r15251@tombo: nickm | 2008-04-22 11:59:46 -0400

 On platforms using pthreads, allow a thread to acquire a lock it already holds.  This is crucial for logging: otherwise any log message thrown from inside the logging process (especially from control.c) will deadlock.  Win32 CriticalSections are already recursive.  Bug spotted by nwf.  Bugfix on 0.2.0.16-alpha.  Backport candidate. I hope this is portable.


svn:r14406

ChangeLog

@@ -24,6 +24,9 @@ Changes in version 0.2.1.1-alpha - 2008-??-??
       most smartlists hold around 8-12 elements tops.
     - Avoid allocating extra space when computing consensuses on
       64-bit platforms.  Bug spotted by aakova.
+    - Use recursive pthread mutexes in order to avoid deadlock when
+      logging debug-level messages to a controller.  Bug spotted by
+      nwf, bugfix on 0.2.0.16-alpha.
 
   o Minor features:
     - Allow separate log levels to be configured for different logging

src/common/compat.c

@@ -1735,13 +1735,14 @@ tor_get_thread_id(void)
 struct tor_mutex_t {
   pthread_mutex_t mutex;
 };
+static pthread_mutexattr_t attr_reentrant;
 /** Allocate and return new lock. */
 tor_mutex_t *
 tor_mutex_new(void)
 {
   int err;
   tor_mutex_t *mutex = tor_malloc_zero(sizeof(tor_mutex_t));
-  err = pthread_mutex_init(&mutex->mutex, NULL);
+  err = pthread_mutex_init(&mutex->mutex, &attr_reentrant);
   if (PREDICT_UNLIKELY(err)) {
     log_err(LD_GENERAL, "Error %d creating a mutex.", err);
     tor_fragile_assert();
@@ -1857,6 +1858,10 @@ tor_cond_signal_all(tor_cond_t *cond)
 void
 tor_threads_init(void)
 {
+#ifdef USE_PTHREADS
+  pthread_mutexattr_init(&attr_reentrant);
+  pthread_mutexattr_settype(&attr_reentrant, PTHREAD_MUTEX_RECURSIVE);
+#endif
 }
 #elif defined(USE_WIN32_THREADS)
 #if 0