org.sqlite.database.sqlite

Class CloseGuard

java.lang.Object

org.sqlite.database.sqlite.CloseGuard

public final class CloseGuard
extends java.lang.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 {
               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 {
               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.

Note that the null check on guard in the finalizer is to cover cases where a constructor throws an exception causing the guard to be uninitialized.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static interface	CloseGuard.Reporter Interface to allow customization of reporting behavior.

Method Summary

Modifier and Type	Method and Description
void	close() Marks this CloseGuard instance as closed to avoid warnings on finalization.
static CloseGuard	get() Returns a CloseGuard instance.
static CloseGuard.Reporter	getReporter() Returns non-null CloseGuard.Reporter.
void	open(java.lang.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.
static void	setEnabled(boolean enabled) Used to enable or disable CloseGuard.
static void	setReporter(CloseGuard.Reporter reporter) Used to replace default Reporter used to warn of CloseGuard violations.
void	warnIfOpen() If CloseGuard is enabled, logs a warning if the caller did not properly cleanup by calling an explicit close method before finalization.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

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(java.lang.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:

java.lang.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.