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To guarantee safety, programs must test the {{while}} loop condition after returning from the {{wait()}} method. Although {{wait()}} is intended to block indefinitely until a notification is received, it must still be encased within a loop to prevent the following vulnerabilities \[[Bloch 2001|AA. Bibliography#Bloch 01]\]: |
- thread in the middle—A middle — A third thread can acquire the lock on the shared object during the interval between a notification being sent and the receiving thread resuming execution. This third thread can change the state of the object, leaving it inconsistent. This is a time-of-check-to-time-of-use (TOCTOU) condition.
- malicious notification—A notification — A random or malicious notification can be received when the condition predicate is false. Such a notification would cancel the
wait(). - misdelivered notification—The notification — The order in which threads execute after receipt of a
notifyAll()signal is unspecified. Consequently, an unrelated thread could start executing and discover that its condition predicate is satisfied. Consequently, it could resume execution, although it was required to remain dormant. Wiki Markup spurious wake-ups—Certain-ups --- Certain JVM implementations are vulnerable to spurious wake-ups that result in waiting threads waking up even without a notification \[[API 2006|AA. Bibliography#API 06]\].
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<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="ba673899c7f58cd4-2c1673a7-4aec497a-878d9f1e-2b81d13046378cd1ba4ef4cd"><ac:plain-text-body><![CDATA[ | [[Bloch 2001 | AA. Bibliography#Bloch 01]] | Item 50: Never invoke wait outside a loop | ]]></ac:plain-text-body></ac:structured-macro> | |
<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="86060861d1ca42f5-df8ddd62-4aff4b67-9f969eef-79f7972b36da5584ce42a308"><ac:plain-text-body><![CDATA[ | [[Lea 2000 | AA. Bibliography#Lea 00]] | 3.2.2 Monitor Mechanics, 1.3.2 Liveness | ]]></ac:plain-text-body></ac:structured-macro> | |
<ac:structured-macro ac:name="unmigrated-wiki-markup" ac:schema-version="1" ac:macro-id="d46ebb129b0790e5-2387cff9-44024af8-abae90e9-7b4b82fd4b5ea6acfaf03cef"><ac:plain-text-body><![CDATA[ | [[Goetz 2006 | AA. Bibliography#Goetz 06]] | Section 14.2, Using Condition Queues | ]]></ac:plain-text-body></ac:structured-macro> |
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