title: C callback with JNA makes JRE crash
body: <p>I'm having problems handling callbacks in JNA.</p>
  
  <p>I'm trying to use a C API that uses callbacks to handle several session events (logged in, logged out, connection problem...).<br>
  The session object (called <code>sp_session</code>) is an opaque struct. All the callbacks are registered in a <code>sp_session_callbacks</code> structure. According to the API, I am supposed to declare the callbacks object, and put it into a Config object that I will provide when creating the <code>sp_session</code> object. If I don't want to use certain callbacks, I am supposed to initialize them with <code>null</code>. The API is using the <code>__stdcall</code> calling convention.</p>
  
  <p>Here is a snippet of the C header that's relevant to my problem:</p>
  
  <pre><code>#define SP_CALLCONV __stdcall
  
  typedef struct sp_session sp_session; ///&lt; Representation of a session
  
  typedef enum sp_error {
      SP_ERROR_OK                        = 0,  
      SP_ERROR_BAD_API_VERSION           = 1,
          /* More errors */
  } sp_error;
  
  typedef struct sp_session_callbacks {
      /**
       * Called when login has been processed and was successful
       */
      void (SP_CALLCONV *logged_in)(sp_session *session, sp_error error);
  
      /**
       * Called when logout has been processed. Either called explicitly
       * if you initialize a logout operation, or implicitly if there
       * is a permanent connection error
       *
       * @param[in]  session    Session
       */
      void (SP_CALLCONV *logged_out)(sp_session *session);
  
      /**
       * Called when there is a connection error, and the library has problems
       * reconnecting to the Spotify service. Could be called multiple times (as
       * long as the problem is present) 
       */
      void (SP_CALLCONV *connection_error)(sp_session *session, sp_error error);
  
      /* More callbacks */
  } sp_session_callbacks;
  
  /**
   * Initialize a session. The session returned will be initialized, but you will need
   * to log in before you can perform any other operation
   */
  SP_LIBEXPORT(sp_error) sp_session_create(const sp_session_config *config, sp_session **sess);
  </code></pre>
  
  <p>Here is my equivalent JNA code:</p>
  
  <p><strong>The sp_session object</strong></p>
  
  <pre><code>public class sp_session extends PointerType{
  
      public sp_session(Pointer address) {
          super(address);
      }
      public sp_session() {
          super();
      }
  }
  </code></pre>
  
  <p><strong>The sp_session_callbacks object, containing all the callbacks</strong></p>
  
  <pre><code>public class sp_session_callbacks extends Structure{
      public LoggedIn logged_in;
      public LoggedOut logged_out;
      public ConnectionError connection_error;
  }
  </code></pre>
  
  <p><strong>The callbacks object (here is LoggedIn, but of course I have one for each callback)</strong></p>
  
  <pre><code>public interface LoggedIn extends StdCallCallback {
      public void logged_in(sp_session session, int error);
  }
  </code></pre>
  
  <p><strong>The native library, with the declaration of all the methods</strong></p>
  
  <pre><code>public interface JLibspotify extends StdCallLibrary{
      int sessionCreate(sp_session_config config, PointerByReference sess);
      int sessionLogin(sp_session session, String username, String password);
      // All the other methods defined by the API
  }
  </code></pre>
  
  <p><strong>And my main class, binding it all together</strong></p>
  
  <pre><code>public class Test{
      static{
          System.loadLibrary("libspotify");
      }
  
      public static void main(String[] args){
          JLibspotify lib = (JLibspotify)Native.loadLibrary("libspotify", JLibspotify.class);
          sp_session_config cfg = new sp_session_config();
          }
          sp_session_callbacks sessCallbacks = new sp_session_callbacks();
          LoggedIn loggedInCallback = new LoggedIn(){
          public void logged_in(sp_session session, int error) {
               System.out.println("logged_in() called");
              }
  
          };
          sessCallbacks.logged_in = loggedInCallback;
  
          cfg.session_callbacks = sessCallbacks;
  
