win32: improvements to implementation of kill(2)

Extend the implementation of kill(2) so that:

- Sending the TERM signal asks the target process to exit.  As on
  Unix it may not comply.

- Sending the KILL signal forcibly terminates the target process.

- Using a negative pid treats the target process as a process
  group leader and signals it and all of its descendants.

- Using a pid of zero treats the current process as a process
  group leader and signals it and all of its descendants.

Signed-off-by: Ron Yorston <rmy@pobox.com>

1 files changed, 94 insertions, 87 deletions

diff --git a/win32/process.c b/win32/process.c
index 7840741c4..ada0d743f 100644
--- a/win32/process.c
+++ b/win32/process.c
@@ -412,23 +412,25 @@ UNUSED_PARAM
         return sp;
 }
 
-/*
- * 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).
+/**
+ * If the process ID is positive invoke the callback for that process
+ * only.  If negative or zero invoke the callback for all descendants
+ * of the indicated process.  Zero indicates the current process; negative
+ * indicates the process with process ID -pid.
  */
-static int terminate_process_tree(HANDLE main_process, int exit_status)
+typedef int (*kill_callback)(pid_t pid, int exit_code);
+
+static int kill_pids(pid_t pid, int exit_code, kill_callback killer)
 {
-        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;
+        if(pid > 0)
+                pids[0] = (DWORD)pid;
+        else if (pid == 0)
+                pids[0] = (DWORD)getpid();
+        else
+                pids[0] = (DWORD)-pid;
         len = 1;
 
         /*
@@ -440,40 +442,46 @@ static int terminate_process_tree(HANDLE main_process, int exit_status)
          * Therefore, run through them at least twice and stop when no more
          * process IDs were added to the list.
          */
-        for (;;) {
-                int orig_len = len;
+        if (pid <= 0) {
+                HANDLE snapshot = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0);
 
-                memset(&entry, 0, sizeof(entry));
-                entry.dwSize = sizeof(entry);
+                if (snapshot == INVALID_HANDLE_VALUE) {
+                        errno = err_win_to_posix(GetLastError());
+                        return -1;
+                }
 
-                if (!Process32First(snapshot, &entry))
-                        break;
+                for (;;) {
+                        PROCESSENTRY32 entry;
+                        int orig_len = len;
 
-                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));
+                        memset(&entry, 0, sizeof(entry));
+                        entry.dwSize = sizeof(entry);
 
-                if (orig_len == len || len >= max_len)
-                        break;
-        }
+                        if (!Process32First(snapshot, &entry))
+                                break;
 
-        for (i = len - 1; i > 0; i--) {
-                HANDLE process = OpenProcess(PROCESS_TERMINATE, FALSE, pids[i]);
+                        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 (process) {
-                        if (!TerminateProcess(process, exit_status))
-                                ret = -1;
-                        CloseHandle(process);
+                        if (orig_len == len || len >= max_len)
+                                break;
+                }
+
+                CloseHandle(snapshot);
+        }
+
+        for (i = len - 1; i >= 0; i--) {
+                if (killer(pids[i], exit_code)) {
+                        errno = err_win_to_posix(GetLastError());
+                        ret = -1;
                 }
         }
-        if (!TerminateProcess(main_process, exit_status))
-                ret = -1;
-        CloseHandle(main_process);
 
         return ret;
 }
@@ -499,96 +507,95 @@ static inline int process_architecture_matches_current(HANDLE process)
 }
 
 /**
- * This function tries 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.
+ * This function tries to terminate a Win32 process, as gently as possible,
+ * by injecting a thread that calls 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)
+static int exit_process(pid_t pid, int exit_code)
 {
+        HANDLE process;
         DWORD code;
+        int ret = 0;
+
+        if (!(process = OpenProcess(SYNCHRONIZE | PROCESS_CREATE_THREAD |
+                        PROCESS_QUERY_INFORMATION |
+                        PROCESS_VM_OPERATION | PROCESS_VM_WRITE |
+                        PROCESS_VM_READ, FALSE, pid))) {
+                return -1;
+        }
 
         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;
+                HANDLE thread;
 
                 if (!initialized) {
                         HINSTANCE kernel32 = GetModuleHandle("kernel32");
                         if (!kernel32) {
                                 fprintf(stderr, "BUG: cannot find kernel32");
-                                return -1;
+                                ret = -1;
+                                goto finish;
                         }
                         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);
+                    !process_architecture_matches_current(process)) {
+                        ret = -1;
+                        goto finish;
+                }
 
-                thread = CreateRemoteThread(process, NULL, 0,
+                if ((thread = CreateRemoteThread(process, NULL, 0,
                                             exit_process_address,
-                                            arg, 0, &thread_id);
-                if (thread) {
-                        DWORD result;
-
+                                            arg, 0, &thread_id))) {
                         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().
-                         */
-                        result = WaitForSingleObject(process, 10000);
-                        if (result == WAIT_OBJECT_0) {
-                                CloseHandle(process);
-                                return 0;
-                        }
                 }
-
-                return terminate_process_tree(process, exit_code);
         }
 
-        return 0;
+ finish:
+        CloseHandle(process);
+        return ret;
 }
 
-int kill(pid_t pid, int sig)
+/*
+ * This way of terminating processes is not gentle: they get no chance to
+ * clean up after themselves (closing file handles, removing .lock files,
+ * terminating spawned processes (if any), etc).
+ */
+static int terminate_process(pid_t pid, int exit_code)
 {
-        HANDLE h;
-
-        if (pid > 0 && sig == SIGTERM) {
-                if ((h = OpenProcess(SYNCHRONIZE | PROCESS_CREATE_THREAD |
-                                PROCESS_QUERY_INFORMATION |
-                                PROCESS_VM_OPERATION | PROCESS_VM_WRITE |
-                                PROCESS_VM_READ, FALSE, pid)))
-                        return exit_process(h, 128 + sig);
-                if ((h=OpenProcess(PROCESS_TERMINATE, FALSE, pid)) != NULL &&
-                                terminate_process_tree(h, 128 + sig)) {
-                        CloseHandle(h);
-                        return 0;
-                }
+        HANDLE process;
+        int ret;
 
-                errno = err_win_to_posix(GetLastError());
-                if (h != NULL)
-                        CloseHandle(h);
+        if (!(process=OpenProcess(PROCESS_TERMINATE, FALSE, pid))) {
                 return -1;
         }
 
+        ret = !TerminateProcess(process, exit_code);
+        CloseHandle(process);
+
+        return ret;
+}
+
+int kill(pid_t pid, int sig)
+{
+        if (sig == SIGTERM) {
+                return kill_pids(pid, 128+sig, exit_process);
+        }
+        else if (sig == SIGKILL) {
+                return kill_pids(pid, 128+sig, terminate_process);
+        }
+
         errno = EINVAL;
         return -1;
 }