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-rw-r--r--butl/process.cxx101
1 files changed, 82 insertions, 19 deletions
diff --git a/butl/process.cxx b/butl/process.cxx
index c0355d4..db529a6 100644
--- a/butl/process.cxx
+++ b/butl/process.cxx
@@ -1115,31 +1115,94 @@ namespace butl
in == STDERR_FILENO)
fail ("invalid file descriptor");
- if (!CreateProcess (
- batch != nullptr ? batch : pp.effect_string (),
- const_cast<char*> (cmd_line.c_str ()),
- 0, // Process security attributes.
- 0, // Primary thread security attributes.
- true, // Inherit handles.
- 0, // Creation flags.
- 0, // Use our environment.
- cwd != nullptr && *cwd != '\0' ? cwd : nullptr,
- &si,
- &pi))
- fail ();
- } // Revert handled back to non-inheritable and release the lock.
-
- auto_handle (pi.hThread).reset (); // Close.
+ // Ready for some "Fun with Windows"(TM)? Here is what's in today's
+ // episode: MSYS2 (actually, Cygwin) tries to emulate POSIX fork() on
+ // Win32 via some pretty heavy hackery. As a result it makes a bunch of
+ // assumptions such as that the child process will have the same virtual
+ // memory position as the parent and that nobody interferes in its
+ // child-parent dance.
+ //
+ // This, however, doesn't always pan out: for reasons unknown Windows
+ // sometimes decides to start the child somewhere else (or, as Cygwin
+ // FAQ puts it: "sometimes Windows sets up a process environment that is
+ // even more hostile to fork() than usual"). Also things like Windows
+ // Defender (collectively called Big List Of Dodgy Apps/BLODA in Cygwin
+ // speak) do interfere in all kinds of ways.
+ //
+ // We also observe another issue that seem related: if we run multiple
+ // MSYS2-based applications in parallel (either from the same process
+ // or from several processes), then they sometimes terminate abnormally
+ // (but quietly, without printing any of the cygheap/fork diagnostics)
+ // with status 0xC0000142 (STATUS_DLL_INIT_FAILED).
+ //
+ // Cygwin FAQ suggests the following potential solutions:
+ //
+ // 1. Restart the process hoping things will pan out next time around.
+ //
+ // 2. Eliminate/disable programs from BLODA (disabling Defender helps
+ // a lot but not entirely).
+ //
+ // 3. Apparently switching from 32 to 64-bit should help (less chance
+ // for address collisions).
+ //
+ // 4. Rebase all the Cygwin DLLs (this is a topic for a another episode).
+ //
+ // To add to this list, we also have our own remedy (which is not
+ // generally applicable):
+ //
+ // 5. Make sure processes that you start don't need to fork. A good
+ // example would be tar that runs gz/bzip2/xz. Instead, we start and
+ // pipe them ourselves.
+ //
+ // So what's coming next is a hack that implements remedy #1: after
+ // starting the process we wait a bit (50ms) and check if it has
+ // terminated with STATUS_DLL_INIT_FAILED (the assumption here is that
+ // if this happens, it happens quickly). We then retry starting the
+ // process for up to a second.
+ //
+ // One way to improve this implementation would be to only do it for
+ // MSYS2-based programs, for example, by checking (EnumProcessModules())
+ // if the process loaded the msys-2.0.dll (not clear though if it will
+ // be in the returned list if it has failed to initialize). With this
+ // improvement we could then wait longer and try harder.
+ //
+ for (size_t ret (0); ret != 20; ++ret)
+ {
+ if (!CreateProcess (
+ batch != nullptr ? batch : pp.effect_string (),
+ const_cast<char*> (cmd_line.c_str ()),
+ 0, // Process security attributes.
+ 0, // Primary thread security attributes.
+ true, // Inherit handles.
+ 0, // Creation flags.
+ 0, // Use our environment.
+ cwd != nullptr && *cwd != '\0' ? cwd : nullptr,
+ &si,
+ &pi))
+ fail ();
- this->out_fd = move (out_fd.out);
- this->in_ofd = move (in_ofd.in);
- this->in_efd = move (in_efd.in);
+ auto_handle (pi.hThread).reset (); // Close.
- this->handle = pi.hProcess;
+ // Wait a bit (50ms) and check if the process has terminated. If it is
+ // still running then we assume all is good. Otherwise, retry if this
+ // is the DLL initialization error.
+ //
+ DWORD s;
+ if (WaitForSingleObject (pi.hProcess, 50) != WAIT_OBJECT_0 ||
+ !GetExitCodeProcess (pi.hProcess, &s) ||
+ s != STATUS_DLL_INIT_FAILED)
+ break;
+ }
+ } // Revert handles back to non-inheritable and release the lock.
// 0 has a special meaning denoting a terminated process handle.
//
+ this->handle = pi.hProcess;
assert (this->handle != 0 && this->handle != INVALID_HANDLE_VALUE);
+
+ this->out_fd = move (out_fd.out);
+ this->in_ofd = move (in_ofd.in);
+ this->in_efd = move (in_efd.in);
}
bool process::