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Quest For "Unbreakable Java" Unites ABAP & Java
jg21 writes "Writing an article about "A Java Server That Never Goes Down" is pure hubris, but a German developer who says he's been "eating, sleeping, and drinking Java" for 8 years doesn't seem to care and his article brings to light the aspects of VM we rarely think of as he introduces "user isolation" and tells about some interesting work SAP in Germany is doing in that area, merging the Java and the ABAP worlds."
It seems I have been sleeping under some rock! For this is the first time I am hearing of ABAP.
Unbreakable Java: A Java Server That Never Goes Down
December 31, 2004
Summary
Developers using Java on clients or in small projects may not believe that there is a fundamental problem with Java's robustness. People working with huge applications and application servers written in Java know about the problem but may doubt that it's possible to build something like an unbreakable Java architecture.
By Thomas Smits
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Developers using Java on clients or in small projects may not believe that there is a fundamental problem with Java's robustness. People working with huge applications and application servers written in Java know about the problem but may doubt that it's possible to build something like an unbreakable Java architecture. Some may even remember the White Star Line promising that their ocean liner Titanic was unsinkable; an iceberg in the North Atlantic proved them wrong and demonstrated that there is no such thing as an unsinkable ship. Is it really possible to build a Java application server that never goes down?
It's All About Isolation
The key to understanding robust Java is isolation, isolation, and isolation. Robust applications, especially robust application servers, require a high level of isolation between users. It's not acceptable that an error occurring while processing one user's request may affect all users connected to the system. The complexity of software systems makes it impossible to develop software that is completely free of errors, so errors will always happen. Only isolation can provide real robustness by limiting the impact of errors.
The design of the Java Virtual Machine ignores the painful lessons operating system vendors have learned in the past 40 years. The concepts of processes, virtual memory management, and different protection modes for kernel and user code can be found in all modern operating systems. They focus on the question of isolation and therefore robustness: an application with errors cannot affect the other applications running in the system.
In contrast, Java follows the all-in-one-VM paradigm: everything is processed inside one virtual machine running in one operating system process. Inside the VM, parallelism is implemented using threads with no separation regarding memory or other resources. In this respect Java has not changed since its invention in the early nineties. The fact that Java was originally invented as a programming language for embedded devices may explain this approach.
There Is No Isolation in Java
Java does not have a problem with isolation; there is virtually no isolation at all. Java tries to avoid dangerous concepts like manual memory management (this is like taking some of the icebergs out of the ocean) and it can't be denied that it provides at least some isolation concepts, but a Java Virtual Machine is still easy to break. For example, class loaders make it possible to partition an application into parts that cannot see and access each other directly, which provides some isolation. Going back to our nautical example from the very beginning, this is exactly what was supposed to make the Titanic unsinkable: the ship consisted of separate compartments and water pouring into the ship was supposed to be stopped by the bulkheads separating the compartments - unfortunately the iceberg was too big and way too many compartments filled up with water. In terms less familiar to the sailor but more familiar to the developer: all the fancy isolation built with class loaders does not help if you have memory leaks, threads running amok, or even bugs in the VM.
SAP's Approach to Isolation
SAP's ABAP application server - the powerhouse underlying enterprise-scale R/3 business solutions - was based on the concept of process isolation from the very beginning. It consists of a dispatcher and a bunch of work processes handling the requests. The work processes are normal operating system (OS) processes and the OS provides a high level of isolation for free.
Wow, a post bashing Java on Slashdot. How incredibly original and refreshing!
Well, at least you are honest about your bias.
Being bitter is drinking poison and hoping someone else will die