Index: lldb/trunk/source/Host/common/Host.cpp
===================================================================
--- lldb/trunk/source/Host/common/Host.cpp
+++ lldb/trunk/source/Host/common/Host.cpp
@@ -113,7 +113,7 @@
     return ThreadLauncher::LaunchThread(thread_name, MonitorChildProcessThreadFunction, info_ptr, NULL);
 }
 
-#if !defined(__ANDROID__) && !defined(__ANDROID_NDK__)
+#ifndef __linux__
 //------------------------------------------------------------------
 // Scoped class that will disable thread canceling when it is
 // constructed, and exception safely restore the previous value it
@@ -140,7 +140,32 @@
 private:
     int m_old_state;    // Save the old cancelability state.
 };
-#endif // __ANDROID_NDK__
+#endif // __linux__
+
+#ifdef __linux__
+static thread_local volatile sig_atomic_t g_usr1_called;
+
+static void
+SigUsr1Handler (int)
+{
+    g_usr1_called = 1;
+}
+#endif // __linux__
+
+static bool
+CheckForMonitorCancellation()
+{
+#ifdef __linux__
+    if (g_usr1_called)
+    {
+        g_usr1_called = 0;
+        return true;
+    }
+#else
+    ::pthread_testcancel ();
+#endif
+    return false;
+}
 
 static thread_result_t
 MonitorChildProcessThreadFunction (void *arg)
@@ -167,21 +192,29 @@
 #endif
     const int options = __WALL;
 
+#ifdef __linux__
+    // This signal is only used to interrupt the thread from waitpid
+    struct sigaction sigUsr1Action;
+    memset(&sigUsr1Action, 0, sizeof(sigUsr1Action));
+    sigUsr1Action.sa_handler = SigUsr1Handler;
+    ::sigaction(SIGUSR1, &sigUsr1Action, nullptr);
+#endif // __linux__    
+
     while (1)
     {
         log = lldb_private::GetLogIfAllCategoriesSet (LIBLLDB_LOG_PROCESS);
         if (log)
             log->Printf("%s ::waitpid (pid = %" PRIi32 ", &status, options = %i)...", function, pid, options);
 
-        // Wait for all child processes
-#if !defined(__ANDROID__) && !defined(__ANDROID_NDK__)
-        ::pthread_testcancel ();
-#endif
+        if (CheckForMonitorCancellation ())
+            break;
+
         // Get signals from all children with same process group of pid
         const ::pid_t wait_pid = ::waitpid (pid, &status, options);
-#if !defined(__ANDROID__) && !defined(__ANDROID_NDK__)
-        ::pthread_testcancel ();
-#endif
+
+        if (CheckForMonitorCancellation ())
+            break;
+
         if (wait_pid == -1)
         {
             if (errno == EINTR)
@@ -226,7 +259,7 @@
 
             // Scope for pthread_cancel_disabler
             {
-#if !defined(__ANDROID__) && !defined(__ANDROID_NDK__)
+#ifndef __linux__
                 ScopedPThreadCancelDisabler pthread_cancel_disabler;
 #endif
 
Index: lldb/trunk/source/Plugins/Process/Linux/NativeProcessLinux.h
===================================================================
--- lldb/trunk/source/Plugins/Process/Linux/NativeProcessLinux.h
+++ lldb/trunk/source/Plugins/Process/Linux/NativeProcessLinux.h
@@ -257,7 +257,7 @@
             Error &error);
 
         /// Attaches to an existing process.  Forms the
-        /// implementation of Process::DoLaunch.
+        /// implementation of Process::DoAttach
         void
         AttachToInferior (lldb::pid_t pid, Error &error);
 
@@ -317,7 +317,7 @@
 
         /// Stops the child monitor thread.
         void
-        StopMonitoringChildProcess();
+        StopMonitorThread();
 
         /// Stops the operation thread used to attach/launch a process.
         void
Index: lldb/trunk/source/Plugins/Process/Linux/NativeProcessLinux.cpp
===================================================================
--- lldb/trunk/source/Plugins/Process/Linux/NativeProcessLinux.cpp
+++ lldb/trunk/source/Plugins/Process/Linux/NativeProcessLinux.cpp
@@ -35,11 +35,12 @@
 #include "lldb/Core/RegisterValue.h"
 #include "lldb/Core/Scalar.h"
 #include "lldb/Core/State.h"
+#include "lldb/Host/common/NativeRegisterContext.h"
 #include "lldb/Host/Host.h"
 #include "lldb/Host/HostInfo.h"
+#include "lldb/Host/HostNativeThread.h"
 #include "lldb/Host/ThreadLauncher.h"
 #include "lldb/Symbol/ObjectFile.h"
-#include "lldb/Host/common/NativeRegisterContext.h"
 #include "lldb/Target/Process.h"
 #include "lldb/Target/ProcessLaunchInfo.h"
 #include "lldb/Utility/PseudoTerminal.h"
@@ -3557,11 +3558,11 @@
 }
 
 void
-NativeProcessLinux::StopMonitoringChildProcess()
+NativeProcessLinux::StopMonitorThread()
 {
     if (m_monitor_thread.IsJoinable())
     {
-        m_monitor_thread.Cancel();
+        ::pthread_kill(m_monitor_thread.GetNativeThread().GetSystemHandle(), SIGUSR1);
         m_monitor_thread.Join(nullptr);
     }
 }
@@ -3569,7 +3570,7 @@
 void
 NativeProcessLinux::StopMonitor()
 {
-    StopMonitoringChildProcess();
+    StopMonitorThread();
     StopCoordinatorThread ();
     StopOpThread();
     sem_destroy(&m_operation_pending);
Index: lldb/trunk/source/Plugins/Process/Linux/ProcessMonitor.cpp
===================================================================
--- lldb/trunk/source/Plugins/Process/Linux/ProcessMonitor.cpp
+++ lldb/trunk/source/Plugins/Process/Linux/ProcessMonitor.cpp
@@ -24,6 +24,7 @@
 #include "lldb/Core/RegisterValue.h"
 #include "lldb/Core/Scalar.h"
 #include "lldb/Host/Host.h"
+#include "lldb/Host/HostNativeThread.h"
 #include "lldb/Host/HostThread.h"
 #include "lldb/Host/ThreadLauncher.h"
 #include "lldb/Target/Thread.h"
@@ -94,6 +95,8 @@
 
 using namespace lldb_private;
 
+static Operation* EXIT_OPERATION = nullptr;
+
 // FIXME: this code is host-dependent with respect to types and
 // endianness and needs to be fixed.  For example, lldb::addr_t is
 // hard-coded to uint64_t, but on a 32-bit Linux host, ptrace requires
@@ -2335,7 +2338,7 @@
 {
     if (m_monitor_thread.IsJoinable())
     {
-        m_monitor_thread.Cancel();
+        ::pthread_kill(m_monitor_thread.GetNativeThread().GetSystemHandle(), SIGUSR1);
         m_monitor_thread.Join(nullptr);
     }
 }
@@ -2359,6 +2362,6 @@
     if (!m_operation_thread.IsJoinable())
         return;
 
-    m_operation_thread.Cancel();
+    DoOperation(EXIT_OPERATION);
     m_operation_thread.Join(nullptr);
 }