          PointerByReference sessionPbr = new PointerByReference();
  
          int error_id = sessionCreate(cfg, sessionPbr); // CRASHES HERE
  
          sp_session mySession = new sp_session(sessionPbr.getValue());
      }
  }
  </code></pre>
  
  <p>So, the sessionCreate function call makes the JRE crash with the trace at the end of the post <code>EXCEPTION_ACCESS_VIOLATION (0xc0000005) problematic frame: C  [jna3666290841889849729.dll+0xa3f4]</code>.</p>
  
  <p>It looks like the logged_in callback is causing this, because when I set it to <code>null</code> it runs ok. Plus, if I initialize the <code>connection_error</code> callback, that has the exact same signature, it doesn't crash either.</p>
  
  <p>I'm running version 3.2.7 of JNA. I tried with an anterior version (3.0.9) and it also failed.
  I'm running the JDK 1.7 beta version, but I tried with the 1.6 and it also failed.</p>
  
  <p>Thank you!</p>
  
  <pre><code>#
  # A fatal error has been detected by the Java Runtime Environment:
  #
  #  EXCEPTION_ACCESS_VIOLATION (0xc0000005) at pc=0x0499a3f4, pid=1368, tid=1344
  #
  # JRE version: 7.0-b129
  # Java VM: Java HotSpot(TM) Client VM (21.0-b01 mixed mode, sharing windows-x86 )
  # Problematic frame:
  # C  [jna3666290841889849729.dll+0xa3f4]
  #
  # If you would like to submit a bug report, please visit:
  #   http://java.sun.com/webapps/bugreport/crash.jsp
  # The crash happened outside the Java Virtual Machine in native code.
  # See problematic frame for where to report the bug.
  #
  
  ---------------  T H R E A D  ---------------
  
  Current thread (0x01b79400):  JavaThread "main" [_thread_in_native, id=1344, stack(0x00340000,0x00390000)]
  
  siginfo: ExceptionCode=0xc0000005, reading address 0x1993053a
  
  Registers:
  EAX=0x19930522, EBX=0x100dc77c, ECX=0x00010004, EDX=0x1008d3e0
  ESP=0x0038f58c, EBP=0x0038f5b4, ESI=0x0038f5a4, EDI=0x100b79b0
  EIP=0x0499a3f4, EFLAGS=0x00210212
  
  Top of Stack: (sp=0x0038f58c)
  0x0038f58c:   100dc77c 0038f5a4 00010004 0038f688
  0x0038f59c:   05983de0 05981330 0598289c 05983de0
  0x0038f5ac:   05983de0 00000014 0038f688 1008d3ea
  0x0038f5bc:   05983de0 10030d77 0038fc44 100b79b0
  0x0038f5cc:   ffffffff 1008d334 00000000 05983de0
  0x0038f5dc:   1008d3e0 05983fc4 1008d9fd 0038f770
  0x0038f5ec:   00000000 00000000 7275016a 055310b0
  0x0038f5fc:   00000000 00010001 00000000 00000000 
  
  Instructions: (pc=0x0499a3f4)
  0x0499a3d4:   01 00 89 e5 57 56 8d 75 f0 53 83 ec 1c 8b 7d 14
  0x0499a3e4:   8b 5f 4c 8b 03 89 4c 24 08 89 74 24 04 89 1c 24
  0x0499a3f4:   ff 50 18 83 ec 0c 85 c0 0f 94 c0 0f b6 c0 85 c0
  0x0499a404:   89 45 ec 75 19 8b 03 31 d2 89 54 24 08 89 74 24 
  
  
  Register to memory mapping:
  
  EAX=0x19930522 is an unknown value
  EBX=0x100dc77c is an unknown value
  ECX=0x00010004 is an unknown value
  EDX=0x1008d3e0 is an unknown value
  ESP=0x0038f58c is pointing into the stack for thread: 0x01b79400
  EBP=0x0038f5b4 is pointing into the stack for thread: 0x01b79400
  ESI=0x0038f5a4 is pointing into the stack for thread: 0x01b79400
  EDI=0x100b79b0 is an unknown value
  
