Work around buggy OpenCL ICD loader

ocl-icd under 2.2.3 calls dlopen() in its library constructor
and accesses a thread local variable in the process. This causes
all subsequent access to any other thread local variables to
deadlock.

The bug is fixed in ocl-icd 2.2.4, which is not in stable releases
in Ubuntu or Debian. Thus this provides a workaround given buggy
ocl-icd.

To avoid access to thread local variable, errno, std::ostream
with unitbuf, and exception handling in libstdc++ cannot be used.

This commit checks ocl-icd version, and refactor the OpenCL
processor to not use exceptions. Then disable unitbuf on std::cerr
and disable all exceptions with -fno-exceptions (when available).

This commit and the ocl-icd bug do not affect Mac OS X or Windows.

Author: xlz

examples/protonect/CMakeLists.txt

@@ -166,6 +166,13 @@ IF(ENABLE_OPENCL)
     LIST(APPEND RESOURCES
       src/opencl_depth_packet_processor.cl
     )
+
+    # Major Linux distro stable releases have buggy OpenCL ICD loader.
+    # The workaround of disabling exceptions can only be set up during compile time.
+    # Diabling it for all should be harmless. The flag is the same for GCC/Clang/ICC.
+    IF(UNIX AND NOT APPLE)
+      SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fno-exceptions")
+    ENDIF()
   ENDIF(OPENCL_FOUND)
 ENDIF(ENABLE_OPENCL)
 

examples/protonect/src/logging.cpp

@@ -97,6 +97,12 @@ class ConsoleLogger : public Logger
   ConsoleLogger(Level level)
   {
     level_ = level;
+    //std::ios_base::unitbuf causes automatic flushing which access
+    //thread local variable via std::uncaught_exception().
+    //This causes deadlock with ocl-icd until its recent update.
+    //Accessing TLS has a slight performance penalty.
+    //log() always flush the ostream so unitbuf is unnecessary anyway.
+    std::nounitbuf(std::cerr);
   }
   virtual ~ConsoleLogger() {}
   virtual void log(Level level, const std::string &message)