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Date: Wed, 21 Nov 2018 09:55:20 +0000
From: Eric Wong <normalperson@yhbt.net>
To: spew@80x24.org
Subject: switch disable on mutex
Message-ID: <20181121095520.v4ddgpn6lufbvuvt@whir>
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diff --git a/iom_pingable_common.h b/iom_pingable_common.h
index 07841b44ca3..2e8c880f68d 100644
--- a/iom_pingable_common.h
+++ b/iom_pingable_common.h
@@ -214,7 +214,7 @@ rb_iom_fd(const rb_thread_t *th)
 static int
 rb_iom_schedule_p(const rb_thread_t *th)
 {
-    return rb_tl_sched_p(th->ec);
+    return rb_tl_sched_p(th->ec) && rb_tl_switchable(th->ec);
 }
 
 static void
diff --git a/iom_select.h b/iom_select.h
index 841104fb017..db51ac7a75f 100644
--- a/iom_select.h
+++ b/iom_select.h
@@ -541,13 +541,21 @@ rb_iom_schedule_p(const rb_thread_t *th)
 {
     rb_iom_t *iom = th->vm->iom;
 
-    if (rb_tl_sched_p(th->ec)) return 1;
+    if (!rb_tl_switchable(th->ec)) {
+        return 0;
+    }
+    if (rb_tl_sched_p(th->ec)) {
+        return 1;
+    }
 
+    /*
+     * select is different from the epoll/kqueue iom implementations
+     * since it's O(n) every call anyways, so we might as well run
+     * select() so that it covers as many FDs as possible
+     * FIXME: we sometimes miss wakeups if we use select for waiting
+     * on native threads unfortunately:
+     */
     if (iom && list_empty(&iom->c.blockers) && iom_events_pending(th->vm)) {
-        /*
-         * FIXME: we sometimes miss wakeups if we use select for waiting
-         * on native threads unfortunately:
-         */
         return 1;
     }
     return 0;
diff --git a/vm_core.h b/vm_core.h
index 9e10b321da2..2244afb5248 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -1846,6 +1846,9 @@ rb_tl_switchable(const rb_execution_context_t *ec)
     /* dangerous, don't allow switching inside trap handler: */
     if (ec->interrupt_mask & TRAP_INTERRUPT_MASK) return 0;
 
+    /* don't switch if a Mutex is held */
+    if (th->keeping_mutexes) return 0;
+
     /* auto-fibers can switch away to root fiber */
     if (rb_tl_sched_p(ec)) return 1;