C ++和Java进程之间的共享内存 [英] Shared memory between C++ and Java processes

问题描述

我的目标是将数据从C ++进程传递到Java进程，然后将结果接收回来.

My aim is to pass data from a C++ process to a Java process and then to receive a result back.

我已经通过命名管道实现了这一点，但是我希望共享数据而不是传递或复制数据，前提是访问会更快.

I have achieved this via a named pipe but I would prefer to share the data rather than passing or copying it, assuming the access would be faster.

最初，我想过要创建一个可以用Java读写的C ++共享段，但是我不确定是否可以通过JNI做到这一点，更不用说安全了.

Initially, I thought of creating a shared segment in C++ that I could write to and read with Java, but I'm not sure if this is possible via JNI, let alone safe.

我相信在Java中可以使用ByteBuffer.allocateDirect分配内存，然后使用GetDirectBufferAddress来访问C ++中的地址，但是如果我正确的话，这是针对JNI中的本机调用，而我无法在该地址中获取该地址.我的C ++程序?

I believe it's possible in Java to allocate the memory using ByteBuffer.allocateDirect and then use GetDirectBufferAddress to access the address in C++, but if I'm correct this is for native calls within JNI and I can't get this address in my C++ process?

迷失了.

非常感谢.

推荐答案

如果您拥有共享内存，例如使用 CreateFileMapping (Windows)或shmget(Unix)，您所需要的只是Java方面的本机方法.然后，您可以创建 ByteBuffer 直接使用 NewDirectByteBuffer 像这样:

If you have shared memory, for example using CreateFileMapping (Windows) or shmget (Unix), all you need is a native method on the Java side. Then you can create a ByteBuffer that directly accesses the shared memory using NewDirectByteBuffer like this:

JNIEXPORT jobject JNICALL Java_getSharedBuffer(JNIEnv* env, jobject caller) {
    void* myBuffer;
    int bufferLength;

现在，您必须获得一个指向共享内存的指针.在Windows上，您将使用以下内容:

Now you have to get a pointer to the shared memory. On Windows you would use something like this:

    bufferLength = 1024; // assuming your buffer is 1024 bytes big
    HANDLE mem = OpenFileMapping(FILE_MAP_READ, // assuming you only want to read
           false, "MyBuffer"); // assuming your file mapping is called "MyBuffer"
    myBuffer = MapViewOfFile(mem, FILE_MAP_READ, 0, 0, 0);
    // don't forget to do UnmapViewOfFile when you're finished

现在，您只需创建一个由该共享内存支持的ByteBuffer:

Now you can just create a ByteBuffer that is backed by this shared memory:

    // put it into a ByteBuffer so the java code can use it
    return env->NewDirectByteBuffer(myBuffer, bufferLength);
}

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