From dcc37c236c66ba463bd61fec23d046485d8a412f Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <e.dolstra@tudelft.nl>
Date: Tue, 1 Feb 2005 12:36:25 +0000
Subject: * nix-store, nix-instantiate: added an option `--add-root' to  
 immediately add the result as a permanent GC root.  This is the only   way to
 prevent a race with the garbage collector.  For instance, the   old style

    ln -s $(nix-store -r $(nix-instantiate foo.nix)) \
      /nix/var/nix/gcroots/result

  has two time windows in which the garbage collector can interfere
  (by GC'ing the derivation and the output, respectively).  On the
  other hand,

    nix-store --add-root /nix/var/nix/gcroots/result -r \
      $(nix-instantiate --add-root /nix/var/nix/gcroots/drv \
        foo.nix)

  is safe.

* nix-build: use `--add-root' to prevent GC races.
---
 src/libmain/shared.cc | 24 +++++++++++++++++++++++-
 src/libmain/shared.hh |  4 ++++
 2 files changed, 27 insertions(+), 1 deletion(-)

(limited to 'src/libmain')

diff --git a/src/libmain/shared.cc b/src/libmain/shared.cc
index 23fcf28916be..5c994d7b47af 100644
--- a/src/libmain/shared.cc
+++ b/src/libmain/shared.cc
@@ -31,6 +31,28 @@ void sigintHandler(int signo)
 }
 
 
+Path makeRootName(const Path & gcRoot, int & counter)
+{
+    counter++;
+    if (counter == 1)
+        return gcRoot;
+    else
+        return (format("%1%-%2%") % gcRoot % counter).str();
+}
+
+
+void printGCWarning()
+{
+    static bool warned = false;
+    if (!warned) {
+        printMsg(lvlInfo,
+            "warning: you did not specify `--add-root'; "
+            "the result might be removed by the garbage collector");
+        warned = true;
+    }
+}
+
+
 void setLogType(string lt)
 {
     if (lt == "pretty") logType = ltPretty;
@@ -183,7 +205,7 @@ static void initAndRun(int argc, char * * argv)
 
     /* Automatically clean up the temporary roots file when we
        exit. */
-    RemoveTempRoots removeTempRoots;
+    RemoveTempRoots removeTempRoots; /* unused variable - don't remove */
 
     run(remaining);
 }
diff --git a/src/libmain/shared.hh b/src/libmain/shared.hh
index 76b639e3785d..82da7550626f 100644
--- a/src/libmain/shared.hh
+++ b/src/libmain/shared.hh
@@ -17,6 +17,10 @@ void run(Strings args);
 /* Should print a help message to stdout and return. */
 void printHelp();
 
+/* Ugh.  No better place to put this. */
+Path makeRootName(const Path & gcRoot, int & counter);
+void printGCWarning();
+
 
 extern string programId;
 
-- 
cgit 1.4.1