/process/waitpid.c
@@ -0,0 +1,154 @@
+/* Copyright (c) 2003-2004, Roger Dingledine
+ * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
+ * Copyright (c) 2007-2019, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file waitpid.c
+ * \brief Convenience structures for handlers for handling waitpid().
+ **/
+
+#include "orconfig.h"
+
+#ifndef _WIN32
+
+#include "lib/process/waitpid.h"
+#include "lib/log/log.h"
+#include "lib/log/util_bug.h"
+#include "lib/malloc/malloc.h"
+#include "ht.h"
+
+#ifdef HAVE_SYS_WAIT_H
+#include <sys/wait.h>
+#endif
+
+#include <string.h>
+
+/* ================================================== */
+/* Convenience structures for handlers for waitpid().
+ *
+ * The tor_process_monitor*() code above doesn't use them, since it is for
+ * monitoring a non-child process.
+ */
+
+/** Mapping from a PID to a userfn/userdata pair. */
+struct waitpid_callback_t {
+  HT_ENTRY(waitpid_callback_t) node;
+  pid_t pid;
+
+  void (*userfn)(int, void *userdata);
+  void *userdata;
+
+  unsigned running;
+};
+
+static inline unsigned int
+process_map_entry_hash_(const waitpid_callback_t *ent)
+{
+  return (unsigned) ent->pid;
+}
+
+static inline unsigned int
+process_map_entries_eq_(const waitpid_callback_t *a,
+                        const waitpid_callback_t *b)
+{
+  return a->pid == b->pid;
+}
+
+static HT_HEAD(process_map, waitpid_callback_t) process_map = HT_INITIALIZER();
+
+HT_PROTOTYPE(process_map, waitpid_callback_t, node, process_map_entry_hash_,
+             process_map_entries_eq_)
+HT_GENERATE2(process_map, waitpid_callback_t, node, process_map_entry_hash_,
+             process_map_entries_eq_, 0.6, tor_reallocarray_, tor_free_)
+
+/**
+ * Begin monitoring the child pid <b>pid</b> to see if we get a SIGCHLD for
+ * it.  If we eventually do, call <b>fn</b>, passing it the exit status (as
+ * yielded by waitpid) and the pointer <b>arg</b>.
+ *
+ * To cancel this, or clean up after it has triggered, call
+ * clear_waitpid_callback().
+ */
+waitpid_callback_t *
+set_waitpid_callback(pid_t pid, void (*fn)(int, void *), void *arg)
+{
+  waitpid_callback_t *old_ent;
+  waitpid_callback_t *ent = tor_malloc_zero(sizeof(waitpid_callback_t));
+  ent->pid = pid;
+  ent->userfn = fn;
+  ent->userdata = arg;
+  ent->running = 1;
+
+  old_ent = HT_REPLACE(process_map, &process_map, ent);
+  if (old_ent) {
+    log_warn(LD_BUG, "Replaced a waitpid monitor on pid %u. That should be "
+             "impossible.", (unsigned) pid);
+    old_ent->running = 0;
+  }
+
+  return ent;
+}
+
+/**
+ * Cancel a waitpid_callback_t, or clean up after one has triggered. Releases
+ * all storage held by <b>ent</b>.
+ */
+void
+clear_waitpid_callback(waitpid_callback_t *ent)
+{
+  waitpid_callback_t *old_ent;
+  if (ent == NULL)
+    return;
+
+  if (ent->running) {
+    old_ent = HT_REMOVE(process_map, &process_map, ent);
+    if (old_ent != ent) {
+      log_warn(LD_BUG, "Couldn't remove waitpid monitor for pid %u.",
+               (unsigned) ent->pid);
+      return;
+    }
+  }
+
+  tor_free(ent);
+}
+
+/** Helper: find the callack for <b>pid</b>; if there is one, run it,
+ * reporting the exit status as <b>status</b>. */
+static void
+notify_waitpid_callback_by_pid(pid_t pid, int status)
+{
+  waitpid_callback_t search, *ent;
+
+  search.pid = pid;
+  ent = HT_REMOVE(process_map, &process_map, &search);
+  if (!ent || !ent->running) {
+    log_info(LD_GENERAL, "Child process %u has exited; no callback was "
+             "registered", (unsigned)pid);
+    return;
+  }
+
+  log_info(LD_GENERAL, "Child process %u has exited; running callback.",
+           (unsigned)pid);
+
+  ent->running = 0;
+  ent->userfn(status, ent->userdata);
+}
+
+/** Use waitpid() to wait for all children that have exited, and invoke any
+ * callbacks registered for them. */
+void
+notify_pending_waitpid_callbacks(void)
+{
+  /* I was going to call this function reap_zombie_children(), but
+   * that makes it sound way more exciting than it really is. */
+  pid_t child;
+  int status = 0;
+
+  while ((child = waitpid(-1, &status, WNOHANG)) > 0) {
+    notify_waitpid_callback_by_pid(child, status);
+    status = 0; /* should be needless */
+  }
+}
+
+#endif /* !defined(_WIN32) */