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<html lang="en"><head><meta charset="UTF-8"/><meta name="viewport" content="width=device-width, initial-scale=1.0"/><title>Initialization of the Julia runtime · The Julia Language</title><script>(function(i,s,o,g,r,a,m){i['GoogleAnalyticsObject']=r;i[r]=i[r]||function(){
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</script><link href="https://cdnjs.cloudflare.com/ajax/libs/normalize/4.2.0/normalize.min.css" rel="stylesheet" type="text/css"/><link href="https://fonts.googleapis.com/css?family=Lato|Roboto+Mono" rel="stylesheet" type="text/css"/><link href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.6.3/css/font-awesome.min.css" rel="stylesheet" type="text/css"/><link href="https://cdnjs.cloudflare.com/ajax/libs/highlight.js/9.12.0/styles/default.min.css" rel="stylesheet" type="text/css"/><script>documenterBaseURL=".."</script><script src="https://cdnjs.cloudflare.com/ajax/libs/require.js/2.2.0/require.min.js" data-main="../assets/documenter.js"></script><script src="../siteinfo.js"></script><script src="../../versions.js"></script><link href="../assets/documenter.css" rel="stylesheet" type="text/css"/><link href="../assets/julia-manual.css" rel="stylesheet" type="text/css"/></head><body><nav class="toc"><a href="../index.html"><img class="logo" src="../assets/logo.png" alt="The Julia Language logo"/></a><h1>The Julia Language</h1><select id="version-selector" onChange="window.location.href=this.value" style="visibility: hidden"></select><form class="search" id="search-form" action="../search.html"><input id="search-query" name="q" type="text" placeholder="Search docs"/></form><ul><li><a class="toctext" href="../index.html">Home</a></li><li><span class="toctext">Manual</span><ul><li><a class="toctext" href="../manual/introduction.html">Introduction</a></li><li><a class="toctext" href="../manual/getting-started.html">Getting Started</a></li><li><a class="toctext" href="../manual/variables.html">Variables</a></li><li><a class="toctext" href="../manual/integers-and-floating-point-numbers.html">Integers and Floating-Point Numbers</a></li><li><a class="toctext" href="../manual/mathematical-operations.html">Mathematical Operations and Elementary Functions</a></li><li><a class="toctext" href="../manual/complex-and-rational-numbers.html">Complex and Rational 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href="../manual/embedding.html">Embedding Julia</a></li><li><a class="toctext" href="../manual/packages.html">Packages</a></li><li><a class="toctext" href="../manual/profile.html">Profiling</a></li><li><a class="toctext" href="../manual/stacktraces.html">Stack Traces</a></li><li><a class="toctext" href="../manual/performance-tips.html">Performance Tips</a></li><li><a class="toctext" href="../manual/workflow-tips.html">Workflow Tips</a></li><li><a class="toctext" href="../manual/style-guide.html">Style Guide</a></li><li><a class="toctext" href="../manual/faq.html">Frequently Asked Questions</a></li><li><a class="toctext" href="../manual/noteworthy-differences.html">Noteworthy Differences from other Languages</a></li><li><a class="toctext" href="../manual/unicode-input.html">Unicode Input</a></li></ul></li><li><span class="toctext">Standard Library</span><ul><li><a class="toctext" href="../stdlib/base.html">Essentials</a></li><li><a class="toctext" 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class="toctext" href="../stdlib/dates.html">Dates and Time</a></li><li><a class="toctext" href="../stdlib/iterators.html">Iteration utilities</a></li><li><a class="toctext" href="../stdlib/test.html">Unit Testing</a></li><li><a class="toctext" href="../stdlib/c.html">C Interface</a></li><li><a class="toctext" href="../stdlib/libc.html">C Standard Library</a></li><li><a class="toctext" href="../stdlib/libdl.html">Dynamic Linker</a></li><li><a class="toctext" href="../stdlib/profile.html">Profiling</a></li><li><a class="toctext" href="../stdlib/stacktraces.html">StackTraces</a></li><li><a class="toctext" href="../stdlib/simd-types.html">SIMD Support</a></li></ul></li><li><span class="toctext">Developer Documentation</span><ul><li><a class="toctext" href="reflection.html">Reflection and introspection</a></li><li><span class="toctext">Documentation of Julia's Internals</span><ul><li class="current"><a class="toctext" href="init.html">Initialization of the Julia runtime</a><ul class="internal"><li><a