win: port multiprocess_exec_test_child.cc

util/test/multiprocess_exec_test_child.cc

Index: util/test/multiprocess_exec_test_child.cc
diff --git a/util/test/multiprocess_exec_test_child.cc b/util/test/multiprocess_exec_test_child.cc
index e1a06122ed1779d9cf1d33b125505053c1e1979c..7e8525c67e5ef95c29a2e43d1eac1f25c390d256 100644
--- a/util/test/multiprocess_exec_test_child.cc
+++ b/util/test/multiprocess_exec_test_child.cc
@@ -17,11 +17,19 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <sys/types.h>
-#include <unistd.h>
 
 #include <algorithm>
 
+#include "build/build_config.h"
+
+#if defined(OS_POSIX)
+#include <unistd.h>
+#elif defined(OS_WIN)
+#include <windows.h>
+#endif
+
 int main(int argc, char* argv[]) {
+#if defined(OS_POSIX)
   // Make sure that there’s nothing open at any FD higher than 3. All FDs other
   // than stdin, stdout, and stderr should have been closed prior to or at
   // exec().
@@ -47,5 +55,41 @@ int main(int argc, char* argv[]) {
     abort();
   }
 
+#elif defined(OS_WIN)
+
+  // Make sure there's nothing open other than stdin, stdout, and stderr.
+  HANDLE handle_stdin = GetStdHandle(STD_INPUT_HANDLE);
+  HANDLE handle_stdout = GetStdHandle(STD_OUTPUT_HANDLE);
+  HANDLE handle_stderr = GetStdHandle(STD_ERROR_HANDLE);
+  // Handles can theoretically go as high as 2^32-4, but in practice they're

[Mark Mentovai, 2015/01/08 17:20:20]

I thought Windows had an API to do this a little more gracefully than looping
over things and closing them (honestly, it’s kind of a hack on the POSIX side
too). Can’t we get the system to give us all of the handles that are available
in the process, along the lines of
http://nsylvain.blogspot.com/2007/09/how-list-all-open-handles.html?

[Mark Mentovai, 2015/01/08 17:20:20]

Blank line before the comment, to make it easier to spot that it’s a new
conceptual “thing.”

[scottmg, 2015/01/08 18:15:53]

Sure, I actually used that at first based on
https://code.google.com/p/chromium/codesearch#chromium/src/sandbox/win/sandbo...,
but it seemed a bit heavy. Switched as it is a bit cleaner.

+  // never that large, so we check only up to 2^16.
+  for (uintptr_t handle_int = 4; handle_int <= 0xffff; handle_int += 4) {
+    HANDLE handle = reinterpret_cast<HANDLE>(handle_int);
+    if (handle == handle_stdin || handle == handle_stdout ||
+        handle == handle_stderr)
+      continue;

[Mark Mentovai, 2015/01/08 17:20:20]

{} me (the condition takes up more than one line, so the bracing helps make it
easier to follow through all that ragged indentation).

[scottmg, 2015/01/08 18:15:53]

Removed.

+    if (CloseHandle(handle)) {

[Mark Mentovai, 2015/01/08 17:20:20]

Can CloseHandle() fail for a reason other than an invalid handle?

[scottmg, 2015/01/08 18:15:53]

I don't know of any reason, but there are so many types that I don't know for
sure. The other way should be more robust to that.

+      abort();
+    }
+  }
+
+  // Read a byte from stdin, expecting it to be a specific value.
+  char c;
+  DWORD bytes_read;
+  if (!ReadFile(handle_stdin, &c, 1, &bytes_read, nullptr) || bytes_read != 1 ||
+      c != 'z') {
+    abort();
+  }
+
+  // Write a byte to stdout.
+  c = 'Z';
+  DWORD bytes_written;
+  if (!WriteFile(handle_stdout, &c, 1, &bytes_written, nullptr) ||
+      bytes_written != 1) {
+    abort();
+  }
+
+#endif  // OS_POSIX
+
   return 0;
 }