On Windows, file handles need to be marked inheritable when they need to
be used as standard input/output/error handles for a newly spawned
process. The problem with that, of course, is that the "inheritable" flag
is global and therefore can wreak havoc with highly multi-threaded
applications: other spawned processes will *also* inherit those file
handles, despite having *other* input/output/error handles, and never
close the former handles because they do not know about them.
Let's introduce a set of environment variables (GIT_REDIRECT_STDIN and
friends) that point to files, or even better, named pipes and that are
used by the spawned Git process. This helps work around above-mentioned
issue: those named pipes will be opened in a non-inheritable way upon
startup, and no handles are passed around.
Signed-off-by: Johannes Schindelin <johannes.schindelin@xxxxxx>
---
compat/mingw.c | 43 +++++++++++++++++++++++++++++++++++++++++++
t/t0001-init.sh | 6 ++++++
2 files changed, 49 insertions(+)
diff --git a/compat/mingw.c b/compat/mingw.c
index 8b6fa0db446..6c6c7795a70 100644
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -2139,6 +2139,47 @@ static char *wcstoutfdup_startup(char *buffer, const wchar_t *wcs, size_t len)
return memcpy(malloc_startup(len), buffer, len);
}
+static void maybe_redirect_std_handle(const wchar_t *key, DWORD std_id, int fd,
+ DWORD desired_access, DWORD flags)
+{
+ DWORD create_flag = fd ? OPEN_ALWAYS : OPEN_EXISTING;
+ wchar_t buf[MAX_PATH];
+ DWORD max = ARRAY_SIZE(buf);
+ HANDLE handle;
+ DWORD ret = GetEnvironmentVariableW(key, buf, max);
+
+ if (!ret || ret >= max)
+ return;
+
+ /* make sure this does not leak into child processes */
+ SetEnvironmentVariableW(key, NULL);
+ if (!wcscmp(buf, L"off")) {
+ close(fd);
+ handle = GetStdHandle(std_id);
+ if (handle != INVALID_HANDLE_VALUE)
+ CloseHandle(handle);
+ return;
+ }
+ handle = CreateFileW(buf, desired_access, 0, NULL, create_flag,
+ flags, NULL);
+ if (handle != INVALID_HANDLE_VALUE) {
+ int new_fd = _open_osfhandle((intptr_t)handle, O_BINARY);
+ SetStdHandle(std_id, handle);
+ dup2(new_fd, fd);
+ close(new_fd);
+ }
+}
+
+static void maybe_redirect_std_handles(void)
+{
+ maybe_redirect_std_handle(L"GIT_REDIRECT_STDIN", STD_INPUT_HANDLE, 0,
+ GENERIC_READ, FILE_ATTRIBUTE_NORMAL);
+ maybe_redirect_std_handle(L"GIT_REDIRECT_STDOUT", STD_OUTPUT_HANDLE, 1,
+ GENERIC_WRITE, FILE_ATTRIBUTE_NORMAL);
+ maybe_redirect_std_handle(L"GIT_REDIRECT_STDERR", STD_ERROR_HANDLE, 2,
+ GENERIC_WRITE, FILE_FLAG_NO_BUFFERING);
+}
+
void mingw_startup(void)
{
int i, maxlen, argc;
@@ -2146,6 +2187,8 @@ void mingw_startup(void)
wchar_t **wenv, **wargv;
_startupinfo si;
+ maybe_redirect_std_handles();
+
/* get wide char arguments and environment */
si.newmode = 0;
if (__wgetmainargs(&argc, &wargv, &wenv, _CRT_glob, &si) < 0)
diff --git a/t/t0001-init.sh b/t/t0001-init.sh
index 86c1a51654f..0fd2fc45385 100755
--- a/t/t0001-init.sh
+++ b/t/t0001-init.sh
@@ -453,4 +453,10 @@ test_expect_success 're-init from a linked worktree' '
)
'
+test_expect_success MINGW 'redirect std handles' '
+ GIT_REDIRECT_STDOUT=output.txt git rev-parse --git-dir &&
+ test .git = "$(cat output.txt)" &&
+ test -z "$(GIT_REDIRECT_STDOUT=off git rev-parse --git-dir)"
+'
+
test_done
--
2.15.0.windows.1
