mingw: use real pid

The Windows port have so far been using process handles in place
of PID. However, this is not work consistent with what getpid
returns.

PIDs are system-global identifiers, but process handles are local
to a process. Using PIDs instead of process handles allows, for
instance, a user to kill a hung process with the Task Manager,
something that would have been impossible with process handles.

Change the code to use the real PID, and use OpenProcess to get a
process-handle. Store the PID and the process handle in a linked
list protected by a critical section, so we can safely close the
process handle later.

Linked list code written by Pat Thoyts.

Signed-off-by: Erik Faye-Lund <kusmabite@gmail.com>
Signed-off-by: Pat Thoyts <patthoyts@users.sourceforge.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

compat/mingw.c

@@ -702,6 +702,14 @@ static int env_compare(const void *a, const void *b)
 	return strcasecmp(*ea, *eb);
 }
 
+struct pinfo_t {
+	struct pinfo_t *next;
+	pid_t pid;
+	HANDLE proc;
+} pinfo_t;
+struct pinfo_t *pinfo = NULL;
+CRITICAL_SECTION pinfo_cs;
+
 static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **env,
 			      const char *dir,
 			      int prepend_cmd, int fhin, int fhout, int fherr)
@@ -794,7 +802,26 @@ static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **env,
 		return -1;
 	}
 	CloseHandle(pi.hThread);
-	return (pid_t)pi.hProcess;
+
+	/*
+	 * The process ID is the human-readable identifier of the process
+	 * that we want to present in log and error messages. The handle
+	 * is not useful for this purpose. But we cannot close it, either,
+	 * because it is not possible to turn a process ID into a process
+	 * handle after the process terminated.
+	 * Keep the handle in a list for waitpid.
+	 */
+	EnterCriticalSection(&pinfo_cs);
+	{
+		struct pinfo_t *info = xmalloc(sizeof(struct pinfo_t));
+		info->pid = pi.dwProcessId;
+		info->proc = pi.hProcess;
+		info->next = pinfo;
+		pinfo = info;
+	}
+	LeaveCriticalSection(&pinfo_cs);
+
+	return (pid_t)pi.dwProcessId;
 }
 
 static pid_t mingw_spawnve(const char *cmd, const char **argv, char **env,
@@ -1518,6 +1545,50 @@ char *getpass(const char *prompt)
 	return strbuf_detach(&buf, NULL);
 }
 
+pid_t waitpid(pid_t pid, int *status, unsigned options)
+{
+	HANDLE h = OpenProcess(SYNCHRONIZE | PROCESS_QUERY_INFORMATION,
+	    FALSE, pid);
+	if (!h) {
+		errno = ECHILD;
+		return -1;
+	}
+
+	if (options == 0) {
+		struct pinfo_t **ppinfo;
+		if (WaitForSingleObject(h, INFINITE) != WAIT_OBJECT_0) {
+			CloseHandle(h);
+			return 0;
+		}
+
+		if (status)
+			GetExitCodeProcess(h, (LPDWORD)status);
+
+		EnterCriticalSection(&pinfo_cs);
+
+		ppinfo = &pinfo;
+		while (*ppinfo) {
+			struct pinfo_t *info = *ppinfo;
+			if (info->pid == pid) {
+				CloseHandle(info->proc);
+				*ppinfo = info->next;
+				free(info);
+				break;
+			}
+			ppinfo = &info->next;
+		}
+
+		LeaveCriticalSection(&pinfo_cs);
+
+		CloseHandle(h);
+		return pid;
+	}
+	CloseHandle(h);
+
+	errno = EINVAL;
+	return -1;
+}
+
 #ifndef NO_MINGW_REPLACE_READDIR
 /* MinGW readdir implementation to avoid extra lstats for Git */
 struct mingw_DIR

compat/mingw.h

@@ -140,13 +140,7 @@ static inline int mingw_unlink(const char *pathname)
 }
 #define unlink mingw_unlink
 
-static inline pid_t waitpid(pid_t pid, int *status, unsigned options)
-{
-	if (options == 0)
-		return _cwait(status, pid, 0);
-	errno = EINVAL;
-	return -1;
-}
+pid_t waitpid(pid_t pid, int *status, unsigned options);
 
 #ifndef NO_OPENSSL
 #include <openssl/ssl.h>
@@ -321,11 +315,13 @@ void free_environ(char **env);
 static int mingw_main(); \
 int main(int argc, const char **argv) \
 { \
+	extern CRITICAL_SECTION pinfo_cs; \
 	_fmode = _O_BINARY; \
 	_setmode(_fileno(stdin), _O_BINARY); \
 	_setmode(_fileno(stdout), _O_BINARY); \
 	_setmode(_fileno(stderr), _O_BINARY); \
 	argv[0] = xstrdup(_pgmptr); \
+	InitializeCriticalSection(&pinfo_cs); \
 	return mingw_main(argc, argv); \
 } \
 static int mingw_main(c,v)