Fixed a race condition that could cause ProcessGDBRemote::DoResume() to return

an error saying the resume timed out. Previously the thread that was trying
to resume the process would eventually call ProcessGDBRemote::DoResume() which
would broadcast an event over to the async GDB remote thread which would sent the
continue packet to the remote gdb server. Right after this was sent, it would
set a predicate boolean value (protected by a mutex and condition) and then the
thread that issued the ProcessGDBRemote::DoResume() would then wait for that
condition variable to be set. If the async gdb thread was too quick though, the
predicate boolean value could have been set to true and back to false by the
time the thread that issued the ProcessGDBRemote::DoResume() checks the boolean
value. So we can't use the predicate value as a handshake. I have changed the code
over to using a Event by having the GDB remote communication object post an
event: 

	GDBRemoteCommunication::eBroadcastBitRunPacketSent

This allows reliable handshaking between the two threads and avoids the erroneous
ProcessGDBRemote::DoResume() errors.

Added a host backtrace service to allow in process backtraces when trying to track
down tricky issues. I need to see if LLVM has any backtracing abilities abstracted
in it already, and if so, use that, but I needed something ASAP for the current issue
I was working on. The static function is:

void
Host::Backtrace (Stream &strm, uint32_t max_frames);

And it will backtrace at most "max_frames" frames for the current thread and can be
used with any of the Stream subclasses for logging.

llvm-svn: 120793

3 files changed, 22 insertions, 24 deletions

diff --git a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunication.cpp b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunication.cpp
index 89b723849fc..394b55231a8 100644
--- a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunication.cpp
+++ b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunication.cpp
@@ -199,13 +199,13 @@ GDBRemoteCommunication::SendContinuePacketAndWaitForResponse
         log->Printf ("GDBRemoteCommunication::%s ()", __FUNCTION__);
 
     Mutex::Locker locker(m_sequence_mutex);
-//    ScopedValueChanger<bool> restore_running_to_false (m_is_running, false);
     StateType state = eStateRunning;
 
     if (SendPacket(payload, packet_length) == 0)
         state = eStateInvalid;
 
-    m_is_running.SetValue (true, eBroadcastAlways);
+    BroadcastEvent(eBroadcastBitRunPacketSent, NULL);
+    m_is_running.SetValue (true, eBroadcastNever);
 
     while (state == eStateRunning)
     {
@@ -357,7 +357,7 @@ GDBRemoteCommunication::SendContinuePacketAndWaitForResponse
     if (log)
         log->Printf ("GDBRemoteCommunication::%s () => %s", __FUNCTION__, StateAsCString(state));
     response.SetFilePos(0);
-    m_is_running.SetValue (false, eBroadcastOnChange);
+    m_is_running.SetValue (false, eBroadcastAlways);
     return state;
 }
 
@@ -858,16 +858,3 @@ GDBRemoteCommunication::DeallocateMemory (addr_t addr, uint32_t timeout_seconds)
     return false;
 }
 
-bool
-GDBRemoteCommunication::WaitForIsRunning (uint32_t timeout_sec)
-{
-    TimeValue timeout;
-    if (timeout_sec)
-    {
-        timeout = TimeValue::Now();
-        timeout.OffsetWithSeconds (timeout_sec);
-    }
-    return m_is_running.WaitForValueEqualTo (true, &timeout, NULL);
-}
-    
-
diff --git a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunication.h b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunication.h
index e7ef38ab1e0..0434d8fb736 100644
--- a/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunication.h
+++ b/lldb/source/Plugins/Process/gdb-remote/GDBRemoteCommunication.h
@@ -34,6 +34,10 @@ class GDBRemoteCommunication :
     public lldb_private::Communication
 {
 public:
+    enum
+    {
+        eBroadcastBitRunPacketSent = kLoUserBroadcastBit
+    };
     //------------------------------------------------------------------
     // Constructors and Destructors
     //------------------------------------------------------------------
@@ -203,9 +207,6 @@ public:
     }
     
     bool
-    WaitForIsRunning (uint32_t timeout_sec);
-    
-    bool
     GetHostInfo (uint32_t timeout_seconds);
 
     bool 
diff --git a/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp b/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp
index e7a879bd5a5..083ef95a1f6 100644
--- a/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp
+++ b/lldb/source/Plugins/Process/gdb-remote/ProcessGDBRemote.cpp
@@ -878,10 +878,20 @@ ProcessGDBRemote::DoResume ()
 {
     Error error;
     ProcessGDBRemoteLog::LogIf (GDBR_LOG_PROCESS, "ProcessGDBRemote::Resume()");
-    m_async_broadcaster.BroadcastEvent (eBroadcastBitAsyncContinue, new EventDataBytes (m_continue_packet.GetData(), m_continue_packet.GetSize()));
-    const uint32_t timedout_sec = 1;
-    if (m_gdb_comm.WaitForIsRunning (timedout_sec) == false)
-        error.SetErrorString("Resume timed out.");
+    
+    Listener listener ("gdb-remote.resume-packet-sent");
+    if (listener.StartListeningForEvents (&m_gdb_comm, GDBRemoteCommunication::eBroadcastBitRunPacketSent))
+    {
+        EventSP event_sp;
+        TimeValue timeout;
+        timeout = TimeValue::Now();
+        timeout.OffsetWithSeconds (5);
+        m_async_broadcaster.BroadcastEvent (eBroadcastBitAsyncContinue, new EventDataBytes (m_continue_packet.GetData(), m_continue_packet.GetSize()));
+
+        if (listener.WaitForEvent (&timeout, event_sp) == false)
+            error.SetErrorString("Resume timed out.");
+    }
+
     return error;
 }
 
@@ -1206,7 +1216,7 @@ ProcessGDBRemote::DoDestroy ()
     SetExitStatus(-1, "process killed");
 
     StringExtractorGDBRemote response;
-    if (m_gdb_comm.SendPacketAndWaitForResponse("k", response, 2, false))
+    if (m_gdb_comm.SendPacketAndWaitForResponse("k", response, 1, false))
     {
         log = ProcessGDBRemoteLog::GetLogIfAllCategoriesSet(GDBR_LOG_PROCESS);
         if (log)