Merge branch 'bug8746_v2_squashed'

Conflicts:
	src/common/include.am

changes/bug8746

@@ -0,0 +1,4 @@
+  o Major bugfixes:
+    - When managing pluggable transports, use OS notification facilities to
+      learn if they have crashed, and do not attempt to kill any process
+      that has already exited. Fix for bug 8746; bugfix on 0.2.3.6-alpha.

configure.ac

@@ -367,6 +367,7 @@ AC_CHECK_FUNCS(
         sysconf \
 	sysctl \
         uname \
+        usleep \
         vasprintf \
 	_vscprintf
 )
@@ -898,6 +899,7 @@ AC_CHECK_HEADERS(
         sys/param.h \
         sys/prctl.h \
         sys/resource.h \
+        sys/select.h \
         sys/socket.h \
 	sys/sysctl.h \
         sys/syslimits.h \

src/common/compat.c

@@ -114,6 +114,12 @@
 /* Only use the linux prctl;  the IRIX prctl is totally different */
 #include <sys/prctl.h>
 #endif
+#ifdef TOR_UNIT_TESTS
+#if !defined(HAVE_USLEEP) && defined(HAVE_SYS_SELECT_H)
+/* as fallback implementation for tor_sleep_msec */
+#include <sys/select.h>
+#endif
+#endif
 
 #include "torlog.h"
 #include "util.h"
@@ -3556,3 +3562,23 @@ get_total_system_memory(size_t *mem_out)
   return 0;
 }
 
+#ifdef TOR_UNIT_TESTS
+/** Delay for <b>msec</b> milliseconds.  Only used in tests. */
+void
+tor_sleep_msec(int msec)
+{
+#ifdef _WIN32
+  Sleep(msec);
+#elif defined(HAVE_USLEEP)
+  sleep(msec / 1000);
+  /* Some usleep()s hate sleeping more than 1 sec */
+  usleep((msec % 1000) * 1000);
+#elif defined(HAVE_SYS_SELECT_H)
+  struct timeval tv = { msec / 1000, (msec % 1000) * 1000};
+  select(0, NULL, NULL, NULL, &tv);
+#else
+  sleep(CEIL_DIV(msec, 1000));
+#endif
+}
+#endif
+

src/common/compat.h

@@ -749,6 +749,10 @@ char *format_win32_error(DWORD err);
 
 #endif
 
+#ifdef TOR_UNIT_TESTS
+void tor_sleep_msec(int msec);
+#endif
+
 #ifdef COMPAT_PRIVATE
 #if !defined(HAVE_SOCKETPAIR) || defined(_WIN32) || defined(TOR_UNIT_TESTS)
 #define NEED_ERSATZ_SOCKETPAIR

src/common/include.am

@@ -64,9 +64,9 @@ LIBOR_A_SOURCES = \
   src/common/di_ops.c					\
   src/common/log.c					\
   src/common/memarea.c					\
-  src/common/procmon.c					\
   src/common/util.c					\
   src/common/util_codedigest.c				\
+  src/common/util_process.c				\
   src/common/sandbox.c					\
   src/ext/csiphash.c					\
   $(libor_extra_source)					\
@@ -80,7 +80,9 @@ LIBOR_CRYPTO_A_SOURCES = \
   src/common/tortls.c		\
   $(libcrypto_extra_source)
 
-LIBOR_EVENT_A_SOURCES = src/common/compat_libevent.c
+LIBOR_EVENT_A_SOURCES = \
+	src/common/compat_libevent.c \
+	src/common/procmon.c
 
 src_common_libor_a_SOURCES = $(LIBOR_A_SOURCES)
 src_common_libor_crypto_a_SOURCES = $(LIBOR_CRYPTO_A_SOURCES)
@@ -119,6 +121,7 @@ COMMONHEADERS = \
   src/common/torlog.h				\
   src/common/tortls.h				\
   src/common/util.h				\
+  src/common/util_process.h			\
   $(libor_mempool_header)
 
 noinst_HEADERS+= $(COMMONHEADERS)

src/common/procmon.c

@@ -162,6 +162,7 @@ tor_validate_process_specifier(const char *process_spec,
   return parse_process_specifier(process_spec, &ppspec, msg);
 }
 
