I am trying out the DJni library (https://github.com/Monnoroch/DJni). For some reason std.conv.to!string doesn't want to convert a char* to a string.The lines below are taken from the log. I see that the last frame is at gc_qalloc. I am not sure why it failed there. Can anybody elaborate on what is going on here ? Thanks in advance.

 91
 92
 93 Stack: [0x00007f749dfd9000,0x00007f749e0da000],  sp=0x00007f749e0d8600,  free space=1021k
 94 Native frames: (J=compiled Java code, j=interpreted, Vv=VM code, C=native code)
 95 C  [libPrompt.so+0x6b0cc]  gc_qalloc+0x2c
 96 C  [libPrompt.so+0x7bf18]  _D2rt8lifetime12__arrayAllocFNaNbmxC8TypeInfoxQlZS4core6memory8BlkInfo_+0xec
 97 C  [libPrompt.so+0x6c2fa]  _d_newarrayU+0x86
 98 C  [libPrompt.so+0x593a7]  _D6object__T4_dupTxaTaZQlFNaNbAxaZAa+0x1f
 99 C  [libPrompt.so+0x59384]  _D6object__T11_trustedDupTxaTaZQtFNaNbNeAxaZAa+0x20
100 C  [libPrompt.so+0x59360]  _D6object__T3dupTaZQhFNaNbNdNfAxaZAa+0x20
101 C  [libPrompt.so+0x5932a]  _D3std4conv__T6toImplTAyaTPxaZQqFQhZ9__lambda2MFNaNbZQBf+0x3e
102 C  [libPrompt.so+0x592ea]  _D3std4conv__T6toImplTAyaTPxaZQqFNaNbQlZQs+0x16
103 C  [libPrompt.so+0x592d1]  _D3std4conv__T2toTAyaZ__TQlTPxaZQsFNaNbQlZQy+0x9
104 C  [libPrompt.so+0x59289]  Java_Prompt_getLine+0x61
105 j  Prompt.getLine(Ljava/lang/String;)Ljava/lang/String;+0
106 j  Prompt.main([Ljava/lang/String;)V+11
107 v  ~StubRoutines::call_stub
108 V  [libjvm.so+0x690c66]  JavaCalls::call_helper(JavaValue*, methodHandle*, JavaCallArguments*, Thread*)+0x1056
109 V  [libjvm.so+0x6d2072]  jni_invoke_static(JNIEnv_*, JavaValue*, _jobject*, JNICallType, _jmethodID*, JNI_ArgumentPusher*, Thread*)+0x362
110 V  [libjvm.so+0x6ee8da]  jni_CallStaticVoidMethod+0x17a
111 C  [libjli.so+0x7bdf]  JavaMain+0x81f
112 C  [libpthread.so.0+0x8184]  start_thread+0xc4
113
114 Java frames: (J=compiled Java code, j=interpreted, Vv=VM code)
115 j  Prompt.getLine(Ljava/lang/String;)Ljava/lang/String;+0
116 j  Prompt.main([Ljava/lang/String;)V+11

On Saturday, 9 December 2017 at 05:55:21 UTC, Venkat wrote:
> I am trying out the DJni library (https://github.com/Monnoroch/DJni). For some reason std.conv.to!string doesn't want to convert a char* to a string.The lines below are taken from the log. I see that the last frame is at gc_qalloc. I am not sure why it failed there. Can anybody elaborate on what is going on here ? Thanks in advance.

I've got no idea, but can you verify that you can print it with printf? Can you allocate other GC memory? Can you try using fromStringz instead of to!string and see what that does?

Just shots in the dark...

Thanks for the quick response. std.string.fromStringz did the trick. I am not sure what was the deal with to!string.

On Saturday, 9 December 2017 at 06:14:36 UTC, Venkat wrote:
> Thanks for the quick response. std.string.fromStringz did the trick. I am not sure what was the deal with to!string.

Be careful with fromStringz. It doesn't allocate a new string, so the returned string can easily become corrupted if the C string it's referencing falls off the stack.

As for your problem with to!string, it isn't actually to!string that's the issue. It appears to have something to do with the memory allocated from the GC. I assume this is a shared library. Random thoughts -- Have you initialized DRuntime? Have you registered the calling thread with the GC?

Thank you, core.runtime.Runtime.initialize() fixed the issue. I am now able to use to!string as well. I found your posts and Ali Çehreli's posts on this subject. I think I have some understanding now.