# No Double-Checked Locking
# Detects double-checked locking patterns
id: no-double-checked-locking
name: Double-Checked Locking Should Not Be Used
severity: error
category: reliability
defect_class: correctness
inline_tier: blocking
language: java

message: "Double-checked locking should not be used"

description: |
  Double-checked locking is not thread-safe in Java due to memory
  model issues (instruction reordering). Use static initialization
  or make the whole method synchronized.

  ✅ FIX: Use static holder pattern

  ```java
  private static class Holder {
      static final Resource INSTANCE = new Resource();
  }
  public static Resource getInstance() {
      return Holder.INSTANCE;  // GOOD - static init
  }
  ```

query: |
  (if_statement
    condition: (binary_expression
      left: (identifier) @FIELD
      operator: ("==")
      right: ("null"))
    consequence: (block
      (synchronized_statement
        body: (block
          (if_statement
            condition: (binary_expression
              left: (identifier) @FIELD2
              operator: ("==")
              right: ("null")))))))

metavars:
  - FIELD
  - FIELD2

post_filter: is_double_checked_locking

tags:
  - reliability
  - java
  - concurrency
  - cert

examples:
  bad: |
    if (instance == null) {  // BAD - double-checked locking
        synchronized (lock) {
            if (instance == null) {
                instance = new Instance();
            }
        }
    }

  good: |
    private static class InstanceHolder {
        static final Instance INSTANCE = new Instance();
    }
    public Instance getInstance() {
        return InstanceHolder.INSTANCE;  // GOOD
    }

has_fix: false