JNA分配缓冲区FIXED_INFO抛出无效内存访问

Question

我有一个对新FIXED_INFO(缓冲区(的简单调用，导致java.lang.Error：无效内存访问。我一辈子都想不出为什么会失败：

import com.sun.jna.platform.win32.IPHlpAPI;
import com.sun.jna.platform.win32.IPHlpAPI.FIXED_INFO;
public void fixedInfoTest() {
int bufferSize = 648;
Memory buffer = new Memory(bufferSize);
FIXED_INFO fixedInfo = new FIXED_INFO(buffer);
}

在"new FIXED_INFO(buffer("调用中引发异常。

java.lang.Error: Invalid memory access
at com.sun.jna.Native._getPointer(Native Method)
at com.sun.jna.Native.getPointer(Native.java:2211)
at com.sun.jna.Pointer.getPointer(Pointer.java:642)
at com.sun.jna.Pointer.getValue(Pointer.java:367)
at com.sun.jna.Structure.readField(Structure.java:732)
at com.sun.jna.Structure.read(Structure.java:591)
at com.sun.jna.Structure.autoRead(Structure.java:2141)
at com.sun.jna.Structure.conditionalAutoRead(Structure.java:561)
at com.sun.jna.Structure.updateStructureByReference(Structure.java:690)
at com.sun.jna.Pointer.getValue(Pointer.java:367)
at com.sun.jna.Structure.readField(Structure.java:732)
at com.sun.jna.Structure.read(Structure.java:591)
at com.sun.jna.platform.win32.IPHlpAPI$FIXED_INFO.<init>(IPHlpAPI.java:208)
at com.magnicomp.test.unit.WindowsNativeTest.fixedInfoTest(WindowsNativeTest.java:43)

上述测试有时确实有效，但经常失败。测试系统是Win 10，Win Server 2016。JNA版本5.4.0

在我的生产代码中，fixedInfo用于：

IntByReference bufferSize = new IntByReference();
int result = IPHlpAPI.INSTANCE.GetNetworkParams(Pointer.NULL, bufferSize);
Validate.isTrue(result == WinNT.ERROR_BUFFER_OVERFLOW, 
"GetNetworkParams buffer size failed: " + Win32Error.getErrorMessage(result));      
Memory buffer = new Memory(bufferSize.getValue());
FIXED_INFO fixedInfo = new FIXED_INFO(buffer);
result = IPHlpAPI.INSTANCE.GetNetworkParams(fixedInfo.getPointer(), bufferSize);
if (result != WinNT.ERROR_SUCCESS) {
log.error("GetNetworkParams failed: %s", Win32Error.getErrorMessage(result));
return;
}
String domain = new String(fixedInfo.DomainName).trim(); 
log.info("GetNetworkParams gave domain="%s"", domain);

以下是我发现的一些例子：

https://www.javatips.net/api/oshi-master/oshi-core/src/main/java/oshi/software/os/windows/WindowsNetworkParams.java

Answer 1

问题是，您向FIXED_INFO的构造函数提供了一个Memory实例——该构造函数用于在结构中包含正确数据的内存，而您只是传递空的未初始化内存。FIXED_INFO的构造函数将尝试读取结构和其中的指针，并发现结构中的数据无效。

您应该调用FIXED_INFO的构造函数，该构造函数不接受任何参数。此构造函数将分配适当数量的内存，并为您正确初始化它。

将您的代码更改为：

// Memory buffer = new Memory(bufferSize); -- remove this line
FIXED_INFO fixedInfo = new FIXED_INFO();

这些信息的来源：查看JNA的源代码和包含FIXED_INFO的库。

• JNAStructure类(来自您的堆栈(
• FIXED_INFO

Answer 2

我想明白了。此代码有效：

IntByReference bufferSize = new IntByReference();
int result = IPHlpAPI.INSTANCE.GetNetworkParams(Pointer.NULL, bufferSize);
Validate.isTrue(result == WinNT.ERROR_BUFFER_OVERFLOW, 
"GetNetworkParams buffer size failed: " + Win32Error.getErrorMessage(result));
log.info("BufferSize=%d", bufferSize.getValue());
Memory buffer = new Memory(bufferSize.getValue());
// Now retrieve the actual FIXED_INFO
result = IPHlpAPI.INSTANCE.GetNetworkParams(buffer, bufferSize);
if (result != WinNT.ERROR_SUCCESS) {
log.error("GetNetworkParams failed: %s", Win32Error.getErrorMessage(result));
return;
}
FIXED_INFO fixedInfo = new FIXED_INFO(buffer);
String domain = new String(fixedInfo.DomainName).trim(); 
log.info("GetNetworkParams gave domain="%s"", domain);