+/* XXXX we should use periodic_timer_new() for this stuff */
 #ifdef HAVE_EVENT2_EVENT_H
 #define PERIODIC_TIMER_FLAGS EV_PERSIST
 #else

src/common/util.c

@@ -26,6 +26,7 @@
 #include "address.h"
 #include "sandbox.h"
 #include "backtrace.h"
+#include "util_process.h"
 
 #ifdef _WIN32
 #include <io.h>
@@ -3629,13 +3630,7 @@ tor_terminate_process(process_handle_t *process_handle)
 {
 #ifdef _WIN32
   if (tor_get_exit_code(process_handle, 0, NULL) == PROCESS_EXIT_RUNNING) {
-    HANDLE handle;
-    /* If the signal is outside of what GenerateConsoleCtrlEvent can use,
-       attempt to open and terminate the process. */
-    handle = OpenProcess(PROCESS_ALL_ACCESS, FALSE,
-                         process_handle->pid.dwProcessId);
-    if (!handle)
-      return -1;
+    HANDLE handle = process_handle->pid.hProcess;
 
     if (!TerminateProcess(handle, 0))
       return -1;
@@ -3643,7 +3638,10 @@ tor_terminate_process(process_handle_t *process_handle)
       return 0;
   }
 #else /* Unix */
-  return kill(process_handle->pid, SIGTERM);
+  if (process_handle->waitpid_cb) {
+    /* We haven't got a waitpid yet, so we can just kill off the process. */
+    return kill(process_handle->pid, SIGTERM);
+  }
 #endif
 
   return -1;
@@ -3692,6 +3690,23 @@ process_handle_new(void)
   return out;
 }
 
+#ifndef _WIN32
+/** Invoked when a process that we've launched via tor_spawn_background() has
+ * been found to have terminated.
+ */
+static void
+process_handle_waitpid_cb(int status, void *arg)
+{
+  process_handle_t *process_handle = arg;
+
+  process_handle->waitpid_exit_status = status;
+  clear_waitpid_callback(process_handle->waitpid_cb);
+  if (process_handle->status == PROCESS_STATUS_RUNNING)
+    process_handle->status = PROCESS_STATUS_NOTRUNNING;
+  process_handle->waitpid_cb = 0;
+}
+#endif
+
 /**
  * @name child-process states
  *
@@ -4008,6 +4023,10 @@ tor_spawn_background(const char *const filename, const char **argv,
             strerror(errno));
   }
 
+  process_handle->waitpid_cb = set_waitpid_callback(pid,
+                                                    process_handle_waitpid_cb,
+                                                    process_handle);
+
   process_handle->stderr_pipe = stderr_pipe[0];
   retval = close(stderr_pipe[1]);
 
@@ -4072,6 +4091,8 @@ tor_process_handle_destroy,(process_handle_t *process_handle,
 
   if (process_handle->stderr_handle)
     fclose(process_handle->stderr_handle);
+
+  clear_waitpid_callback(process_handle->waitpid_cb);
 #endif
 
   memset(process_handle, 0x0f, sizeof(process_handle_t));
@@ -4089,7 +4110,7 @@ tor_process_handle_destroy,(process_handle_t *process_handle,
  * probably not work in Tor, because waitpid() is called in main.c to reap any
  * terminated child processes.*/
 int
-tor_get_exit_code(const process_handle_t *process_handle,
+tor_get_exit_code(process_handle_t *process_handle,
                   int block, int *exit_code)
 {
 #ifdef _WIN32
@@ -4129,7 +4150,20 @@ tor_get_exit_code(const process_handle_t *process_handle,
   int stat_loc;
   int retval;
 
-  retval = waitpid(process_handle->pid, &stat_loc, block?0:WNOHANG);
+  if (process_handle->waitpid_cb) {
+    /* We haven't processed a SIGCHLD yet. */
+    retval = waitpid(process_handle->pid, &stat_loc, block?0:WNOHANG);
+    if (retval == process_handle->pid) {
+      clear_waitpid_callback(process_handle->waitpid_cb);
+      process_handle->waitpid_cb = NULL;
+      process_handle->waitpid_exit_status = stat_loc;
+    }
+  } else {
+    /* We already got a SIGCHLD for this process, and handled it. */
+    retval = process_handle->pid;
+    stat_loc = process_handle->waitpid_exit_status;
+  }
+
   if (!block && 0 == retval) {
     /* Process has not exited */
     return PROCESS_EXIT_RUNNING;

src/common/util.h

@@ -446,6 +446,7 @@ void set_environment_variable_in_smartlist(struct smartlist_t *env_vars,
 #define PROCESS_STATUS_ERROR -1
 
