3 files changed, 24 insertions, 0 deletions
diff --git a/src/common/compat.c b/src/common/compat.c
index 35bb3a9ad3..d62b1ce1f4 100644
--- a/src/common/compat.c
+++ b/src/common/compat.c
@@ -2076,6 +2076,7 @@ tor_threads_init(void)
     pthread_mutexattr_init(&attr_reentrant);
     pthread_mutexattr_settype(&attr_reentrant, PTHREAD_MUTEX_RECURSIVE);
     threads_initialized = 1;
+    set_main_thread();
   }
 }
 #elif defined(USE_WIN32_THREADS)
@@ -2168,9 +2169,27 @@ tor_threads_init(void)
 #if 0
   cond_event_tls_index = TlsAlloc();
 #endif
+  set_main_thread();
 }
 #endif
 
+/** Identity of the "main" thread */
+static unsigned long main_thread_id = -1;
+
+/** Start considering the current thread to be the 'main thread'.  This has
+ * no effect on anything besides in_main_thread(). */
+void
+set_main_thread(void)
+{
+  main_thread_id = tor_get_thread_id();
+}
+/** Return true iff called from the main thread. */
+int
+in_main_thread(void)
+{
+  return main_thread_id == tor_get_thread_id();
+}
+
 /**
  * On Windows, WSAEWOULDBLOCK is not always correct: when you see it,
  * you need to ask the socket for its actual errno.  Also, you need to
diff --git a/src/common/compat.h b/src/common/compat.h
index edc38faf64..4d5a016cf2 100644
--- a/src/common/compat.h
+++ b/src/common/compat.h
@@ -522,6 +522,9 @@ void tor_threads_init(void);
 #define tor_threads_init() STMT_NIL
 #endif
 
+void set_main_thread(void);
+int in_main_thread(void);
+
 #ifdef TOR_IS_MULTITHREADED
 #if 0
 typedef struct tor_cond_t tor_cond_t;
diff --git a/src/common/util.c b/src/common/util.c
index a3338b1d18..7b9e5eb562 100644
--- a/src/common/util.c
+++ b/src/common/util.c
@@ -2480,6 +2480,8 @@ start_daemon(void)
     if (fork() != 0) {
       exit(0);
     }
+    set_main_thread(); /* We are now the main thread. */
+
     return;
   }
 }