ipc: fix IO::FDPass use with a worker limit of 1

IO::FDPass is our last choice for implementing the workqueue
because its lack of atomicity makes it impossible to guarantee
all requests of a single group hit a single worker out of many.

So the only way to use IO::FDPass for workqueues it to only have
a single worker.  A single worker still buys us a small amount
of parallelism because of the parent process.

1 files changed, 11 insertions, 7 deletions

diff --git a/t/ipc.t b/t/ipc.t
index d2b6ad4f..fd290809 100644
--- a/t/ipc.t
+++ b/t/ipc.t
@@ -171,13 +171,17 @@ is($warn[2], $warn[1], 'worker did not die');
 $SIG{__WARN__} = 'DEFAULT';
 is($ipc->wq_workers_start('wq', 1), $$, 'workers started again');
 is($ipc->wq_workers, 1, '1 worker started');
-$ipc->wq_worker_incr;
-is($ipc->wq_workers, 2, 'worker count bumped');
-$ipc->wq_worker_decr;
-$ipc->wq_worker_decr_wait(10);
-is($ipc->wq_workers, 1, 'worker count lowered');
-is($ipc->wq_workers(2), 2, 'worker count set');
-is($ipc->wq_workers, 2, 'worker count stayed set');
+SKIP: {
+        $ipc->WQ_MAX_WORKERS > 1 or
+                skip 'Inline::C or Socket::MsgHdr not available', 4;
+        $ipc->wq_worker_incr;
+        is($ipc->wq_workers, 2, 'worker count bumped');
+        $ipc->wq_worker_decr;
+        $ipc->wq_worker_decr_wait(10);
+        is($ipc->wq_workers, 1, 'worker count lowered');
+        is($ipc->wq_workers(2), 2, 'worker count set');
+        is($ipc->wq_workers, 2, 'worker count stayed set');
+}
 $ipc->wq_close;
 is($ipc->wq_workers, undef, 'workers undef after close');