 #ifdef UTIL_PRIVATE
+struct waitpid_callback_t;
 /** Structure to represent the state of a process with which Tor is
  * communicating. The contents of this structure are private to util.c */
 struct process_handle_t {
@@ -461,6 +462,12 @@ struct process_handle_t {
   FILE *stdout_handle;
   FILE *stderr_handle;
   pid_t pid;
+  /** If the process has not given us a SIGCHLD yet, this has the
+   * waitpid_callback_t that gets invoked once it has. Otherwise this
+   * contains NULL. */
+  struct waitpid_callback_t *waitpid_cb;
+  /** The exit status reported by waitpid. */
+  int waitpid_exit_status;
 #endif // _WIN32
 };
 #endif
@@ -469,7 +476,7 @@ struct process_handle_t {
 #define PROCESS_EXIT_RUNNING 1
 #define PROCESS_EXIT_EXITED 0
 #define PROCESS_EXIT_ERROR -1
-int tor_get_exit_code(const process_handle_t *process_handle,
+int tor_get_exit_code(process_handle_t *process_handle,
                       int block, int *exit_code);
 int tor_split_lines(struct smartlist_t *sl, char *buf, int len);
 #ifdef _WIN32

src/common/util_process.c

@@ -0,0 +1,157 @@
+/* Copyright (c) 2003-2004, Roger Dingledine
+ * Copyright (c) 2004-2006, Roger Dingledine, Nick Mathewson.
+ * Copyright (c) 2007-2013, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file util_process.c
+ * \brief utility functions for launching processes and checking their
+ *    status. These functions are kept separately from procmon so that they
+ *    won't require linking against libevent.
+ **/
+
+#include "orconfig.h"
+
+#ifdef HAVE_SYS_TYPES_H
+#include <sys/types.h>
+#endif
+#ifdef HAVE_SYS_WAIT_H
+#include <sys/wait.h>
+#endif
+
+#include "compat.h"
+#include "util.h"
+#include "torlog.h"
+#include "util_process.h"
+#include "ht.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.
+ */
+
+#ifndef _WIN32
+
+/** 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_GENERATE(process_map, waitpid_callback_t, node, process_map_entry_hash_,
+            process_map_entries_eq_, 0.6, malloc, realloc, 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
+

src/common/util_process.h

@@ -0,0 +1,25 @@
+/* Copyright (c) 2011-2013, The Tor Project, Inc. */
+/* See LICENSE for licensing information */
+
+/**
+ * \file util_process.h
+ * \brief Headers for util_process.c
+ **/
+
+#ifndef TOR_UTIL_PROCESS_H
+#define TOR_UTIL_PROCESS_H
+
+#ifndef _WIN32
+/** A callback structure waiting for us to get a SIGCHLD informing us that a
+ * PID has been closed. Created by set_waitpid_callback. Cancelled or cleaned-
+ * up from clear_waitpid_callback().  Do not access outside of the main thread;
+ * do not access from inside a signal handler. */
+typedef struct waitpid_callback_t waitpid_callback_t;
+
+waitpid_callback_t *set_waitpid_callback(pid_t pid,
+                                         void (*fn)(int, void *), void *arg);
+void clear_waitpid_callback(waitpid_callback_t *ent);
+void notify_pending_waitpid_callbacks(void);
+#endif
+
+#endif

src/or/main.c

@@ -54,6 +54,7 @@
 #include "routerparse.h"
 #include "statefile.h"
 #include "status.h"
+#include "util_process.h"
 #include "ext_orport.h"
 #ifdef USE_DMALLOC
 #include <dmalloc.h>
@@ -2109,8 +2110,7 @@ process_signal(uintptr_t sig)
       break;
 #ifdef SIGCHLD
     case SIGCHLD:
-      while (waitpid(-1,NULL,WNOHANG) > 0) ; /* keep reaping until no more
-                                                zombies */
+      notify_pending_waitpid_callbacks();
       break;
 #endif
     case SIGNEWNYM: {

