libutil: make AutoCloseFD a better resource

add a reset() method to close the wrapped fd instead of assigning magic
constants. also make the from-fd constructor explicit so you can't
accidentally assign the *wrong* magic constant, or even an unrelated
integer that also just happens to be an fd by pure chance.

Change-Id: I51311b0f6e040240886b5103d39d1794a6acc325

1 files changed, 3 insertions, 3 deletions

diff --git a/src/libstore/build/hook-instance.cc b/src/libstore/build/hook-instance.cc
index 337c60bd4..ea4c2e508 100644
--- a/src/libstore/build/hook-instance.cc
+++ b/src/libstore/build/hook-instance.cc
@@ -61,8 +61,8 @@ HookInstance::HookInstance()
     });
 
     pid.setSeparatePG(true);
-    fromHook.writeSide = -1;
-    toHook.readSide = -1;
+    fromHook.writeSide.reset();
+    toHook.readSide.reset();
 
     sink = FdSink(toHook.writeSide.get());
     std::map<std::string, Config::SettingInfo> settings;
@@ -76,7 +76,7 @@ HookInstance::HookInstance()
 HookInstance::~HookInstance()
 {
     try {
-        toHook.writeSide = -1;
+        toHook.writeSide.reset();
         if (pid != -1) pid.kill();
     } catch (...) {
         ignoreException();