fix potential bug in building process tree on Win

lib/procinfo.cpp

@@ -100,6 +100,25 @@ void find_children(PROC_MAP& pm) {
         int parentid = i->second.parentid;
         PROC_MAP::iterator j = pm.find(parentid);
         if (j == pm.end()) continue;    // should never happen
+#ifdef _WIN32
+        // In Windows:
+        // 1) PIDs are reused, possibly quickly
+        // 2) if a process creates children and then exits,
+        //    the parentID of the children are not cleared,
+        //    so they may soon refer to an unrelated process.
+        //    (this is horrible design, BTW)
+        // This can cause problems:
+        // - when we abort a BOINC app we kill the process and its descendants
+        //   (based on parent ID).  These could be unrelated processes.
+        // - If a BOINC app gets a process ID that is the parentID of
+        //   orphan processes, its CPU time will be computed incorrectly.
+        // To fix this, don't create a parent/child link
+        // if the parent was created after the child.
+        //
+        if (j->second.create_time.QuadPart > i->second.create_time.QuadPart) {
+            continue;
+        }
+#endif
         j->second.children.push_back(i->first);
     }
 }

lib/procinfo.h

@@ -35,9 +35,11 @@ struct PROCINFO {
         // running at or below priority of BOINC apps
     char command[256];
     bool scanned;
-
     double page_fault_rate;        // derived by higher-level code
     std::vector<int> children;
+#ifdef _WIN32
+    LARGE_INTEGER create_time;
+#endif
 
     PROCINFO() {
       clear();

lib/procinfo_win.cpp

@@ -97,6 +97,7 @@ int get_procinfo_XP(PROC_MAP& pm) {
         p.user_time = ((double) pProcesses->UserTime.QuadPart)/1e7;
         p.kernel_time = ((double) pProcesses->KernelTime.QuadPart)/1e7;
         p.is_low_priority = (pProcesses->BasePriority <= 4);
+        p.create_time = pProcesses->CreateTime;
         WideCharToMultiByte(CP_ACP, 0,
             pProcesses->ProcessName.Buffer,
             pProcesses->ProcessName.Length,