ovs-thread: Add support for various thread-related assertions.

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Ethan Jackson <ethan@nicira.com>

lib/command-line.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008, 2009, 2010, 2011 Nicira, Inc.
+ * Copyright (c) 2008, 2009, 2010, 2011, 2013 Nicira, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -19,6 +19,7 @@
 #include <getopt.h>
 #include <limits.h>
 #include <stdlib.h>
+#include "ovs-thread.h"
 #include "util.h"
 #include "vlog.h"
 
@@ -110,6 +111,7 @@ proctitle_init(int argc, char **argv)
 {
     int i;
 
+    assert_single_threaded();
     if (!argc || !argv[0]) {
         /* This situation should never occur, but... */
         return;

lib/daemon.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2008, 2009, 2010, 2011, 2012 Nicira, Inc.
+ * Copyright (c) 2008, 2009, 2010, 2011, 2012, 2013 Nicira, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -29,6 +29,7 @@
 #include "fatal-signal.h"
 #include "dirs.h"
 #include "lockfile.h"
+#include "ovs-thread.h"
 #include "process.h"
 #include "socket-util.h"
 #include "timeval.h"
@@ -88,6 +89,7 @@ make_pidfile_name(const char *name)
 void
 set_pidfile(const char *name)
 {
+    assert_single_threaded();
     free(pidfile);
     pidfile = make_pidfile_name(name);
 }
@@ -280,9 +282,7 @@ daemonize(void)
 pid_t
 fork_and_clean_up(void)
 {
-    pid_t pid;
+    pid_t pid = xfork();
-
-    pid = fork();
     if (pid > 0) {
         /* Running in parent process. */
         fatal_signal_fork();
@@ -290,10 +290,7 @@ fork_and_clean_up(void)
         /* Running in child process. */
         time_postfork();
         lockfile_postfork();
-    } else {
-        VLOG_FATAL("fork failed (%s)", strerror(errno));
     }
-
     return pid;
 }
 
@@ -504,6 +501,7 @@ close_standard_fds(void)
 void
 daemonize_start(void)
 {
+    assert_single_threaded();
     daemonize_fd = -1;
 
     if (detach) {

lib/ofp-version-opt.c

@@ -1,6 +1,7 @@
 #include <config.h>
 #include "ofp-util.h"
 #include "ofp-version-opt.h"
+#include "ovs-thread.h"
 #include "vlog.h"
 #include "dynamic-string.h"
 
@@ -17,12 +18,14 @@ get_allowed_ofp_versions(void)
 void
 set_allowed_ofp_versions(const char *string)
 {
+    assert_single_threaded();
     allowed_versions = ofputil_versions_from_string(string);
 }
 
 void
 mask_allowed_ofp_versions(uint32_t bitmap)
 {
+    assert_single_threaded();
     allowed_versions &= bitmap;
 }
 

lib/ovs-thread.c

@@ -17,7 +17,12 @@
 #include <config.h>
 #include "ovs-thread.h"
 #include <errno.h>
+#include <poll.h>
+#include <stdlib.h>
+#include <unistd.h>
 #include "compiler.h"
+#include "poll-loop.h"
+#include "socket-util.h"
 #include "util.h"
 
 #ifdef __CHECKER__
@@ -26,6 +31,18 @@
  * cut-and-paste.  Since "sparse" is just a checker, not a compiler, it
  * doesn't matter that we don't define them. */
 #else
+#include "vlog.h"
+
+VLOG_DEFINE_THIS_MODULE(ovs_thread);
+
+/* If there is a reason that we cannot fork anymore (unless the fork will be
+ * immediately followed by an exec), then this points to a string that
+ * explains why. */
+static const char *must_not_fork;
+
+/* True if we created any threads beyond the main initial thread. */
+static bool multithreaded;
+
 #define XPTHREAD_FUNC1(FUNCTION, PARAM1)                \
     void                                                \
     x##FUNCTION(PARAM1 arg1)                            \
@@ -83,6 +100,9 @@ xpthread_create(pthread_t *threadp, pthread_attr_t *attr,
     pthread_t thread;
     int error;
 