  
  Stack: [0x00340000,0x00390000],  sp=0x0038f58c,  free space=317k
  Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
  C  [jna3666290841889849729.dll+0xa3f4]  Java_com_sun_jna_Native_initialize_1ffi_1type+0x1054
  C  [libspotify.dll+0x8d3ea]  sp_error_message+0x35a
  C  [jna3666290841889849729.dll+0xcb77]  Java_com_sun_jna_Native_initialize_1ffi_1type+0x37d7
  C  [jna3666290841889849729.dll+0xc7c2]  Java_com_sun_jna_Native_initialize_1ffi_1type+0x3422
  C  [jna3666290841889849729.dll+0x4561]  Java_com_sun_jna_Pointer__1getString+0xa31
  C  [jna3666290841889849729.dll+0x4d2e]  Java_com_sun_jna_Function_invokeInt+0x2e
  j  com.sun.jna.Function.invokeInt(I[Ljava/lang/Object;)I+0
  j  com.sun.jna.Function.invoke([Ljava/lang/Object;Ljava/lang/Class;Z)Ljava/lang/Object;+315
  j  com.sun.jna.Function.invoke(Ljava/lang/Class;[Ljava/lang/Object;Ljava/util/Map;)Ljava/lang/Object;+214
  j  com.sun.jna.Library$Handler.invoke(Ljava/lang/Object;Ljava/lang/reflect/Method;[Ljava/lang/Object;)Ljava/lang/Object;+341
  j  $Proxy0.sp_session_create(Lcom/nbarraille/jspotify/model/sp_session_config;Lcom/sun/jna/ptr/PointerByReference;)I+20
  j  com.nbarraille.jspotify.main.Test.main([Ljava/lang/String;)V+273
  v  ~StubRoutines::call_stub
  V  [jvm.dll+0x115f6d]
  V  [jvm.dll+0x1b788e]
  V  [jvm.dll+0x115fed]
  V  [jvm.dll+0xa2507]
  V  [jvm.dll+0xac867]
  C  [javaw.exe+0x209e]
  C  [javaw.exe+0xa23b]
  C  [javaw.exe+0xa2c5]
  C  [kernel32.dll+0x51194]  BaseThreadInitThunk+0x12
  C  [ntdll.dll+0x5b429]  RtlInitializeExceptionChain+0x63
  C  [ntdll.dll+0x5b3fc]  RtlInitializeExceptionChain+0x36
  
  Java frames: (J=compiled Java code, j=interpreted, Vv=VM code)
  j  com.sun.jna.Function.invokeInt(I[Ljava/lang/Object;)I+0
  j  com.sun.jna.Function.invoke([Ljava/lang/Object;Ljava/lang/Class;Z)Ljava/lang/Object;+315
  j  com.sun.jna.Function.invoke(Ljava/lang/Class;[Ljava/lang/Object;Ljava/util/Map;)Ljava/lang/Object;+214
  j  com.sun.jna.Library$Handler.invoke(Ljava/lang/Object;Ljava/lang/reflect/Method;[Ljava/lang/Object;)Ljava/lang/Object;+341
  j  $Proxy0.sp_session_create(Lcom/nbarraille/jspotify/model/sp_session_config;Lcom/sun/jna/ptr/PointerByReference;)I+20
  j  com.nbarraille.jspotify.main.Test.main([Ljava/lang/String;)V+273
  v  ~StubRoutines::call_stub
  
