diff options
| -rw-r--r-- | butl/process.cxx | 101 |
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:: |