+    forbid_forking("multiple threads exist");
+    multithreaded = true;
+
     error = pthread_create(threadp ? threadp : &thread, attr, start, arg);
     if (error) {
         ovs_abort(error, "pthread_create failed");
@@ -106,4 +126,52 @@ ovsthread_once_done(struct ovsthread_once *once)
     atomic_store(&once->done, true);
     xpthread_mutex_unlock(&once->mutex);
 }
+
+/* Asserts that the process has not yet created any threads (beyond the initial
+ * thread).  */
+void
+(assert_single_threaded)(const char *where)
+{
+    if (multithreaded) {
+        VLOG_FATAL("%s: attempted operation not allowed when multithreaded",
+                   where);
+    }
+}
+
+/* Forks the current process (checking that this is allowed).  Aborts with
+ * VLOG_FATAL if fork() returns an error, and otherwise returns the value
+ * returned by fork().  */
+pid_t
+(xfork)(const char *where)
+{
+    pid_t pid;
+
+    if (must_not_fork) {
+        VLOG_FATAL("%s: attempted to fork but forking not allowed (%s)",
+                   where, must_not_fork);
+    }
+
+    pid = fork();
+    if (pid < 0) {
+        VLOG_FATAL("fork failed (%s)", strerror(errno));
+    }
+    return pid;
+}
+
+/* Notes that the process must not call fork() from now on, for the specified
+ * 'reason'.  (The process may still fork() if it execs itself immediately
+ * afterward.) */
+void
+forbid_forking(const char *reason)
+{
+    ovs_assert(reason != NULL);
+    must_not_fork = reason;
+}
+
+/* Returns true if the process is allowed to fork, false otherwise. */
+bool
+may_fork(void)
+{
+    return !must_not_fork;
+}
 #endif

lib/ovs-thread.h

@@ -18,6 +18,8 @@
 #define OVS_THREAD_H 1
 
 #include <pthread.h>
+#include <stddef.h>
+#include <sys/types.h>
 #include "ovs-atomic.h"
 #include "util.h"
 
@@ -365,5 +367,14 @@ ovsthread_once_start(struct ovsthread_once *once)
 #define ovsthread_once_start(ONCE) \
     ((ONCE)->done ? false : ({ OVS_ACQUIRE(ONCE); true; }))
 #endif
+
+void assert_single_threaded(const char *where);
+#define assert_single_threaded() assert_single_threaded(SOURCE_LOCATOR)
+
+pid_t xfork(const char *where);
+#define xfork() xfork(SOURCE_LOCATOR)
+
+void forbid_forking(const char *reason);
+bool may_fork(void);
 
 #endif /* ovs-thread.h */

lib/process.c

@@ -28,6 +28,7 @@
 #include "dynamic-string.h"
 #include "fatal-signal.h"
 #include "list.h"
+#include "ovs-thread.h"
 #include "poll-loop.h"
 #include "signals.h"
 #include "socket-util.h"
@@ -71,6 +72,7 @@ process_init(void)
     static bool inited;
     struct sigaction sa;
 
+    assert_single_threaded();
     if (inited) {
         return;
     }
@@ -180,6 +182,8 @@ process_start(char **argv, struct process **pp)
     pid_t pid;
     int error;
 
+    assert_single_threaded();
+
     *pp = NULL;
     COVERAGE_INC(process_start);
     error = process_prestart(argv);

lib/timeval.c

@@ -30,6 +30,7 @@
 #include "fatal-signal.h"
 #include "hash.h"
 #include "hmap.h"
+#include "ovs-thread.h"
 #include "signals.h"
 #include "unixctl.h"
 #include "util.h"
@@ -297,6 +298,7 @@ time_alarm(unsigned int secs)
     long long int now;
     long long int msecs;
 
+    assert_single_threaded();
     time_init();
     time_refresh();
 

lib/util.c

@@ -27,6 +27,7 @@
 #include <unistd.h>
 #include "byte-order.h"
 #include "coverage.h"
+#include "ovs-thread.h"
 #include "vlog.h"
 
 VLOG_DEFINE_THIS_MODULE(util);
@@ -339,6 +340,9 @@ set_program_name__(const char *argv0, const char *version, const char *date,
                    const char *time)
 {
     const char *slash = strrchr(argv0, '/');
+
+    assert_single_threaded();
+
     program_name = slash ? slash + 1 : argv0;
 
     free(program_version);