  ---------------  P R O C E S S  ---------------
  
  Java Threads: ( =&gt; current thread )
    0x0182fc00 JavaThread "Low Memory Detector" daemon [_thread_blocked, id=4664, stack(0x04170000,0x041c0000)]
    0x0182ac00 JavaThread "C1 CompilerThread0" daemon [_thread_blocked, id=1728, stack(0x01b20000,0x01b70000)]
    0x01829800 JavaThread "Attach Listener" daemon [_thread_blocked, id=112, stack(0x04020000,0x04070000)]
    0x01826400 JavaThread "Signal Dispatcher" daemon [_thread_blocked, id=5836, stack(0x03ea0000,0x03ef0000)]
    0x01819800 JavaThread "Finalizer" daemon [_thread_blocked, id=4724, stack(0x03f80000,0x03fd0000)]
    0x01817800 JavaThread "Reference Handler" daemon [_thread_blocked, id=3940, stack(0x01ad0000,0x01b20000)]
  =&gt;0x01b79400 JavaThread "main" [_thread_in_native, id=1344, stack(0x00340000,0x00390000)]
  
  Other Threads:
    0x01816400 VMThread [stack: 0x01a30000,0x01a80000] [id=3876]
    0x01843000 WatcherThread [stack: 0x040d0000,0x04120000] [id=4636]
  
  VM state:not at safepoint (normal execution)
  
  VM Mutex/Monitor currently owned by a thread: None
  
  Heap
   def new generation   total 4928K, used 3630K [0x23450000, 0x239a0000, 0x289a0000)
    eden space 4416K,  82% used [0x23450000, 0x237db858, 0x238a0000)
    from space 512K,   0% used [0x238a0000, 0x238a0000, 0x23920000)
    to   space 512K,   0% used [0x23920000, 0x23920000, 0x239a0000)
   tenured generation   total 10944K, used 0K [0x289a0000, 0x29450000, 0x33450000)
     the space 10944K,   0% used [0x289a0000, 0x289a0000, 0x289a0200, 0x29450000)
   compacting perm gen  total 12288K, used 860K [0x33450000, 0x34050000, 0x37450000)
     the space 12288K,   7% used [0x33450000, 0x33527190, 0x33527200, 0x34050000)
      ro space 10240K,  43% used [0x37450000, 0x3789ce40, 0x3789d000, 0x37e50000)
      rw space 12288K,  53% used [0x37e50000, 0x384c2710, 0x384c2800, 0x38a50000)
  
  Code Cache  [0x01e90000, 0x01f20000, 0x03e90000)
   total_blobs=234 nmethods=82 adapters=88 free_code_cache=32972224 largest_free_block=0
  
