Merge pull request #1170 from dscho/mingw-kill-process

Handle Ctrl+C in Git Bash nicely

Author: Git for Windows Build Agent

compat/mingw.c

@@ -6,6 +6,7 @@
 #include "../strbuf.h"
 #include "../run-command.h"
 #include "../cache.h"
+#include "win32/exit-process.h"
 
 #define HCAST(type, handle) ((type)(intptr_t)handle)
 
@@ -1498,10 +1499,43 @@ struct pinfo_t {
 static struct pinfo_t *pinfo = NULL;
 CRITICAL_SECTION pinfo_cs;
 
+#ifndef SIGRTMAX
+#define SIGRTMAX 63
+#endif
+
+static void kill_child_processes_on_signal(void)
+{
+	DWORD status;
+
+	/*
+	 * Only continue if the process was terminated by a signal, as
+	 * indicated by the exit status (128 + sig_no).
+	 *
+	 * As we are running in an atexit() handler, the exit code has been
+	 * set at this stage by the ExitProcess() function already.
+	 */
+	if (!GetExitCodeProcess(GetCurrentProcess(), &status) ||
+	    status <= 128 || status > 128 + SIGRTMAX)
+		return;
+
+	EnterCriticalSection(&pinfo_cs);
+
+	while (pinfo) {
+		struct pinfo_t *info = pinfo;
+		pinfo = pinfo->next;
+		exit_process(info->proc, status);
+		CloseHandle(info->proc);
+		free(info);
+	}
+
+	LeaveCriticalSection(&pinfo_cs);
+}
+
 static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **deltaenv,
 			      const char *dir,
 			      int prepend_cmd, int fhin, int fhout, int fherr)
 {
+	static int atexit_handler_initialized;
 	STARTUPINFOW si;
 	PROCESS_INFORMATION pi;
 	struct strbuf args;
@@ -1511,6 +1545,17 @@ static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **deltaen
 	HANDLE cons;
 	const char *strace_env;
 
+	if (!atexit_handler_initialized) {
+		atexit_handler_initialized = 1;
+		/*
+		 * On Windows, there is no POSIX signaling. Instead, we inject
+		 * a thread calling ExitProcess(128 + sig_no); and that calls
+		 * the *atexit* handlers. Catch this condition and kill child
+		 * processes with the same signal.
+		 */
+		atexit(kill_child_processes_on_signal);
+	}
+
 	do_unset_environment_variables();
 
 	/* Determine whether or not we are associated to a console */
@@ -1752,16 +1797,27 @@ int mingw_execvp(const char *cmd, char *const *argv)
 int mingw_kill(pid_t pid, int sig)
 {
 	if (pid > 0 && sig == SIGTERM) {
-		HANDLE h = OpenProcess(PROCESS_TERMINATE, FALSE, pid);
-
-		if (TerminateProcess(h, -1)) {
-			CloseHandle(h);
-			return 0;
+		HANDLE h = OpenProcess(PROCESS_CREATE_THREAD |
+				       PROCESS_QUERY_INFORMATION |
+				       PROCESS_VM_OPERATION | PROCESS_VM_WRITE |
+				       PROCESS_VM_READ | PROCESS_TERMINATE,
+				       FALSE, pid);
+		int ret;
+
+		if (h)
+			ret = exit_process(h, 128 + sig);
+		else {
+			h = OpenProcess(PROCESS_TERMINATE, FALSE, pid);
+			if (!h) {
+				errno = err_win_to_posix(GetLastError());
+				return -1;
+			}
+			ret = terminate_process_tree(h, 128 + sig);
 		}
-
-		errno = err_win_to_posix(GetLastError());
 		CloseHandle(h);
-		return -1;
+		if (ret)
+			errno = err_win_to_posix(GetLastError());
+		return ret;
 	} else if (pid > 0 && sig == 0) {
 		HANDLE h = OpenProcess(PROCESS_QUERY_INFORMATION, FALSE, pid);
 		if (h) {

