Fix #10017

Summary:
In the threaded RTS, a signal is delivered from the RTS to Haskell
user code by writing to file that one of the IO managers watches (via
an instance of GHC.Event.Control.Control). When the IO manager
receives the signal, it calls GHC.Conc.Signal.runHandlers to invoke
Haskell signal handler. In the move from a single IO manager to one IO
manager per capability, the behavior was (wrongly) extended so that a
signal is delivered to every event manager (see #9423), each of which
invoke Haskell signal handlers, leading to multiple invocations of
Haskell signal handlers for a single signal. This change fixes this
problem by having the RTS (in generic_handler()) notify only the
Control instance used by the TimerManager, rather than all the
per-capability IO managers.

Reviewers: austin, hvr, simonmar, Mikolaj

Reviewed By: simonmar, Mikolaj

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D641

5 files changed, 15 insertions, 14 deletions

diff --git a/libraries/base/GHC/Event/Manager.hs b/libraries/base/GHC/Event/Manager.hs
index eeda1c833d..11b01ade36 100644
--- a/libraries/base/GHC/Event/Manager.hs
+++ b/libraries/base/GHC/Event/Manager.hs
@@ -72,7 +72,6 @@ import Data.Maybe (maybe)
 import Data.OldList (partition)
 import GHC.Arr (Array, (!), listArray)
 import GHC.Base
-import GHC.Conc.Signal (runHandlers)
 import GHC.Conc.Sync (yield)
 import GHC.List (filter, replicate)
 import GHC.Num (Num(..))
@@ -163,7 +162,7 @@ handleControlEvent mgr fd _evt = do
   case msg of
     CMsgWakeup      -> return ()
     CMsgDie         -> writeIORef (emState mgr) Finished
-    CMsgSignal fp s -> runHandlers fp s
+    _               -> return ()
 
 newDefaultBackend :: IO Backend
 #if defined(HAVE_KQUEUE)
diff --git a/rts/posix/Signals.c b/rts/posix/Signals.c
index 44bd0b6d9c..5fbb917cf8 100644
--- a/rts/posix/Signals.c
+++ b/rts/posix/Signals.c
@@ -251,18 +251,6 @@ generic_handler(int sig USED_IF_THREADS,
         }
     }
 
-    nat i;
-    int fd;
-    for (i=0; i < n_capabilities; i++) {
-        fd = capabilities[i]->io_manager_control_wr_fd;
-        if (0 <= fd) {
-            r = write(fd, buf, sizeof(siginfo_t)+1);
-            if (r == -1 && errno == EAGAIN) {
-                errorBelch("lost signal due to full pipe: %d\n", sig);
-            }
-        }
-    }
-
     // If the IO manager hasn't told us what the FD of the write end
     // of its pipe is, there's not much we can do here, so just ignore
     // the signal..
diff --git a/testsuite/tests/rts/T10017.hs b/testsuite/tests/rts/T10017.hs
new file mode 100644
index 0000000000..ed34841abb
--- /dev/null
+++ b/testsuite/tests/rts/T10017.hs
@@ -0,0 +1,11 @@
+import Control.Concurrent
+import System.Posix.Signals
+
+main :: IO ()
+main = do
+    _ <- flip (installHandler sig) Nothing $ Catch $
+        putStrLn $ "Received my signal"
+    raiseSignal sig
+    threadDelay 100000
+  where
+    sig = sigUSR2
diff --git a/testsuite/tests/rts/T10017.stdout b/testsuite/tests/rts/T10017.stdout
new file mode 100644
index 0000000000..f138924616
--- /dev/null
+++ b/testsuite/tests/rts/T10017.stdout
@@ -0,0 +1 @@
+Received my signal
diff --git a/testsuite/tests/rts/all.T b/testsuite/tests/rts/all.T
index 89f1da81d5..88c354f2f5 100644
--- a/testsuite/tests/rts/all.T
+++ b/testsuite/tests/rts/all.T
@@ -238,6 +238,8 @@ test('T9045', [ omit_ways(['ghci']), extra_run_opts('10000 +RTS -A8k -RTS') ], c
 # with the non-threaded one.
 test('T9078', [ omit_ways(threaded_ways) ], compile_and_run, ['-with-rtsopts="-DS" -debug'])
 
+test('T10017', [ only_ways(threaded_ways), extra_run_opts('+RTS -N2 -RTS') ], compile_and_run, [''])
+
 test('rdynamic', [ unless(opsys('linux') or opsys('mingw32'), skip)
                  # this needs runtime infrastructure to do in ghci:
                  #  '-rdynamic' ghc, load modules only via dlopen(RTLD_BLOBAL) and more.