lib: Evaluate {QemuNBD,Nbdkit}.is_installed only once

Using a lazy suspension we can make sure these are evaluated only once per run.
libguestfs · Nov 23, 2021 · f34865c · f34865c
1 parent ab55f94
commit f34865c
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Showing 2 changed files with 6 additions and 4 deletions.
diff --git a/lib/nbdkit.ml b/lib/nbdkit.ml
@@ -26,8 +26,9 @@ open Unix_utils
 
 open Utils
 
-let is_installed () =
-  Sys.command "nbdkit --version >/dev/null 2>&1" = 0
+let is_installed =
+  let test = lazy (Sys.command "nbdkit --version >/dev/null 2>&1" = 0) in
+  fun () -> Lazy.force test
 
 type config = (string * string) list
 

diff --git a/lib/qemuNBD.ml b/lib/qemuNBD.ml
@@ -28,8 +28,9 @@ open Unix_utils
 
 open Utils
 
-let is_installed () =
-  Sys.command "qemu-nbd --version >/dev/null 2>&1" = 0
+let is_installed =
+  let test = lazy (Sys.command "qemu-nbd --version >/dev/null 2>&1" = 0) in
+  fun () -> Lazy.force test
 
 type version = int * int * int