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{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Segmentation faults with concurrent access?","articleBody":"Hello again!\n\nWhile developing https://github.com/papandreou/node-gitfakefs I stumbled upon what seems to be a bug in nodegit caused by calling the library asynchronously without waiting for the previous operation to finish.\n\nThe problem is triggered by a specific test in my test suite, and I was able to get a backtrace with gdb:\n\n```\nandreas@andreas-ThinkPad-T500:~/work/node-gitfakefs$ gdb --args ./node_modules/mocha/bin/mocha\nGNU gdb (Ubuntu/Linaro 7.4-2012.04-0ubuntu2.1) 7.4-2012.04\nCopyright (C) 2012 Free Software Foundation, Inc.\nLicense GPLv3+: GNU GPL version 3 or later \u003chttp://gnu.org/licenses/gpl.html\u003e\nThis is free software: you are free to change and redistribute it.\nThere is NO WARRANTY, to the extent permitted by law.  Type \"show copying\"\nand \"show warranty\" for details.\nThis GDB was configured as \"i686-linux-gnu\".\nFor bug reporting instructions, please see:\n\u003chttp://bugs.launchpad.net/gdb-linaro/\u003e...\n\"/home/andreas/work/node-gitfakefs/node_modules/mocha/bin/mocha\": not in executable format: File format not recognized\n(gdb) run\nStarting program: /home/andreas/.local/bin/node ./node_modules/mocha/bin/mocha\n[Thread debugging using libthread_db enabled]\nUsing host libthread_db library \"/lib/i386-linux-gnu/libthread_db.so.1\".\n[New Thread 0xb7fdab40 (LWP 32315)]\n\n  ․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․․\nProgram received signal SIGSEGV, Segmentation fault.\n0xb7fdd424 in __kernel_vsyscall ()\n(gdb) backtrace\n#0  0xb7fdd424 in __kernel_vsyscall ()\n#1  0xb7cf2526 in kill () from /lib/i386-linux-gnu/libc.so.6\n#2  0x08206efc in uv_kill (pid=32314, signum=11) at ../deps/uv/src/unix/process.c:434\n#3  0x081a1031 in node::Kill(v8::Arguments const\u0026) ()\n#4  0x083100d9 in v8::internal::Builtin_HandleApiCall(v8::internal::(anonymous namespace)::BuiltinArguments\u003c(v8::internal::BuiltinExtraArguments)1\u003e, v8::internal::Isolate*) ()\n#5  0x4360a336 in ?? ()\n#6  0x4362a97c in ?? ()\n#7  0x50f12c3c in ?? ()\n#8  0x4360db41 in ?? ()\n#9  0x4362d328 in ?? ()\n#10 0x4360db41 in ?? ()\n#11 0x43621c32 in ?? ()\n#12 0x43612c2a in ?? ()\n#13 0x0833021d in v8::internal::Invoke(bool, v8::internal::Handle\u003cv8::internal::JSFunction\u003e, v8::internal::Handle\u003cv8::internal::Object\u003e, int, v8::internal::Handle\u003cv8::internal::Object\u003e*, bool*) ()\n#14 0x08331962 in v8::internal::Execution::Call(v8::internal::Handle\u003cv8::internal::Object\u003e, v8::internal::Handle\u003cv8::internal::Object\u003e, int, v8::internal::Handle\u003cv8::internal::Object\u003e*, bool*, bool) ()\n#15 0x082f396e in v8::Function::Call(v8::Handle\u003cv8::Object\u003e, int, v8::Handle\u003cv8::Value\u003e*) ()\n#16 0x081a2d45 in node::EmitExit(v8::Handle\u003cv8::Object\u003e) ()\n#17 0x081a3fe2 in node::Start(int, char**) ()\n#18 0x081986bb in main ()\n```\n\nTo reproduce it, clone papandreou/node-gitfakefs@613d0f16, `npm link` it against nodegit master, then run: `mocha -g glob`. That causes the segmentation fault at least half of the time.\n\nThe test has a lot of moving parts. I tried to narrow it down further, but I've been unsuccessful so far. I wanted to raise the issue here before spending more time on it, as one of you guys might immediately go ah-hah! when seeing that stacktrace.\n\nThe reason why I know it's related to concurrent access is that I found a workaround in papandreou/node-gitfakefs@358eac4: It's wrapping accesses to nodegit in a mutex.\n\nWhile debugging the issue I've also seen these weird errors, which seem to bear witness to some kind of memory corruption:\n\n```\n  1) GitWrappedFs patching the built-in fs module \"in-place\" should make the glob work on the contents directory:\n     Error: @��@��e 'refs/heads/d35056a9711a2497e8c6a957fa6f0d13cb94f8b1' not found\n\n  1) GitWrappedFs patching the built-in fs module \"in-place\" should make the glob work on the contents directory:\n     Error: Failed to open '/home/andreas/work/node-gitfakefs/test/testrepo.git/packed-refs': No such file or directory\n```\n\nLet me know if there's anything else I can do at this point.\n","author":{"url":"https://github.com/papandreou","@type":"Person","name":"papandreou"},"datePublished":"2013-10-07T16:15:16.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":10},"url":"https://github.com/104/nodegit/issues/104"}