BOOT_WATCHERS_DISABLE - creates a --disable-watchers long-only flag and a (#564)

BOOT_WATCHERS_DISABLE env variable and property.  Kills the directory
recursion for adding watches based on the flag.

Author: gtrak

boot/core/src/boot/main.clj

@@ -32,6 +32,7 @@
                  (update-in %1 [%2] (fnil assoc {}) (keyword k) v))]
    ["-i" "--init EXPR"           "Evaluate EXPR in the boot.user context."
     :assoc-fn #(update-in %1 [%2] (fnil conj []) (read-string %3))]
+   [nil  "--disable-watchers"    "Disable registering file watches (inotify/FSEvents) for constrained environments."]
    ["-f" "--file PATH"           "Evaluate PATH (implies -BP). Args and options passed to -main."]
    ["-h" "--help"                "Print basic usage and help info."]
    ["-o" "--offline"             "Don't attempt to access remote repositories." :id :offline?]
@@ -144,7 +145,10 @@
         boot?             (and boot? (not (:file opts)))
         verbosity         (if (:quiet opts)
                             (* -1 @util/*verbosity*)
-                            (or (:verbose opts) 0))]
+                            (or (:verbose opts) 0))
+        watchers?          (if (:disable-watchers opts)
+                             false
+                             @util/*watchers?*)]
 
     (when (seq errs)
       (util/exit-error
@@ -155,9 +159,12 @@
 
     (swap! util/*verbosity* + verbosity)
 
+    (reset! util/*watchers?* watchers?)
+
     (pod/with-eval-in worker-pod
       (require '[boot.util :as util])
-      (swap! util/*verbosity* + ~verbosity))
+      (swap! util/*verbosity* + ~verbosity)
+      (reset! util/*watchers?* ~watchers?))
 
     (binding [*out*               (util/auto-flush *out*)
               *err*               (util/auto-flush *err*)

boot/core/src/boot/task/built_in.clj

@@ -45,6 +45,7 @@
                  ["" "BOOT_FILE"                 "Build script name (build.boot)."]
                  ["" "BOOT_GPG_COMMAND"          "System gpg command (gpg)."]
                  ["" "BOOT_HOME"                 "Directory where boot stores global state (~/.boot)."]
+                 ["" "BOOT_WATCHERS_DISABLE"      "Set to 'yes' to turn off inotify/FSEvents watches."]
                  ["" "BOOT_JAVA_COMMAND"         "Specify the Java executable (java)."]
                  ["" "BOOT_JVM_OPTIONS"          "Specify JVM options (Unix/Linux/OSX only)."]
                  ["" "BOOT_LOCAL_REPO"           "The local Maven repo path (~/.m2/repository)."]

boot/pod/src/boot/util.clj

@@ -17,6 +17,20 @@
 
 (declare print-ex)
 
+(defn watchers?-system-default
+  "Return whether we should register file watches on this
+  system. Constrained environments like clould build containers limit
+  the number of inotify handles, and watchers are only necessary for
+  interactive dev, not one-shot jobs.  environment variable or
+  configuration option BOOT_WATCHERS_DISABLE to either '1' or 'yes' to
+  disable inotify; any other value keeps normal behavior."
+  []
+  (let [value (boot.App/config "BOOT_WATCHERS_DISABLE")]
+    (if (string/blank? value)
+      true
+      (not (#{"1" "yes"}
+            (string/lower-case value))))))
+
 (defn colorize?-system-default
   "Return whether we should colorize output on this system. The default
   console on Windows does not interprete ANSI escape codes, so colorized
@@ -50,6 +64,10 @@
   will be printed with boot output."
   (atom (colorize?-system-default)))
 
+(def ^:dynamic *watchers?*
+  "Atom containing the value that determines whether inotify watches are registered"
+  (atom (watchers?-system-default)))
+
 (defn- print*
   [verbosity color args]
   (when (>= @*verbosity* verbosity)

boot/worker/src/boot/watcher.clj

@@ -58,11 +58,12 @@
 
 (defn- register-recursive
   [service path events]
-  (util/dbug* "registering %s %s\n" path events)
-  (register service path events)
-  (doseq [dir (.listFiles (io/file path))]
-    (when (.isDirectory dir)
-      (register-recursive service dir events))))
+  (when @util/*watchers?*
+    (util/dbug* "registering %s %s\n" path events)
+    (register service path events)
+    (doseq [dir (.listFiles (io/file path))]
+      (when (.isDirectory dir)
+        (register-recursive service dir events)))))
 
 (defn- new-watch-service []
   (if (= "Mac OS X" (System/getProperty "os.name"))