C++ 和 Java 进程之间的共享内存
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Shared memory between C++ and Java processes
提问by Brent Campbell
My aim is to pass data from a C++ process to a Java process and then to receive a result back.
我的目标是将数据从 C++ 进程传递到 Java 进程，然后接收返回的结果。
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.
我已经通过命名管道实现了这一点，但我更愿意共享数据而不是传递或复制它，假设访问速度会更快。
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.
最初，我想在 C++ 中创建一个共享段，我可以用 Java 写入和读取它，但我不确定这是否可以通过 JNI 实现，更不用说安全了。
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?
我相信在 Java 中可以使用 ByteBuffer.allocateDirect 分配内存，然后使用 GetDirectBufferAddress 访问 C++ 中的地址，但如果我是正确的，这是针对 JNI 中的本机调用，我无法在我的 C++ 进程中获取此地址?
Lost.
丢失。
Many thanks in advance.
提前谢谢了。
回答by main--
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 ByteBufferthat directlyaccesses the shared memory using NewDirectByteBufferlike this:
如果您有共享内存，例如使用CreateFileMapping(Windows) 或shmget(Unix)，您所需要的只是 Java 端的本机方法。然后，你可以创建一个ByteBuffer是直接使用访问共享内存NewDirectByteBuffer是这样的：
JNIEXPORT jobject JNICALL Java_getSharedBuffer(JNIEnv* env, jobject caller) {
void* myBuffer;
int bufferLength;
Now you have to get a pointer to the shared memory. On Windows you would use something like this:
现在你必须得到一个指向共享内存的指针。在 Windows 上，你会使用这样的东西：
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
Now you can just create a ByteBufferthat is backed by this shared memory:
现在你可以创建一个ByteBuffer由这个共享内存支持的：
// put it into a ByteBuffer so the java code can use it
return env->NewDirectByteBuffer(myBuffer, bufferLength);
}
回答by Shafik Yaghmour
Have you considered using 0MQit supports both Javaand C++and will be more reliable. I think if you want to do shared memory in Java it would have to be via JNI, last time I looked there was not other way to do it.
您是否考虑过使用0MQ，它同时支持Java和C++，并且会更可靠。我想如果你想在 Java 中做共享内存，它必须通过 JNI，上次我看没有其他方法可以做到这一点。
This shows you have to do it via JNIif you go that route. Although the solutions I have found are Windows specific which may not apply to you.
这表明如果你走那条路，你必须通过JNI来做。尽管我找到的解决方案是特定于 Windows 的，可能不适用于您。