class="toctext" href="#main()-1">main()</a></li><li><a class="toctext" href="#julia_init()-1">julia_init()</a></li><li><a class="toctext" href="#true_main()-1">true_main()</a></li><li><a class="toctext" href="#Base._start-1">Base._start</a></li><li><a class="toctext" href="#Base.eval-1">Base.eval</a></li><li><a class="toctext" href="#jl_atexit_hook()-1">jl_atexit_hook()</a></li><li><a class="toctext" href="#julia_save()-1">julia_save()</a></li></ul></li><li><a class="toctext" href="ast.html">Julia ASTs</a></li><li><a class="toctext" href="types.html">More about types</a></li><li><a class="toctext" href="object.html">Memory layout of Julia Objects</a></li><li><a class="toctext" href="eval.html">Eval of Julia code</a></li><li><a class="toctext" href="callconv.html">Calling Conventions</a></li><li><a class="toctext" href="compiler.html">High-level Overview of the Native-Code Generation Process</a></li><li><a class="toctext" href="functions.html">Julia Functions</a></li><li><a class="toctext" href="cartesian.html">Base.Cartesian</a></li><li><a class="toctext" href="meta.html">Talking to the compiler (the <code>:meta</code> mechanism)</a></li><li><a class="toctext" href="subarrays.html">SubArrays</a></li><li><a class="toctext" href="sysimg.html">System Image Building</a></li><li><a class="toctext" href="llvm.html">Working with LLVM</a></li><li><a class="toctext" href="stdio.html">printf() and stdio in the Julia runtime</a></li><li><a class="toctext" href="boundscheck.html">Bounds checking</a></li><li><a class="toctext" href="locks.html">Proper maintenance and care of multi-threading locks</a></li><li><a class="toctext" href="offset-arrays.html">Arrays with custom indices</a></li><li><a class="toctext" href="libgit2.html">Base.LibGit2</a></li><li><a class="toctext" href="require.html">Module loading</a></li></ul></li><li><span class="toctext">Developing/debugging Julia's C code</span><ul><li><a class="toctext" href="backtraces.html">Reporting and analyzing crashes (segfaults)</a></li><li><a class="toctext" href="debuggingtips.html">gdb debugging tips</a></li><li><a class="toctext" href="valgrind.html">Using Valgrind with Julia</a></li><li><a class="toctext" href="sanitizers.html">Sanitizer support</a></li></ul></li></ul></li></ul></nav><article id="docs"><header><nav><ul><li>Developer Documentation</li><li>Documentation of Julia's Internals</li><li><a href="init.html">Initialization of the Julia runtime</a></li></ul><a class="edit-page" href="https://github.com/JuliaLang/julia/blob/master/doc/src/devdocs/init.md"><span class="fa"></span> Edit on GitHub</a></nav><hr/><div id="topbar"><span>Initialization of the Julia runtime</span><a class="fa fa-bars" href="#"></a></div></header><h1><a class="nav-anchor" id="Initialization-of-the-Julia-runtime-1" href="#Initialization-of-the-Julia-runtime-1">Initialization of the Julia runtime</a></h1><p>How does the Julia runtime execute <code>julia -e 'println("Hello World!")'</code> ?</p><h2><a class="nav-anchor" id="main()-1" href="#main()-1">main()</a></h2><p>Execution starts at <a href="https://github.com/JuliaLang/julia/blob/master/ui/repl.c"><code>main()</code> in <code>ui/repl.c</code></a>.</p><p><code>main()</code> calls <a href="https://github.com/JuliaLang/julia/blob/master/src/support/libsupportinit.c"><code>libsupport_init()</code></a> to set the C library locale and to initialize the "ios" library (see <a href="https://github.com/JuliaLang/julia/blob/master/src/support/ios.c"><code>ios_init_stdstreams()</code></a> and <a href="stdio.html#Legacy-ios.c-library-1">Legacy <code>ios.c</code> library</a>).</p><p>Next <a href="https://github.com/JuliaLang/julia/blob/master/ui/repl.c"><code>parse_opts()</code></a> is called to process command line options. Note that <code>parse_opts()</code> only deals with options that affect code generation or early initialization. Other options are handled later by <a href="https://github.com/JuliaLang/julia/blob/master/base/client.jl"><code>process_options()</code> in <code>base/client.jl</code></a>.</p><p><code>parse_opts()</code> stores command line options in the <a href="https://github.com/JuliaLang/julia/blob/master/src/julia.h">global <code>jl_options</code> struct</a>.</p><h2><a class="nav-anchor" id="julia_init()-1" href="#julia_init()-1">julia_init()</a></h2><p><a href="https://github.com/JuliaLang/julia/blob/master/src/task.c"><code>julia_init()</code> in <code>task.c</code></a> is called by <code>main()</code> and calls <a href="https://github.com/JuliaLang/julia/blob/master/src/init.c"><code>_julia_init()</code> in <code>init.c</code></a>.