lidavidm commented on code in PR #37498:
URL: https://github.com/apache/arrow/pull/37498#discussion_r1321595468
##########
docs/source/java/memory.rst:
##########
@@ -288,6 +288,54 @@ Finally, enabling the ``TRACE`` logging level will
automatically provide this st
| at RootAllocator.close (RootAllocator.java:29)
| at (#8:1)
+Sometimes, explicitly passing allocators around is difficult. For example, it
+can be hard to pass around extra state, like an allocator, through layers of
+existing application or framework code. A global or singleton allocator
instance
+can be useful here, though it should not be your first choice.
+
+How this works:
+
+1. Set up a global allocator in a singleton class.
+2. Provide methods to create child allocators from the global allocator.
+3. Give child allocators proper names to make it easier to figure out where
+ allocations occurred in case of errors.
+4. Ensure that resources are properly closed.
+5. Check that the global allocator is empty at some suitable point, such as
+ right before program shutdown.
+6. If it is not empty, review the above allocation bugs.
+
+.. code-block:: java
+
+ //1
+ private static final BufferAllocator allocator = new RootAllocator();
+ private static final AtomicInteger childNumber = new AtomicInteger(0);
+ ...
+ //2
+ public static BufferAllocator getChildAllocator() {
+ return allocator.newChildAllocator(nextChildName(), 0, Long.MAX_VALUE);
+ }
+ ...
+ //3
+ private static String nextChildName() {
+ return "Allocator-Child-" + childNumber.incrementAndGet();
+ }
+ ...
+ //4: Business code
+ try (BufferAllocator allocator = GlobalAllocator.getChildAllocator()) {
+ ...
+ }
+ ...
+ //5
+ public static void checkGlobalCleanUpResources() {
+ ...
+ if (!allocator.getChildAllocators().isEmpty()) {
+ throw new IllegalStateException(...)
+ ));
+ } else if (allocator.getAllocatedMemory() != 0) {
+ throw new IllegalStateException(...);
+ }
+ }
Review Comment:
```suggestion
public static void checkGlobalCleanUpResources() {
...
if (!allocator.getChildAllocators().isEmpty()) {
throw new IllegalStateException(...);
} else if (allocator.getAllocatedMemory() != 0) {
throw new IllegalStateException(...);
}
}
```
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