src/or/or.h

@@ -42,9 +42,6 @@
 #include <sys/param.h> /* FreeBSD needs this to know what version it is */
 #endif
 #include "torint.h"
-#ifdef HAVE_SYS_WAIT_H
-#include <sys/wait.h>
-#endif
 #ifdef HAVE_SYS_FCNTL_H
 #include <sys/fcntl.h>
 #endif

src/test/test-child.c

@@ -9,6 +9,13 @@
 #else
 #include <unistd.h>
 #endif
+#include <string.h>
+
+#ifdef _WIN32
+#define SLEEP(sec) Sleep((sec)*1000)
+#else
+#define SLEEP(sec) sleep(sec)
+#endif
 
 /** Trivial test program which prints out its command line arguments so we can
  * check if tor_spawn_background() works */
@@ -16,27 +23,38 @@ int
 main(int argc, char **argv)
 {
   int i;
+  int delay = 1;
+  int fast = 0;
+
+  if (argc > 1)  {
+    if (!strcmp(argv[1], "--hang")) {
+      delay = 60;
+    } else if (!strcmp(argv[1], "--fast")) {
+      fast = 1;
+      delay = 0;
+    }
+  }
 
   fprintf(stdout, "OUT\n");
   fprintf(stderr, "ERR\n");
   for (i = 1; i < argc; i++)
     fprintf(stdout, "%s\n", argv[i]);
-  fprintf(stdout, "SLEEPING\n");
+  if (!fast)
+    fprintf(stdout, "SLEEPING\n");
   /* We need to flush stdout so that test_util_spawn_background_partial_read()
      succeed. Otherwise ReadFile() will get the entire output in one */
   // XXX: Can we make stdio flush on newline?
   fflush(stdout);
-#ifdef _WIN32
-  Sleep(1000);
-#else
-  sleep(1);
-#endif
+  if (!fast)
+    SLEEP(1);
   fprintf(stdout, "DONE\n");
-#ifdef _WIN32
-  Sleep(1000);
-#else
-  sleep(1);
-#endif
+  fflush(stdout);
+  if (fast)
+    return 0;
+
+  while (--delay) {
+    SLEEP(1);
+  }
 
   return 0;
 }

src/test/test_util.c

@@ -16,6 +16,7 @@
 #include "mempool.h"
 #endif /* ENABLE_MEMPOOLS */
 #include "memarea.h"
+#include "util_process.h"
 
 #ifdef _WIN32
 #include <tchar.h>
@@ -2538,6 +2539,19 @@ test_util_fgets_eagain(void *ptr)
 }
 #endif
 
+#ifndef BUILDDIR
+#define BUILDDIR "."
+#endif
+
+#ifdef _WIN32
+#define notify_pending_waitpid_callbacks() STMT_NIL
+#define TEST_CHILD "test-child.exe"
+#define EOL "\r\n"
+#else
+#define TEST_CHILD (BUILDDIR "/src/test/test-child")
+#define EOL "\n"
+#endif
+
 /** Helper function for testing tor_spawn_background */
 static void
 run_util_spawn_background(const char *argv[], const char *expected_out,
@@ -2557,19 +2571,28 @@ run_util_spawn_background(const char *argv[], const char *expected_out,
   status = tor_spawn_background(argv[0], argv, NULL, &process_handle);
 #endif
 
+  notify_pending_waitpid_callbacks();
+
   test_eq(expected_status, status);
-  if (status == PROCESS_STATUS_ERROR)
+  if (status == PROCESS_STATUS_ERROR) {
+    tt_ptr_op(process_handle, ==, NULL);
     return;
+  }
 
   test_assert(process_handle != NULL);
   test_eq(expected_status, process_handle->status);
 
+#ifndef _WIN32
+  notify_pending_waitpid_callbacks();
+  tt_ptr_op(process_handle->waitpid_cb, !=, NULL);
+#endif
+
 #ifdef _WIN32
   test_assert(process_handle->stdout_pipe != INVALID_HANDLE_VALUE);
   test_assert(process_handle->stderr_pipe != INVALID_HANDLE_VALUE);
 #else
-  test_assert(process_handle->stdout_pipe > 0);
-  test_assert(process_handle->stderr_pipe > 0);
+  test_assert(process_handle->stdout_pipe >= 0);
+  test_assert(process_handle->stderr_pipe >= 0);
 #endif
 