compat/win32/exit-process.h

@@ -0,0 +1,160 @@
+#ifndef EXIT_PROCESS_H
+#define EXIT_PROCESS_H
+
+/*
+ * This file contains functions to terminate a Win32 process, as gently as
+ * possible.
+ *
+ * At first, we will attempt to inject a thread that calls ExitProcess(). If
+ * that fails, we will fall back to terminating the entire process tree.
+ *
+ * For simplicity, these functions are marked as file-local.
+ */
+
+#include <tlhelp32.h>
+
+/*
+ * Terminates the process corresponding to the process ID and all of its
+ * directly and indirectly spawned subprocesses.
+ *
+ * This way of terminating the processes is not gentle: the processes get
+ * no chance of cleaning up after themselves (closing file handles, removing
+ * .lock files, terminating spawned processes (if any), etc).
+ */
+static int terminate_process_tree(HANDLE main_process, int exit_status)
+{
+	HANDLE snapshot = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0);
+	PROCESSENTRY32 entry;
+	DWORD pids[16384];
+	int max_len = sizeof(pids) / sizeof(*pids), i, len, ret = 0;
+	pid_t pid = GetProcessId(main_process);
+
+	pids[0] = (DWORD)pid;
+	len = 1;
+
+	/*
+	 * Even if Process32First()/Process32Next() seem to traverse the
+	 * processes in topological order (i.e. parent processes before
+	 * child processes), there is nothing in the Win32 API documentation
+	 * suggesting that this is guaranteed.
+	 *
+	 * Therefore, run through them at least twice and stop when no more
+	 * process IDs were added to the list.
+	 */
+	for (;;) {
+		int orig_len = len;
+
+		memset(&entry, 0, sizeof(entry));
+		entry.dwSize = sizeof(entry);
+
+		if (!Process32First(snapshot, &entry))
+			break;
+
+		do {
+			for (i = len - 1; i >= 0; i--) {
+				if (pids[i] == entry.th32ProcessID)
+					break;
+				if (pids[i] == entry.th32ParentProcessID)
+					pids[len++] = entry.th32ProcessID;
+			}
+		} while (len < max_len && Process32Next(snapshot, &entry));
+
+		if (orig_len == len || len >= max_len)
+			break;
+	}
+
+	for (i = len - 1; i >= 0; i--) {
+		HANDLE process = pids[i] == pid ? main_process :
+			OpenProcess(PROCESS_TERMINATE, FALSE, pids[i]);
+
+		if (process) {
+			if (!TerminateProcess(process, exit_status << 8))
+				ret = -1;
+			CloseHandle(process);
+		}
+	}
+
+	return ret;
+}
+
+/**
+ * Determine whether a process runs in the same architecture as the current
+ * one. That test is required before we assume that GetProcAddress() returns
+ * a valid address *for the target process*.
+ */
+static inline int process_architecture_matches_current(HANDLE process)
+{
+	static BOOL current_is_wow = -1;
+	BOOL is_wow;
+
+	if (current_is_wow == -1 &&
+	    !IsWow64Process (GetCurrentProcess(), &current_is_wow))
+		current_is_wow = -2;
+	if (current_is_wow == -2)
+		return 0; /* could not determine current process' WoW-ness */
+	if (!IsWow64Process (process, &is_wow))
+		return 0; /* cannot determine */
+	return is_wow == current_is_wow;
+}
+
+/**
+ * Inject a thread into the given process that runs ExitProcess().
+ *
+ * Note: as kernel32.dll is loaded before any process, the other process and
+ * this process will have ExitProcess() at the same address.
+ *
+ * This function expects the process handle to have the access rights for
+ * CreateRemoteThread(): PROCESS_CREATE_THREAD, PROCESS_QUERY_INFORMATION,
+ * PROCESS_VM_OPERATION, PROCESS_VM_WRITE, and PROCESS_VM_READ.
+ *
+ * The idea comes from the Dr Dobb's article "A Safer Alternative to
+ * TerminateProcess()" by Andrew Tucker (July 1, 1999),
+ * http://www.drdobbs.com/a-safer-alternative-to-terminateprocess/184416547
+ *
+ * If this method fails, we fall back to running terminate_process_tree().
+ */
+static int exit_process(HANDLE process, int exit_code)
+{
+	DWORD code;
+
+	if (GetExitCodeProcess(process, &code) && code == STILL_ACTIVE) {
+		static int initialized;
+		static LPTHREAD_START_ROUTINE exit_process_address;
+		PVOID arg = (PVOID)(intptr_t)exit_code;
+		DWORD thread_id;
+		HANDLE thread = NULL;
+
+		if (!initialized) {
+			HINSTANCE kernel32 = GetModuleHandle("kernel32");
+			if (!kernel32)
+				die("BUG: cannot find kernel32");
+			exit_process_address = (LPTHREAD_START_ROUTINE)
+				GetProcAddress(kernel32, "ExitProcess");
+			initialized = 1;
+		}
+		if (!exit_process_address ||
+		    !process_architecture_matches_current(process))
+			return terminate_process_tree(process, exit_code);
+
+		thread = CreateRemoteThread(process, NULL, 0,
+					    exit_process_address,
+					    arg, 0, &thread_id);
+		if (thread) {
+			CloseHandle(thread);
+			/*
+			 * If the process survives for 10 seconds (a completely
+			 * arbitrary value picked from thin air), fall back to
+			 * killing the process tree via TerminateProcess().
+			 */
+			if (WaitForSingleObject(process, 10000) ==
+			    WAIT_OBJECT_0)
+				return 0;
+		}
+
+		return terminate_process_tree(process, exit_code);
+	}
+
+	return 0;
+}
+
+#endif