[Lldb-commits] [PATCH] Fix deadlock in operation thread in NativeProcessLinux

[Tamas Berghammer]

Update based on suggestion in comment


http://reviews.llvm.org/D8030

Files:
  source/Plugins/Process/Linux/NativeProcessLinux.cpp

Index: source/Plugins/Process/Linux/NativeProcessLinux.cpp
===================================================================
--- source/Plugins/Process/Linux/NativeProcessLinux.cpp
+++ source/Plugins/Process/Linux/NativeProcessLinux.cpp
@@ -142,6 +142,8 @@
     using namespace lldb;
     using namespace lldb_private;
 
+    static void * const EXIT_OPERATION = nullptr;
+
     const UnixSignals&
     GetUnixSignals ()
     {
@@ -3370,14 +3372,11 @@
             assert(false && "Unexpected errno from sem_wait");
         }
 
-        // nullptr as operation means the operation thread should exit. Cancel() can't be used
-        // because it is not supported on android.
-        if (!monitor->m_operation)
-        {
-            // notify calling thread that operation is complete
-            sem_post(&monitor->m_operation_done);
+        // EXIT_OPERATION used to stop the operation thread because Cancel() isn't supported on
+        // android. We don't have to send a post to the m_operation_done semaphore because in this
+        // case the synchronization is achieved by a Join() call
+        if (monitor->m_operation == EXIT_OPERATION)
             break;
-        }
 
         reinterpret_cast<Operation*>(monitor->m_operation)->Execute(monitor);
 
@@ -3396,12 +3395,17 @@
     // notify operation thread that an operation is ready to be processed
     sem_post(&m_operation_pending);
 
-    // wait for operation to complete
-    while (sem_wait(&m_operation_done))
+    // Don't wait for the operation to complete in case of an exit operation. The operation thread
+    // will exit without posting to the semaphore
+    if (m_operation != EXIT_OPERATION)
     {
-        if (errno == EINTR)
-            continue;
-        assert(false && "Unexpected errno from sem_wait");
+        // wait for operation to complete
+        while (sem_wait(&m_operation_done))
+        {
+            if (errno == EINTR)
+                continue;
+            assert(false && "Unexpected errno from sem_wait");
+        }
     }
 }
 
@@ -3564,9 +3568,9 @@
 void
 NativeProcessLinux::StopMonitor()
 {
-    StopOpThread();
     StopMonitoringChildProcess();
     StopCoordinatorThread ();
+    StopOpThread();
     sem_destroy(&m_operation_pending);
     sem_destroy(&m_operation_done);
 
@@ -3583,7 +3587,7 @@
     if (!m_operation_thread.IsJoinable())
         return;
 
-    DoOperation(nullptr); // nullptr as operation ask the operation thread to exit
+    DoOperation(EXIT_OPERATION);
     m_operation_thread.Join(nullptr);
 }

EMAIL PREFERENCES
  http://reviews.llvm.org/settings/panel/emailpreferences/
-------------- next part --------------
A non-text attachment was scrubbed...
Name: D8030.21098.patch
Type: text/x-patch
Size: 2545 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/lldb-commits/attachments/20150303/f1d174a5/attachment.bin>