  Dynamic libraries:
  0x00880000 - 0x008b0000     C:\Program Files\Java\jdk1.7.0\bin\javaw.exe
  0x778f0000 - 0x77a2d000     C:\Windows\SYSTEM32\ntdll.dll
  0x77070000 - 0x77144000     C:\Windows\system32\kernel32.dll
  0x75cf0000 - 0x75d3a000     C:\Windows\system32\KERNELBASE.dll
  0x60000000 - 0x60041000     C:\Program Files\BitDefender\BitDefender 2011\Active Virus Control\Midas_00078_002\midas32.dll
  0x61000000 - 0x61028000     C:\Program Files\BitDefender\BitDefender 2011\Active Virus Control\Midas_00078_002\plugin_base.m32
  0x67000000 - 0x67048000     C:\Program Files\BitDefender\BitDefender 2011\Active Virus Control\Midas_00078_002\plugin_nt.m32
  0x64000000 - 0x64021000     C:\Program Files\BitDefender\BitDefender 2011\Active Virus Control\Midas_00078_002\plugin_registry.m32
  0x62000000 - 0x6202d000     C:\Program Files\BitDefender\BitDefender 2011\Active Virus Control\Midas_00078_002\plugin_extra.m32
  0x65000000 - 0x6501a000     C:\Program Files\BitDefender\BitDefender 2011\Active Virus Control\Midas_00078_002\plugin_net.m32
  0x63000000 - 0x630a6000     C:\Program Files\BitDefender\BitDefender 2011\Active Virus Control\Midas_00078_002\plugin_fragments.m32
  0x75e10000 - 0x75eb0000     C:\Windows\system32\ADVAPI32.dll
  0x775c0000 - 0x7766c000     C:\Windows\system32\msvcrt.dll
  0x75d50000 - 0x75d69000     C:\Windows\SYSTEM32\sechost.dll
  0x77670000 - 0x77711000     C:\Windows\system32\RPCRT4.dll
  0x76f00000 - 0x76fc9000     C:\Windows\system32\USER32.dll
  0x77a50000 - 0x77a9e000     C:\Windows\system32\GDI32.dll
  0x77a30000 - 0x77a3a000     C:\Windows\system32\LPK.dll
  0x75d70000 - 0x75e0d000     C:\Windows\system32\USP10.dll
  0x74830000 - 0x749ce000     C:\Windows\WinSxS\x86_microsoft.windows.common-controls_6595b64144ccf1df_6.0.7600.16661_none_420fe3fa2b8113bd\COMCTL32.dll
  0x772f0000 - 0x77347000     C:\Windows\system32\SHLWAPI.dll
  0x775a0000 - 0x775bf000     C:\Windows\system32\IMM32.DLL
  0x75eb0000 - 0x75f7c000     C:\Windows\system32\MSCTF.dll
  0x72740000 - 0x727fe000     C:\Program Files\Java\jdk1.7.0\jre\bin\msvcr100.dll
  0x01b80000 - 0x01e89000     C:\Program Files\Java\jdk1.7.0\jre\bin\client\jvm.dll
  0x746c0000 - 0x746f2000     C:\Windows\system32\WINMM.dll
  0x73920000 - 0x7392c000     C:\Program Files\Java\jdk1.7.0\jre\bin\verify.dll
  0x73330000 - 0x73350000     C:\Program Files\Java\jdk1.7.0\jre\bin\java.dll
  0x75d40000 - 0x75d45000     C:\Windows\system32\PSAPI.DLL
  0x733a0000 - 0x733b3000     C:\Program Files\Java\jdk1.7.0\jre\bin\zip.dll
  0x10000000 - 0x10259000     C:\Windows\System32\libspotify.dll
  0x77150000 - 0x77185000     C:\Windows\system32\WS2_32.dll
  0x77a40000 - 0x77a46000     C:\Windows\system32\NSI.dll
  0x75ba0000 - 0x75cbc000     C:\Windows\system32\CRYPT32.dll
  0x75ab0000 - 0x75abc000     C:\Windows\system32\MSASN1.dll
  0x74ee0000 - 0x74f38000     C:\Windows\system32\WINHTTP.dll
  0x74e90000 - 0x74edf000     C:\Windows\system32\webio.dll
  0x754c0000 - 0x754d6000     C:\Windows\system32\CRYPTSP.dll
  0x75260000 - 0x7529b000     C:\Windows\system32\rsaenh.dll
  0x750a0000 - 0x750b7000     C:\Windows\system32\USERENV.dll
  0x75a40000 - 0x75a4b000     C:\Windows\system32\profapi.dll
  0x75a30000 - 0x75a3c000     C:\Windows\system32\CRYPTBASE.dll
  0x728a0000 - 0x728b6000     C:\Program Files\Java\jdk1.7.0\jre\bin\net.dll
  0x75480000 - 0x754bc000     C:\Windows\system32\mswsock.dll
  0x75470000 - 0x75476000     C:\Windows\System32\wship6.dll
  0x73950000 - 0x73960000     C:\Windows\system32\NLAapi.dll
  0x75340000 - 0x75384000     C:\Windows\system32\DNSAPI.dll
  0x71030000 - 0x71038000     C:\Windows\System32\winrnr.dll
  0x71020000 - 0x71030000     C:\Windows\system32\napinsp.dll
  0x71000000 - 0x71012000     C:\Windows\system32\pnrpnsp.dll
  0x74fd0000 - 0x74fd5000     C:\Windows\System32\wshtcpip.dll
  0x74d30000 - 0x74d4c000     C:\Windows\system32\IPHLPAPI.DLL
  0x74d20000 - 0x74d27000     C:\Windows\system32\WINNSI.DLL
  0x70c60000 - 0x70c66000     C:\Windows\system32\rasadhlp.dll
  0x71ba0000 - 0x71bd8000     C:\Windows\System32\fwpuclnt.dll
  0x73930000 - 0x7393f000     C:\Program Files\Java\jdk1.7.0\jre\bin\nio.dll
  0x04990000 - 0x049e5000     C:\Users\nbarraille\AppData\Local\Temp\jna3666290841889849729.dll
  
