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From 9e94fffba8ffbc9af4a6ceb75a78d2dab2da5682 Mon Sep 17 00:00:00 2001
From: Justus Winter <4winter@informatik.uni-hamburg.de>
Date: Mon, 15 Dec 2014 11:53:26 +0100
Subject: [PATCH hurd 1/2] libports: avoid acquiring global lock in message
dispatch
* libports/interrupt-operation.c (ports_S_interrupt_operation): Update
`cancel_threshold' using atomic operations.
* libports/manage-multithread.c (internal_demuxer): Avoid taking the lock.
* libports/ports.h (struct port_info): Mention that one needs atomic
operations to access `cancel_threshold'.
---
libports/interrupt-operation.c | 14 ++++++++++----
libports/manage-multithread.c | 8 +++++---
libports/ports.h | 2 +-
3 files changed, 16 insertions(+), 8 deletions(-)
diff --git a/libports/interrupt-operation.c b/libports/interrupt-operation.c
index 943bd4f..5d4b0b7 100644
--- a/libports/interrupt-operation.c
+++ b/libports/interrupt-operation.c
@@ -27,12 +27,18 @@ kern_return_t
ports_S_interrupt_operation (struct port_info *pi,
mach_port_seqno_t seqno)
{
+ mach_port_seqno_t old;
+
if (!pi)
return EOPNOTSUPP;
- pthread_mutex_lock (&_ports_lock);
- if (pi->cancel_threshold < seqno)
- pi->cancel_threshold = seqno;
- pthread_mutex_unlock (&_ports_lock);
+
+ retry:
+ old = __atomic_load_n (&pi->cancel_threshold, __ATOMIC_SEQ_CST);
+ if (old < seqno
+ && ! __atomic_compare_exchange_n (&pi->cancel_threshold, &old, seqno,
+ 0, __ATOMIC_SEQ_CST, __ATOMIC_SEQ_CST))
+ goto retry;
+
ports_interrupt_rpcs (pi);
return 0;
}
diff --git a/libports/manage-multithread.c b/libports/manage-multithread.c
index 2067cba..7d2e126 100644
--- a/libports/manage-multithread.c
+++ b/libports/manage-multithread.c
@@ -173,10 +173,12 @@ ports_manage_port_operations_multithread (struct port_bucket *bucket,
}
else
{
- pthread_mutex_lock (&_ports_lock);
- if (inp->msgh_seqno < pi->cancel_threshold)
+ mach_port_seqno_t cancel_threshold =
+ __atomic_load_n (&pi->cancel_threshold, __ATOMIC_SEQ_CST);
+
+ if (inp->msgh_seqno < cancel_threshold)
hurd_thread_cancel (link.thread);
- pthread_mutex_unlock (&_ports_lock);
+
status = demuxer (inp, outheadp);
ports_end_rpc (pi, &link);
}
diff --git a/libports/ports.h b/libports/ports.h
index a625b47..f02edb4 100644
--- a/libports/ports.h
+++ b/libports/ports.h
@@ -48,7 +48,7 @@ struct port_info
struct port_class *class;
refcounts_t refcounts;
mach_port_mscount_t mscount;
- mach_msg_seqno_t cancel_threshold;
+ mach_msg_seqno_t cancel_threshold; /* needs atomic operations */
int flags;
mach_port_t port_right;
struct rpc_info *current_rpcs;
--
2.1.3
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