[trafficserver] branch master updated: spawn_thread with atomic operation

[ok...@apache.org]

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oknet pushed a commit to branch master
in repository https://gitbox.apache.org/repos/asf/trafficserver.git

The following commit(s) were added to refs/heads/master by this push:
       new  05cc3df   spawn_thread with atomic operation
05cc3df is described below

commit 05cc3df86672cbb16f17e8909c8b471fac618d4a
Author: Oknet Xu <xu...@skyguard.com.cn>
AuthorDate: Wed May 24 21:20:38 2017 +0800

    spawn_thread with atomic operation
    
    The eventProcessor.spawn_thread() is used to create a DEDICATED EThread.
    The n_dthreads is total number of DEDICATED EThreads. When a new
    DEDICATED EThread created, it makes the `all_dthreads[n_dthreads]' point
    to the EThread object then do `n_dthreads++'
    
    It is not likes the spawn_event_threads() that only called from main()
    before any EThread runs. It is can be called from main() and/or any
    EThread.
    
    Therefore there is a race on accessing `all_dthreads[n_dthreads]' and
    `n_dthreads++'.
---
 iocore/eventsystem/I_EventProcessor.h    |  2 +-
 iocore/eventsystem/UnixEventProcessor.cc | 12 ++++++++----
 2 files changed, 9 insertions(+), 5 deletions(-)

diff --git a/iocore/eventsystem/I_EventProcessor.h b/iocore/eventsystem/I_EventProcessor.h
index 53923d5..5e1d112 100644
--- a/iocore/eventsystem/I_EventProcessor.h
+++ b/iocore/eventsystem/I_EventProcessor.h
@@ -307,7 +307,7 @@ public:
   EThread *assign_thread(EventType etype);
 
   EThread *all_dthreads[MAX_EVENT_THREADS];
-  int n_dthreads; // No. of dedicated threads
+  volatile int n_dthreads; // No. of dedicated threads
   volatile int thread_data_used;
 };
 
diff --git a/iocore/eventsystem/UnixEventProcessor.cc b/iocore/eventsystem/UnixEventProcessor.cc
index 853d347..2b06c84 100644
--- a/iocore/eventsystem/UnixEventProcessor.cc
+++ b/iocore/eventsystem/UnixEventProcessor.cc
@@ -266,13 +266,17 @@ Event *
 EventProcessor::spawn_thread(Continuation *cont, const char *thr_name, size_t stacksize)
 {
   ink_release_assert(n_dthreads < MAX_EVENT_THREADS);
+  int n = ink_atomic_increment((int *)&n_dthreads, 1);
+  ink_release_assert(n < MAX_EVENT_THREADS);
+
   Event *e = eventAllocator.alloc();
 
   e->init(cont, 0, 0);
-  all_dthreads[n_dthreads] = new EThread(DEDICATED, e);
-  e->ethread               = all_dthreads[n_dthreads];
-  e->mutex = e->continuation->mutex = all_dthreads[n_dthreads]->mutex;
-  n_dthreads++;
+  all_dthreads[n] = new EThread(DEDICATED, e);
+  e->ethread      = all_dthreads[n];
+  e->mutex        = all_dthreads[n]->mutex;
+  cont->mutex     = all_dthreads[n]->mutex;
+
   e->ethread->start(thr_name, stacksize, nullptr, nullptr, nullptr);
 
   return e;

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