11/5/2022 0 Comments Java stackThe reserved zone during the execution of a critical method, JVM unprotects Reserved zone acts like a yellow zone with one exception: when stack banging hits The idea is to reserve an additional stack page for execution of such critical methods. The problem and the solution is described in JEP 270. In an inconsistent state, so no other thread would be able to acquire the lock again. In the middle of lock() or unlock() method, the ReentrantLock object may remain Has been added in JDK 9 to address the problem when StackOverflowError occurs To provide some stack space for writing hs_err_pid.log. Should never be touched, but if this happens for any reason, JVM treats thisĪs a fatal error and dies leaving the final crash report. The yellow pages are reguarded later during stack unwinding. the pages are unprotected) to give some extra stack space for the exception SIGSEGV happens, and the signal handler resumes the current thread from the continuation If a stack banging instruction hits the yellow zone, the signal handler detects which guard page has been accessed, and acts accordingly. However, these SIGSEGVs are managed by the JVM, All the guard pages are initiallyįrom both reading and writing, so that any access to these pages causes On the top of the stack – the guard zone. When JVM allocates a stack for a new thread, it reserves a few pages Otherwise it touches one of the guard pages,Īnd the hardware exception is triggered. JAVA STACK FREEIf there is enough free space above the current frame, It writes any meaningless value from EAX register onto the stack somewhere above See TemplateInterpreterGenerator::generate_stack_overflow_check. To the stack pointer in RSP register adjusted by the size of the current stack frame, It takes the address of a stack limit for the current thread and compares it Interpreter performs a straightforward check in a method prologue. There are some interesting details though. It simply performs a stack overflow check on every method invocation. But how does JVM know when it’s time to throw an error? Java obviously throws StackOverflowError. When a call chain becomes too deep and there is no free space on the stack to create more frames, This is usually enough to place several thousand average frames. The stack size is configured with -Xss option and defaults to 1 MB on a 64-bit system. This seems intuitive, since the optimizing compiler does not need to haveĪll the local variables and all the monitors on the stack. The compiled frame is often smaller than the interpreter frame for the same method – The maximum stack usage of any Java method is known beforehand,īut may vary depending on whether the method is interpreted or compiled. Unlike C, where stack space can be allocated dynamically with Java methods and native methods share the same stack with Java and native frames HotSpot JVM uses one contiguous stack for all the above purposes. The classical “C” stack required for native method execution. Which holds operands for bytecode instructions. Indeed had chunked stacks allocated in Java heap. Java ME virtual machine (that I worked on at Sun Microsystems) Which stores local variables and keeps track of method invocations.Īs the specification says, this stack does not need to be contiguousĪnd may be heap allocated. That in Java there are at least 3 different notions of a stack: Here is an example of an EmptyStackException thrown when an element is attempted to be popped from an empty stack: import you probably know, HotSpot JVM has one-to-one mapping of Java threads to OS threads.Įach thread is associated with its own stack. For example, if the Stack.pop() method is used to remove an object at the top of an empty stack, an EmptyStackException is thrown. The EmptyStackException is thrown when attempting to access elements in an empty stack in Java. Since the EmptyStackException is an unchecked exception, it does not need to be declared in the throws clause of a method or constructor. The EmptyStackException is a runtime exception in Java that is thrown by methods in the Stack class to indicate that the stack is empty.
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