我面临一个只在
Windows上发生的有趣问题,而在
Linux / Mono上一切正常.我已经构建了一个围绕
MySQL Cluster NDB API库的C包装器,我通过P / Invoke从C#代码调用它.到目前为止,我有三种方法：
> init()初始化环境并返回句柄
> read()使用句柄从数据库中读取数据
> release(),它释放资源
init()在每个设置中都能正常工作.但是,read()抛出AccessViolationException,但仅在Windows上,并且只有在一个线程中调用init()而在另一个线程中调用read()时才会抛出.如果我们在一个线程中做所有事情,那就有效！任何关于可能原因的想法将不胜感激.
2016年12月4日更新 – 使用简单的C测试程序注意到相同的行为,其中init()在一个线程中调用,而read()在另一个线程中调用.因此,错误与C#/ C interop无关,它可以在NDB API库中下载here(lib文件夹,MysqLclient.lib和ndbclient_static.lib).
C#代码：
private const string ndbapi = "ndb";
[DllImport(ndbapi)]
public extern static IntPtr init(IntPtr conn_string);
[DllImport(ndbapi)]
public extern static void read(IntPtr ndb_cluster_conn);
[DllImport(ndbapi)]
public extern static void release(IntPtr ndb_cluster_conn,IntPtr char_arr_ptr);
private static IntPtr handle;
private static void InitNdb() {
unsafe {
fixed (byte* conn_buf = Encoding.UTF8.GetBytes("node1:1186")) {
handle = ndb_api_init(new IntPtr(conn_buf));
}
}
}
static void Main(string[] args) {
Thread t = new Thread(InitNdb);// IF I CALL InitNDB IN THE SAME THREAD,EVERYTHING WORKS
t.Start();
.. //waiting for Thread t to complete...
IntPtr bytes_read = read(handle);
...
}
C代码:(基于official documentation的例子)：
#if defined(WIN32)
#define DLLEXPORT __declspec(dllexport)
#define CALLCV __stdcall
#else
#define DLLEXPORT __attribute__((visibility("default")))
#define CALLCV __attribute__((cdecl))
#endif
..
extern "C" DLLEXPORT Ndb_cluster_connection* CALLCV init(char* connection_string) {
ndb_init();
// Object representing the cluster
Ndb_cluster_connection* cluster_connection = new Ndb_cluster_connection(connection_string);
if (cluster_connection->connect(3,2,1)) {
std::cout << "Cluster management server not ready,error:" << cluster_connection->get_latest_error_msg() << "\n";
exit(-1);
}
if (cluster_connection->wait_until_ready(10,0) < 0) {
std::cout << "Cluster not ready within 10 secs,error:" << cluster_connection->get_latest_error_msg() << std::endl;
}
return cluster_connection;
}
extern "C" DLLEXPORT char** CALLCV read(Ndb_cluster_connection* cluster_connection) {
Ndb *ndb_obj = new Ndb(cluster_connection,db_name);
if (ndb_obj->init()) {
std::cout << "Error while initializing Ndb " << std::endl;
}
const NdbDictionary::Dictionary* dict = ndb_obj->getDictionary();
const NdbDictionary::Table *table = dict->getTable("table_name"); <-- THIS IS THE LINE THAT THROWS ACCESS VIOLATION EXCEPTION
..
}
