Package dalvik.system

Class CloseGuard

  • public final class CloseGuard
extends Object
    CloseGuard is a mechanism for flagging implicit finalizer cleanup of resources that should have been cleaned up by explicit close methods (aka "explicit termination methods" in Effective Java).

    A simple example: 

       
   class Foo {

       private final CloseGuard guard = CloseGuard.get();

       ...

       public Foo() {
           ...;
           guard.open("cleanup");
       }

       public void cleanup() {
          guard.close();
          ...;
       }

       protected void finalize() throws Throwable {
           try {
               // Note that guard could be null if the constructor threw.
               if (guard != null) {
                   guard.warnIfOpen();
               }
               cleanup();
           } finally {
               super.finalize();
           }
       }
   }
    In usage where the resource to be explicitly cleaned up are allocated after object construction, CloseGuard protection can be deferred. For example: 
       
   class Bar {

       private final CloseGuard guard = CloseGuard.get();

       ...

       public Bar() {
           ...;
       }

       public void connect() {
          ...;
          guard.open("cleanup");
       }

       public void cleanup() {
          guard.close();
          ...;
       }

       protected void finalize() throws Throwable {
           try {
               // Note that guard could be null if the constructor threw.
               if (guard != null) {
                   guard.warnIfOpen();
               }
               cleanup();
           } finally {
               super.finalize();
           }
       }
   }
    When used in a constructor calls to open should occur at the end of the constructor since an exception that would cause abrupt termination of the constructor will mean that the user will not have a reference to the object to cleanup explicitly. When used in a method, the call to open should occur just after resource acquisition.

    • Method Detail

      • get

        public static CloseGuard get()
        Returns a CloseGuard instance. If CloseGuard is enabled, #open(String) can be used to set up the instance to warn on failure to close. If CloseGuard is disabled, a non-null no-op instance is returned.

      • setEnabled

        public static void setEnabled​(boolean enabled)
        Used to enable or disable CloseGuard. Note that CloseGuard only warns if it is enabled for both allocation and finalization.

      • setReporter

        public static void setReporter​(CloseGuard.Reporter reporter)
        Used to replace default Reporter used to warn of CloseGuard violations. Must be non-null.

      • getReporter

        public static CloseGuard.Reporter getReporter()
        Returns non-null CloseGuard.Reporter.

      • open

        public void open​(String closer)
        If CloseGuard is enabled, open initializes the instance with a warning that the caller should have explicitly called the closer method instead of relying on finalization.
        Parameters:
        closer - non-null name of explicit termination method
        Throws:
        NullPointerException - if closer is null, regardless of whether or not CloseGuard is enabled

      • close

        public void close()
        Marks this CloseGuard instance as closed to avoid warnings on finalization.

      • warnIfOpen

        public void warnIfOpen()
        If CloseGuard is enabled, logs a warning if the caller did not properly cleanup by calling an explicit close method before finalization. If CloseGuard is disabled, no action is performed.