[opengl] add TI_WITH_OPENGL env var to disable OpenGL (#962)

taichi/backends/cuda/cuda_driver.cpp

@@ -2,6 +2,7 @@
 
 #include "taichi/system/dynamic_loader.h"
 #include "taichi/backends/cuda/cuda_context.h"
+#include "taichi/util/environ_config.h"
 
 TLANG_NAMESPACE_BEGIN
 
@@ -15,6 +16,8 @@ std::string get_cuda_error_message(uint32 err) {
 }
 
 bool CUDADriver::detected() {
+  if (get_environ_config("TI_ENABLE_CUDA", 1) == 0)
+    return false;
   return loader->loaded();
 }
 

taichi/backends/metal/api.cpp

@@ -1,4 +1,5 @@
 #include "taichi/backends/metal/api.h"
+#include "taichi/util/environ_config.h"
 
 TLANG_NAMESPACE_BEGIN
 
@@ -133,6 +134,8 @@ size_t get_max_total_threads_per_threadgroup(
 
 bool is_metal_api_available() {
 #ifdef TI_PLATFORM_OSX
+  if (get_environ_config("TI_ENABLE_METAL", 1) == 0)
+    return false;
   // If the macOS is provided by a VM (e.g. Travis CI), it's possible that there
   // is no GPU device, so we still have to do a runtime check.
   auto device = mtl_create_system_default_device();

taichi/backends/opengl/opengl_api.cpp

@@ -4,6 +4,7 @@
 #include "taichi/backends/opengl/opengl_kernel_util.h"
 #include "taichi/program/kernel.h"
 #include "taichi/program/program.h"
+#include "taichi/util/environ_config.h"
 
 #ifdef TI_WITH_OPENGL
 #include "glad/glad.h"
@@ -515,6 +516,8 @@ GLSLLaunchGuard::~GLSLLaunchGuard() {
 }
 
 bool is_opengl_api_available() {
+  if (get_environ_config("TI_ENABLE_OPENGL", 1) == 0)
+    return false;
   return initialize_opengl(true);
 }
 

taichi/core/logging.cpp

@@ -155,8 +155,9 @@ std::string signal_name(int sig) {
 bool python_at_exit_called = false;
 
 void signal_handler(int signo) {
-  // It seems that there's no way to pass exception to Python in signal
-  // handlers?
+  // It seems that there's no way to pass exception to Python in signal handlers?
+  // @archibate found that in fact there are such solution:
+  // https://docs.python.org/3/library/faulthandler.html#module-faulthandler
   auto sig_name = signal_name(signo);
   logger.error(fmt::format("Received signal {} ({})", signo, sig_name), false);
   exit(-1);

taichi/util/environ_config.h

@@ -0,0 +1,17 @@
+#pragma once
+
+#include "taichi/common/util.h"
+#include <string>
+#include <cstdlib>
+
+TLANG_NAMESPACE_BEGIN
+
+static inline int get_environ_config(const std::string &name, int default_value = 0)
+{
+  char *res = std::getenv(name.c_str());
+  if (res == nullptr)
+    return default_value;
+  return std::stoi(res);
+}
+
+TLANG_NAMESPACE_END