   /* Check stdout */
@@ -2580,12 +2603,19 @@ run_util_spawn_background(const char *argv[], const char *expected_out,
   test_eq(strlen(expected_out), pos);
   test_streq(expected_out, stdout_buf);
 
+  notify_pending_waitpid_callbacks();
+
   /* Check it terminated correctly */
   retval = tor_get_exit_code(process_handle, 1, &exit_code);
   test_eq(PROCESS_EXIT_EXITED, retval);
   test_eq(expected_exit, exit_code);
   // TODO: Make test-child exit with something other than 0
 
+#ifndef _WIN32
+  notify_pending_waitpid_callbacks();
+  tt_ptr_op(process_handle->waitpid_cb, ==, NULL);
+#endif
+
   /* Check stderr */
   pos = tor_read_all_from_process_stderr(process_handle, stderr_buf,
                                          sizeof(stderr_buf) - 1);
@@ -2594,6 +2624,8 @@ run_util_spawn_background(const char *argv[], const char *expected_out,
   test_streq(expected_err, stderr_buf);
   test_eq(strlen(expected_err), pos);
 
+  notify_pending_waitpid_callbacks();
+
  done:
   if (process_handle)
     tor_process_handle_destroy(process_handle, 1);
@@ -2603,29 +2635,20 @@ run_util_spawn_background(const char *argv[], const char *expected_out,
 static void
 test_util_spawn_background_ok(void *ptr)
 {
-#ifdef _WIN32
-  const char *argv[] = {"test-child.exe", "--test", NULL};
-  const char *expected_out = "OUT\r\n--test\r\nSLEEPING\r\nDONE\r\n";
-  const char *expected_err = "ERR\r\n";
-#else
-  const char *argv[] = {BUILDDIR "/src/test/test-child", "--test", NULL};
-  const char *expected_out = "OUT\n--test\nSLEEPING\nDONE\n";
-  const char *expected_err = "ERR\n";
-#endif
+  const char *argv[] = {TEST_CHILD, "--test", NULL};
+  const char *expected_out = "OUT"EOL "--test"EOL "SLEEPING"EOL "DONE" EOL;
+  const char *expected_err = "ERR"EOL;
 
   (void)ptr;
 
   run_util_spawn_background(argv, expected_out, expected_err, 0,
-                            PROCESS_STATUS_RUNNING);
+      PROCESS_STATUS_RUNNING);
 }
 
 /** Check that failing to find the executable works as expected */
 static void
 test_util_spawn_background_fail(void *ptr)
 {
-#ifndef BUILDDIR
-#define BUILDDIR "."
-#endif
   const char *argv[] = {BUILDDIR "/src/test/no-such-file", "--test", NULL};
   const char *expected_err = "";
   char expected_out[1024];
@@ -2646,13 +2669,13 @@ test_util_spawn_background_fail(void *ptr)
     "ERR: Failed to spawn background process - code %s\n", code);
 
   run_util_spawn_background(argv, expected_out, expected_err, 255,
-                            expected_status);
+      expected_status);
 }
 
 /** Test that reading from a handle returns a partial read rather than
  * blocking */
 static void
-test_util_spawn_background_partial_read(void *ptr)
+test_util_spawn_background_partial_read_impl(int exit_early)
 {
   const int expected_exit = 0;
   const int expected_status = PROCESS_STATUS_RUNNING;
@@ -2662,22 +2685,22 @@ test_util_spawn_background_partial_read(void *ptr)
   process_handle_t *process_handle=NULL;
   int status;
   char stdout_buf[100], stderr_buf[100];
-#ifdef _WIN32
-  const char *argv[] = {"test-child.exe", "--test", NULL};
-  const char *expected_out[] = { "OUT\r\n--test\r\nSLEEPING\r\n",
-                                 "DONE\r\n",
-                                 NULL };
-  const char *expected_err = "ERR\r\n";
-#else
-  const char *argv[] = {BUILDDIR "/src/test/test-child", "--test", NULL};
-  const char *expected_out[] = { "OUT\n--test\nSLEEPING\n",
-                                 "DONE\n",
+
+  const char *argv[] = {TEST_CHILD, "--test", NULL};
+  const char *expected_out[] = { "OUT" EOL "--test" EOL "SLEEPING" EOL,
+                                 "DONE" EOL,
                                  NULL };
-  const char *expected_err = "ERR\n";
+  const char *expected_err = "ERR" EOL;
+
+#ifndef _WIN32
   int eof = 0;
 #endif
   int expected_out_ctr;
-  (void)ptr;
+
+  if (exit_early) {
+    argv[1] = "--hang";
+    expected_out[0] = "OUT"EOL "--hang"EOL "SLEEPING" EOL;
+  }
 
