Kill builds when we get EOF on the log FD

This closes a long-time bug that allowed builds to hang Nix
indefinitely (regardless of timeouts) simply by doing

  exec > /dev/null 2>&1; while true; do true; done

Now, on EOF, we just send SIGKILL to the child to make sure it's
really gone.

1 files changed, 6 insertions, 5 deletions

diff --git a/src/libutil/util.hh b/src/libutil/util.hh
index 67d2891688..d00f9c6457 100644
--- a/src/libutil/util.hh
+++ b/src/libutil/util.hh
@@ -192,17 +192,18 @@ typedef std::unique_ptr<DIR, DIRDeleter> AutoCloseDir;
 
 class Pid
 {
-    pid_t pid;
-    bool separatePG;
-    int killSignal;
+    pid_t pid = -1;
+    bool separatePG = false;
+    int killSignal = SIGKILL;
 public:
     Pid();
     Pid(pid_t pid);
     ~Pid();
     void operator =(pid_t pid);
     operator pid_t();
-    void kill(bool quiet = false);
-    int wait(bool block);
+    int kill(bool quiet = false);
+    int wait();
+
     void setSeparatePG(bool separatePG);
     void setKillSignal(int signal);
     pid_t release();