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One of the most promising approaches to Java acceleration in embedded systems is a bytecode-to-C ahead-of-time compiler (AOTC). It improves the performance of a Java virtual machine (JVM) by translating bytecode into C code, which is then compiled into machine code via an existing C compiler. One important design issue in AOTC is efficient exception handling. Since the excepting point and the exception handler may locate in different methods on a call stack, control transfer between them should be streamlined, while an exception would be an ''exceptional'' event, so it should not slow down normal execution paths. Previous AOTCs often employed a technique called stack cutting based on a setjmp()/longjmp() pair, which we found is involved with too much performance overheads. Also, when the AOTC and the interpreter are employed concurrently (e.g., some methods are AOTCed while other methods are interpreted), the performance of normal execution paths is affected more seriously. This paper proposes a simpler solution based on an exception check after each method call, merged with garbage collection check for reducing its overhead. Our evaluation results on SPECjvm98 on Sun's CVM indicate that our technique can improve the performance of stack cutting by more than 25%. A similar performance benefit can be noted on a hybrid execution environment of both the AOTC and the interpreter.

The performance of embedded Java virtual machine can be improved by ahead-of-time compiler (AOTC), which translates bytecode into machine code in the server and installs the machine code on the client device. Although AOTC is more advantageous than just-in-time compiler (JITC) due to its absence of the translation overhead, AOTC cannot be applicable to dynamically downloaded classes at runtime. This paper proposes client-AOTC (c-AOTC) which performs AOTC on the client device using the JITC module installed on the device, complementing the server-AOTC. The machine code of a method translated by JITC is cached on a persistent memory of the device, and when the method is invoked again in a later run of the program, the machine code is loaded and executed directly without the translation and interpretation overhead. One of major issues in c-AOTC is relocation because some of the addresses used by the cached machine code are not correct when the machine code is loaded and used in a different run; those addresses should be corrected before they are used. Constant pool resolution and inlining complicate the relocation problem and we propose our solutions. We developed a c-AOTC on Sun's CDC VM reference implementation (RI) and our evaluation results indicate that c-AOTC can improve the performance significantly, as much as an average of 12%. We also experiment with the issue of reducing the number of c-AOTC methods to be cached when the persistent space is tight, with a graceful degradation of performance.

A Java bytecode-to-C ahead-of-time compiler (AOTC) can improve the performance of a Java virtual machine (JVM) by translating bytecode into C code, which is then compiled into machine code via an existing C compiler. Although AOTC is effective in embedded Java systems, a bytecode-to-C AOTC could not easily employ precise garbage collection (GC) due to a difficulty in making a GC map, which keeps information on where each root live object is located when GC occurs. This is one of the reasons why all previous JVMs using a bytecode-to-C AOTC employed conservative GC, which can lead to poorer GC performance with more frequent memory shortage, especially in embedded systems where memory is tight.In this paper, we propose a way of allowing precise GC in a bytecode-to-C AOTC by generating additional C code which collects GC map-equivalent information at runtime. In order to reduce this runtime overhead, we also propose two optimization techniques which remove unnecessary C code. Our experimental results on Sun's CVM indicate that we can support precise GC for bytecode-to-C AOTC with a relatively low overhead.

One of the most promising approaches to Java acceleration in embedded systems is a bytecode-to-C ahead-of-time compiler (AOTC). It improves the performance of a Java virtual machine (JVM) by translating bytecode into C code, which is then compiled into machine code via an existing C compiler. One important design issue in AOTC is efficient exception handling. Since the excepting point and the exception handler may locate in different methods on a call stack, control transfer between them should be streamlined, while an exception would be an "exceptional" event, so it should not slow down normal execution paths. Previous AOTCs often employed stack cutting based on a setjmp()/longjmp(), which we found is involved with too much overheads. This paper proposes a simpler solution based on an exception check after each method call, merged with garbage collection check for reducing its overhead. Our evaluation results on SPECjvm98 on Sun's CVM indicate that our technique can improve the performance of stack cutting by more than 25%.