Add alternate paths for the tuning file on Android

cross-files/aarch64-linux-android

@@ -13,7 +13,7 @@ endian = 'little'
 
 [properties]
 needs_exe_wrapper = true
-cpp_args = ['-Dandroid']
+cpp_args = []
 cpp_link_args = ['-llog', '-static-libstdc++']
 
 [binaries]

cross-files/armv7a-linux-androideabi

@@ -16,7 +16,7 @@ endian = 'little'
 
 [properties]
 needs_exe_wrapper = true
-cpp_args = ['-Dandroid']
+cpp_args = []
 cpp_link_args = ['-llog', '-static-libstdc++']
 
 [binaries]

src/neural/opencl/OpenCLTuner.cc

@@ -28,19 +28,16 @@
 #include <random>
 #include <sstream>
 #include <string>
+#include <unistd.h>
 
 #include "neural/opencl/OpenCL.h"
 #include "neural/opencl/OpenCLParams.h"
 #include "neural/opencl/OpenCLTuner.h"
 
 #include "utils/logging.h"
+#include "utils/commandline.h"
 
-// Use the temporary directory on Android as the engine may run with restricted file access
-#ifdef android
-const auto TUNER_FILE_LOCAL = std::string("/data/local/tmp/leelaz_opencl_tuning");
-#else
 const auto TUNER_FILE_LOCAL = std::string("leelaz_opencl_tuning");
-#endif
 
 constexpr auto MAX_ERROR = 1e-4f;
 
@@ -372,20 +369,41 @@ std::string Tuner::tune_sgemm(const int m, const int n, const int k,
   return best_params;
 }
 
+const std::string leelaz_file(std::string file) {
+// On Android, the engine may run with restricted file access. The ideal place to store
+// the tuning file should be the Android Context.getFilesDir(). But such context is hard
+// to get from here. As an alternative, the current directory is tried if it's writeable.
+// Else the binary directory is used, hoping that the engine was installed to a writable
+// directory.
+#ifdef __ANDROID__
+  std::string path;
+  char buffer[PATH_MAX];
+  const char* current_directory = getcwd(buffer, sizeof(buffer));
+  if (access(current_directory, W_OK) == 0) {
+    path = current_directory;
+  } else {
+    path = lczero::CommandLine::BinaryDirectory();
+  }  
+  return path + "/" + file;
+#else
+  return file;
+#endif  
+}
+
 void Tuner::store_sgemm_tuners(const int m, const int n, const int k,
                                const int batch_size, std::string tuners) {
   auto file_contents = std::vector<std::string>();
   {
     // Read the previous contents to string.
-    auto file = std::ifstream{TUNER_FILE_LOCAL};
+    auto file = std::ifstream{leelaz_file(TUNER_FILE_LOCAL)};
     if (file.good()) {
       auto line = std::string{};
       while (std::getline(file, line)) {
         file_contents.emplace_back(line);
       }
     }
   }
-  auto file = std::ofstream{TUNER_FILE_LOCAL};
+  auto file = std::ofstream{leelaz_file(TUNER_FILE_LOCAL)};  
 
   auto device_name = m_opencl.get_device_name();
   auto tuning_params = std::stringstream{};
@@ -409,7 +427,7 @@ void Tuner::store_sgemm_tuners(const int m, const int n, const int k,
 
   if (file.fail()) {
     CERR << "Could not save the tuning result.";
-    CERR << "Do I have write permissions on " << TUNER_FILE_LOCAL << "?";
+    CERR << "Do I have write permissions on " << leelaz_file(TUNER_FILE_LOCAL) << "?";
   }
 }
 
@@ -462,7 +480,7 @@ std::string Tuner::sgemm_tuners_from_line(std::string line, const int m,
 std::string Tuner::load_sgemm_tuners(const int m, const int n, const int k,
                                      const int batch_size) {
   if (!m_params.force_tune) {
-    auto file = std::ifstream{TUNER_FILE_LOCAL};
+    auto file = std::ifstream{leelaz_file(TUNER_FILE_LOCAL)};
     if (file.good()) {
       auto line = std::string{};
       while (std::getline(file, line)) {