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Passing same buffer as two method arguments does not read back modified content

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还没有人认领这个 Issue。

评估

难度
4/5
预计耗时
3-5 天
新手友好度
35/100
Issue 类型
缺陷
描述清晰度
基本清楚
活跃度
停滞
技术栈
java
领域
tooling

调研方向

从 JNA 针对入口点 do_something(ByteBuffer out, ByteBuffer in) 的调用路径以及堆支持的 ByteBuffer 参数处理开始。在 JNA 5.5.0 上使用同一个缓冲区作为两个参数来重现该调用，然后验证 native 函数返回后修改后的输出仍然可见。

由索引模型根据 Issue 内容生成。

描述

feature request

Assume the following native library function, which reads from in and writes to out:

int do_something(void *out, void *in);

mapped to the following interface in Jave:

public interface mylibrary extends Library {
	public int do_something(ByteBuffer out, ByteBuffer in);
}

When calling this function with the same buffer backed by a heap-allocated array as both output and input argument, i.e.:

public void process(ByteBuf buffer) {
    // buffer is backed by heap-allocated array
    mylibraryInstance.do_something(buffer, buffer);
}

then the buffer will not be updated to reflect the content that was written to out within the native function implementation.

I assume this is because each argument will be processed individually, the buffer will be copied two times into native memory, both instances will be read back after the function call and the second argument (in, unmodified) replaces the first argument (out, modified & expected content).

Workaround: Create a new buffer before calling the native function (and write it back afterwards):

public void process(ByteBuf buffer) {
    ByteBuffer outputBuffer = ByteBuffer.allocate(buffer.remaining());
    outputBuffer.limit(buffer.remaining());
    mylibraryInstance.do_something(outputBuffer, buffer);
    // here, outputBuffer has the expected (modified) content - write back to original buffer
}

Version of JNA and related jars: jna 5.5.0 and jna-platform 5.5.0
Version and vendor of the java virtual machine: Oracle JDK 12.0.2

主要语言
Java
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