Fix sycl-ls on windows

sycl/tools/sycl-ls/sycl-ls.cpp

@@ -24,6 +24,11 @@
 #include <stdlib.h>
 #include <vector>
 
+#ifdef _WIN32
+#include <system_error>
+#include <windows.h>
+#endif
+
 using namespace sycl;
 using namespace std::literals;
 
@@ -196,6 +201,53 @@ static void unsetFilterEnvVars() {
   }
 }
 
+/* On Windows, the sycl-ls executable and sycl DLL have different copies
+ *  of environment variables. So, just unsetting device filter env. vars
+ *  in sycl-ls won't reflect in sycl DLL. Therefore, on Windows, after
+ *  unsetting env. variables in the parent process, we spawn a child
+ *  sycl-ls process that inherits parents envirnonment.
+ */
+#ifdef _WIN32
+static int unsetFilterEnvVarsAndFork() {
+  // Unset all device filter enviornment variable.
+  unsetFilterEnvVars();
+
+  // Create a new sycl-ls process.
+  STARTUPINFO si;
+  memset(&si, 0, sizeof(si));
+  si.cb = sizeof(si);
+  // Redirect child process's stdout and stderr outputs to parent process.
+  si.hStdOutput = GetStdHandle(STD_OUTPUT_HANDLE);
+  si.hStdError = GetStdHandle(STD_ERROR_HANDLE);
+  si.dwFlags |= STARTF_USESTDHANDLES;
+
+  PROCESS_INFORMATION pi;
+  if (!CreateProcess(NULL,             /* Applicatioon name. */
+                     GetCommandLine(), /* Current process's CLI input. */
+                     NULL,             /* Inherit security attributes. */
+                     NULL,             /* Thread security attributes. */
+                     TRUE,             /* Inherit handles from parent proc.*/
+                     0,                /* Creation flags. */
+                     NULL,             /* Inherit env. block from parent.*/
+                     NULL,             /* Inherit current directory. */
+                     &si, &pi)) {
+    // Unable to create a process. Print error message and abort.
+    std::string message = std::system_category().message(GetLastError());
+    std::cerr << message.c_str() << std::endl;
+
+    std::cerr << "Error creating a new sycl-ls process. Aborting!" << std::endl;
+    return EXIT_FAILURE;
+  }
+
+  // Wait for child process to finish.
+  WaitForSingleObject(pi.hProcess, INFINITE);
+
+  CloseHandle(pi.hProcess);
+  CloseHandle(pi.hThread);
+  return EXIT_SUCCESS;
+}
+#endif
+
 int main(int argc, char **argv) {
 
   if (argc == 1) {
@@ -218,9 +270,18 @@ int main(int argc, char **argv) {
   // the filter environment variable is set.
   printWarningIfFiltersUsed(SuppressNumberPrinting);
 
+  // On Windows, to print all devices available on the system,
+  // we spawn a child sycl-ls process with all device filter
+  // environment variables unset.
+#ifdef _WIN32
+  if (DiscardFilters && FilterEnvVars.size()) {
+    return unsetFilterEnvVarsAndFork();
+  }
+#endif
+
   try {
     // Unset all filter env. vars to get all available devices in the system.
-    if (DiscardFilters)
+    if (DiscardFilters && FilterEnvVars.size())
       unsetFilterEnvVars();
 
     const auto &Platforms = platform::get_platforms();