From 448da22f20b4893f605095015bcc7dd092ad1fe3 Mon Sep 17 00:00:00 2001
From: Justin Lewis Salmon <jsalmon@cern.ch>
Date: Fri, 26 Apr 2013 16:00:38 +0100
Subject: [PATCH] Use cleanup handler in mac-specific semaphore implementation
 to allow its condition variable to be unlocked on thread cancellation

---
 src/XrdSys/XrdSysPthread.cc | 23 +++++++++++++++++++----
 src/XrdSys/XrdSysPthread.hh |  2 ++
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/src/XrdSys/XrdSysPthread.cc b/src/XrdSys/XrdSysPthread.cc
index 2ada1766175..752fafb18b7 100644
--- a/src/XrdSys/XrdSysPthread.cc
+++ b/src/XrdSys/XrdSysPthread.cc
@@ -220,10 +220,14 @@ void XrdSysSemaphore::Post()
 void XrdSysSemaphore::Wait()
 {
 
-// Wait until the sempahore value is positive. This will not be starvation
-// free is the OS implements an unfair mutex;
+// Wait until the semaphore value is positive. This will not be starvation
+// free if the OS implements an unfair mutex.
+// Adding a cleanup handler to the stack here enables threads using this OSX
+// semaphore to be canceled (which is rare). A scoped lock won't work here
+// because OSX is broken and doesn't call destructors properly.
 //
-   XrdSysCondVarHelper scopedLock(&semVar);
+   semVar.Lock();
+   pthread_cleanup_push(&XrdSysSemaphore::CleanUp, (void *) &semVar);
    if (semVal < 1 || semWait)
       while(semVal < 1)
            {semWait++;
@@ -231,9 +235,20 @@ void XrdSysSemaphore::Wait()
             semWait--;
            }
 
-// Decrement the semaphore value and return
+// Decrement the semaphore value, unlock the underlying cond var and return
 //
    semVal--;
+   pthread_cleanup_pop(1);
+}
+
+/******************************************************************************/
+/*                               C l e a n U p                                */
+/******************************************************************************/
+
+void XrdSysSemaphore::CleanUp(void *semVar)
+{
+  XrdSysCondVar *sv = (XrdSysCondVar *) semVar;
+  sv->UnLock();
 }
 #endif
  
diff --git a/src/XrdSys/XrdSysPthread.hh b/src/XrdSys/XrdSysPthread.hh
index 1a1338e9e68..5132530098d 100644
--- a/src/XrdSys/XrdSysPthread.hh
+++ b/src/XrdSys/XrdSysPthread.hh
@@ -311,6 +311,8 @@ public:
 
        void Wait();
 
+static void CleanUp(void *semVar);
+
   XrdSysSemaphore(int semval=1,const char *cid=0) : semVar(0, cid)
                                   {semVal = semval; semWait = 0;}
  ~XrdSysSemaphore() {}