Merge remote-tracking branch 'origin/version/5.5.2'

Author: grafikrobot

doc/src/history.adoc

@@ -3,9 +3,17 @@
 
 == Version 5.6.0
 
+== Version 5.5.2
+
+* Fix invalid use of system `ar` when cross-compiling with llvm on Linux instead
+  of defaulting to the matching cross-compiler `llvm-ar`.
+  -- _Uilian Ries_
 * Fix use of obsolete/deprecated `-single_module` option in darwin/mscOS
   tooling.
   -- _René Ferdinand Rivera Morell_
+* Fix startup, post-config, crashes when building B2 for install after
+  bootstrap.
+  -- _René Ferdinand Rivera Morell_
 
 == Version 5.5.1
 

src/engine/tasks.cpp

@@ -172,7 +172,12 @@ inline void group::implementation::call_queue(std::function<void()> f)
 			running -= 1;
 			signal_finished = pending.empty() && running == 0;
 		}
-		if (signal_finished) finished.signal();
+		if (signal_finished)
+		{
+			// Re-try the signal until it happens indicating that the waiting
+			// task is expecting it.
+			while (!finished.signal()) ;
+		}
 	};
 	{
 		scope_lock_t lock(mx);