[PATCH 1/3] mingw: add experimental feature to redirect standard handles
- From
Johannes Schindelin <johannes.schindelin@gmx.de>
- Date
- Oct 30, 2017, 17:10 UTC
- Message-ID
- <804f26293de8f7cf805711313e376a513011a048.1509382976.git.johannes.schindelin@gmx.de>
- In-Reply-To
- <cover.1509382976.git.johannes.schindelin@gmx.de>
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@gmx.de> --- 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