   /* Start the program */
 #ifdef _WIN32
@@ -2713,6 +2736,12 @@ test_util_spawn_background_partial_read(void *ptr)
     expected_out_ctr++;
   }
 
+  if (exit_early) {
+    tor_process_handle_destroy(process_handle, 1);
+    process_handle = NULL;
+    goto done;
+  }
+
   /* The process should have exited without writing more */
 #ifdef _WIN32
   pos = tor_read_all_handle(process_handle->stdout_pipe, stdout_buf,
@@ -2750,6 +2779,75 @@ test_util_spawn_background_partial_read(void *ptr)
   tor_process_handle_destroy(process_handle, 1);
 }
 
+static void
+test_util_spawn_background_partial_read(void *arg)
+{
+  (void)arg;
+  test_util_spawn_background_partial_read_impl(0);
+}
+
+static void
+test_util_spawn_background_exit_early(void *arg)
+{
+  (void)arg;
+  test_util_spawn_background_partial_read_impl(1);
+}
+
+static void
+test_util_spawn_background_waitpid_notify(void *arg)
+{
+  int retval, exit_code;
+  process_handle_t *process_handle=NULL;
+  int status;
+  int ms_timer;
+
+  const char *argv[] = {TEST_CHILD, "--fast", NULL};
+
+  (void) arg;
+
+#ifdef _WIN32
+  status = tor_spawn_background(NULL, argv, NULL, &process_handle);
+#else
+  status = tor_spawn_background(argv[0], argv, NULL, &process_handle);
+#endif
+
+  tt_int_op(status, ==, PROCESS_STATUS_RUNNING);
+  tt_ptr_op(process_handle, !=, NULL);
+
+  /* We're not going to look at the stdout/stderr output this time. Instead,
+   * we're testing whether notify_pending_waitpid_calbacks() can report the
+   * process exit (on unix) and/or whether tor_get_exit_code() can notice it
+   * (on windows) */
+
+#ifndef _WIN32
+  ms_timer = 30*1000;
+  tt_ptr_op(process_handle->waitpid_cb, !=, NULL);
+  while (process_handle->waitpid_cb && ms_timer > 0) {
+    tor_sleep_msec(100);
+    ms_timer -= 100;
+    notify_pending_waitpid_callbacks();
+  }
+  tt_int_op(ms_timer, >, 0);
+  tt_ptr_op(process_handle->waitpid_cb, ==, NULL);
+#endif
+
+  ms_timer = 30*1000;
+  while (((retval = tor_get_exit_code(process_handle, 0, &exit_code))
+                == PROCESS_EXIT_RUNNING) && ms_timer > 0) {
+    tor_sleep_msec(100);
+    ms_timer -= 100;
+  }
+  tt_int_op(ms_timer, >, 0);
+
+  tt_int_op(retval, ==, PROCESS_EXIT_EXITED);
+
+ done:
+  tor_process_handle_destroy(process_handle, 1);
+}
+
+#undef TEST_CHILD
+#undef EOL
+
 /**
  * Test for format_hex_number_sigsafe()
  */
@@ -3695,6 +3793,8 @@ struct testcase_t util_tests[] = {
   UTIL_TEST(spawn_background_ok, 0),
   UTIL_TEST(spawn_background_fail, 0),
   UTIL_TEST(spawn_background_partial_read, 0),
+  UTIL_TEST(spawn_background_exit_early, 0),
+  UTIL_TEST(spawn_background_waitpid_notify, 0),
   UTIL_TEST(format_hex_number, 0),
   UTIL_TEST(format_dec_number, 0),
   UTIL_TEST(join_win_cmdline, 0),