  VM Arguments:
  jvm_args: -Djava.library.path=C:\Windows\System32 -Dfile.encoding=Cp1252 
  java_command: com.nbarraille.jspotify.main.Test
  Launcher Type: SUN_STANDARD
  
  Environment Variables:
  PATH=C:/Program Files/Java/jdk1.7.0/bin/../jre/bin/client;C:/Program Files/Java/jdk1.7.0/bin/../jre/bin;C:/Program Files/Java/jdk1.7.0/bin/../jre/lib/i386;C:\Windows\System32
  USERNAME=nbarraille
  OS=Windows_NT
  PROCESSOR_IDENTIFIER=x86 Family 6 Model 23 Stepping 10, GenuineIntel
  
  
  
  ---------------  S Y S T E M  ---------------
  
  OS: Windows 7 Build 7600 
  
  CPU:total 2 (2 cores per cpu, 1 threads per core) family 6 model 23 stepping 10, cmov, cx8, fxsr, mmx, sse, sse2, sse3, ssse3, sse4.1
  
  Memory: 4k page, physical 3624108k(885020k free), swap 7246452k(3637664k free)
  
  vm_info: Java HotSpot(TM) Client VM (21.0-b01) for windows-x86 JRE (1.7.0-ea-b129), built on Feb 10 2011 07:43:39 by "java_re" with unknown MS VC++:1600
  
  time: Mon Mar 07 14:25:08 2011
  elapsed time: 0 seconds
  </code></pre>
  
  <p><strong>EDIT:</strong>
  *<em>Code to test the API in C</em>*</p>
  
  <pre><code>#include "api.h"
  
  
  /* --- Data --- */
  const uint8_t g_appkey[] = {/*My appkey*/};
  
  
  /* ---------------------------  SESSION CALLBACKS  ------------------------- */
  static void logged_in(sp_session *sess, sp_error error){
      printf("logged_in() called: \n");
  }
  
  static void log_message(sp_session *sess, const char *data){
      printf("log_message() called %s : \n", data);
  }
  
  static void notify_main_thread(sp_session *sess){
      printf("notify_main_thread() called \n");
  }
  
  static sp_session_callbacks session_callbacks = {
      //.logged_in = (void*)&amp;logged_in,
      //.notify_main_thread = (void*)&amp;notify_main_thread,
      //.log_message = (void*)&amp;log_message,
  };
  
  static sp_session_config spconfig = {
      .api_version = 7,
      .cache_location = "tmp",
      .settings_location = "tmp",
      .application_key = g_appkey,
      .application_key_size = sizeof(g_appkey),
      .user_agent = "jspotify",
      .callbacks = &amp;session_callbacks,
      .userdata = NULL
  };
  
  int main(int argc, char **argv)
  {
      sp_session *sp;
  
      const char *username = "foo";
      const char *password = "bar";
  
      spconfig.application_key_size = sizeof(g_appkey);
  
  
      printf("Creating session \n");
  
      sp_error err = sp_session_create(&amp;spconfig, &amp;sp);
  
      if(err != 0){
          printf("Error occured: %d \n", err);
          return 0;
      }
  
      printf("Login\n");
      sp_session_login(sp, username, password);
  
      Sleep(10000);
      return 0;
  }
  </code></pre>
  
  <p>When I run it like this (without callbacks), the output is:</p>
  
  <pre><code>Creating session 
  Login
  </code></pre>
  
  <p>And when I register the callbacks (uncomment the lines), it doesn't even print anything!</p>
  
  <p>It looks like it doesn't print anything when a callback is called, because if I comment the <code>sp_session_login</code> line, only the declaration of <code>notify_main_thread</code> (which is the only one printed) will prevent the program from printing...</p>