Implement parallel error propagation, keep_going mode

Keep going is the default but there is now the -s|--serial-stop that makes
the driver run serially and stop at first error.

Also fix some lockups, other minor improvements/features.

1 files changed, 9 insertions, 3 deletions

diff --git a/build2/algorithm b/build2/algorithm
index 5ee6c64..33da884 100644
--- a/build2/algorithm
+++ b/build2/algorithm
@@ -149,9 +149,11 @@ namespace build2
 
   // Execute the action on target, assuming a rule has been matched and the
   // recipe for this action has been set. This is the synchrounous executor
-  // implementation (but may still return target_state::busy is the target
+  // implementation (but may still return target_state::busy if the target
   // is already being executed). Decrements the dependents count.
   //
+  // Note: does not translate target_state::failed to the failed exception.
+  //
   target_state
   execute (action, const target&);
 
@@ -159,6 +161,8 @@ namespace build2
   // if the asynchrounous execution has been started and target_state::busy if
   // the target has already been busy.
   //
+  // Note: does not translate target_state::failed to the failed exception.
+  //
   target_state
   execute_async (action, const target&,
                  size_t start_count, atomic_count& task_count);
@@ -174,8 +178,10 @@ namespace build2
   // A special version of the above that should be used for "direct" and "now"
   // execution, that is, side-stepping the normal target-prerequisite
   // relationship (so no dependents count is decremented) and execution order
-  // (so this function never returns the postponed target state). It will also
-  // wait for the completion if the target is busy.
+  // (so this function never returns the postponed target state).
+  //
+  // Note: waits for the completion if the target is busy and translates
+  // target_state::failed to the failed exception.
   //
   target_state
   execute_direct (action, const target&);