</p><p><code>_julia_init()</code> begins by calling <code>libsupport_init()</code> again (it does nothing the second time).</p><p><a href="https://github.com/JuliaLang/julia/blob/master/src/signals-unix.c"><code>restore_signals()</code></a> is called to zero the signal handler mask.</p><p><a href="https://github.com/JuliaLang/julia/blob/master/src/init.c"><code>jl_resolve_sysimg_location()</code></a> searches configured paths for the base system image. See <a href="sysimg.html#Building-the-Julia-system-image-1">Building the Julia system image</a>.</p><p><a href="https://github.com/JuliaLang/julia/blob/master/src/gc.c"><code>jl_gc_init()</code></a> sets up allocation pools and lists for weak refs, preserved values and finalization.</p><p><a href="https://github.com/JuliaLang/julia/blob/master/src/ast.c"><code>jl_init_frontend()</code></a> loads and initializes a pre-compiled femtolisp image containing the scanner/parser.</p><p><a href="https://github.com/JuliaLang/julia/blob/master/src/jltypes.c"><code>jl_init_types()</code></a> creates <code>jl_datatype_t</code> type description objects for the <a href="https://github.com/JuliaLang/julia/blob/master/src/julia.h">built-in types defined in <code>julia.h</code></a>. e.g.</p><pre><code class="language-c">jl_any_type = jl_new_abstracttype(jl_symbol("Any"), NULL, jl_null);
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jl_any_type->super = jl_any_type;
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jl_type_type = jl_new_abstracttype(jl_symbol("Type"), jl_any_type, jl_null);
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jl_int32_type = jl_new_bitstype(jl_symbol("Int32"),
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jl_any_type, jl_null, 32);</code></pre><p><a href="https://github.com/JuliaLang/julia/blob/master/src/task.c"><code>jl_init_tasks()</code></a> creates the <code>jl_datatype_t* jl_task_type</code> object; initializes the global <code>jl_root_task</code> struct; and sets <code>jl_current_task</code> to the root task.</p><p><a href="https://github.com/JuliaLang/julia/blob/master/src/codegen.cpp"><code>jl_init_codegen()</code></a> initializes the <a href="http://llvm.org">LLVM library</a>.</p><p><a href="https://github.com/JuliaLang/julia/blob/master/src/dump.c"><code>jl_init_serializer()</code></a> initializes 8-bit serialization tags for 256 frequently used <code>jl_value_t</code> values. The serialization mechanism uses these tags as shorthand (in lieu of storing whole objects) to save storage space.</p><p>If there is no sysimg file (<code>!jl_options.image_file</code>) then the <code>Core</code> and <code>Main</code> modules are created and <code>boot.jl</code> is evaluated:</p><p><code>jl_core_module = jl_new_module(jl_symbol("Core"))</code> creates the Julia <code>Core</code> module.</p><p><a href="https://github.com/JuliaLang/julia/blob/master/src/intrinsics.cpp"><code>jl_init_intrinsic_functions()</code></a> creates a new Julia module <code>Intrinsics</code> containing constant <code>jl_intrinsic_type</code> symbols. These define an integer code for each <a href="https://github.com/JuliaLang/julia/blob/master/src/intrinsics.cpp">intrinsic function</a>. <a href="https://github.com/JuliaLang/julia/blob/master/src/intrinsics.cpp"><code>emit_intrinsic()</code></a> translates these symbols into LLVM instructions during code generation.</p><p><a href="https://github.com/JuliaLang/julia/blob/master/src/builtins.c"><code>jl_init_primitives()</code></a> hooks C functions up to Julia function symbols. e.g. the symbol <code>Base.is()</code> is bound to C function pointer <code>jl_f_is()</code> by calling <code>add_builtin_func("eval", jl_f_top_eval)</code>.</p><p><a href="https://github.com/JuliaLang/julia/blob/master/src/toplevel.c"><code>jl_new_main_module()</code></a> creates the global "Main" module and sets <code>jl_current_task->current_module = jl_main_module</code>.</p><p>Note: <code>_julia_init()</code> <a href="https://github.com/JuliaLang/julia/blob/master/src/init.c">then sets</a> <code>jl_root_task->current_module = jl_core_module</code>. <code>jl_root_task</code> is an alias of <code>jl_current_task</code> at this point, so the <code>current_module</code> set by <code>jl_new_main_module()</code> above is overwritten.</p><p><a href="https://github.com/JuliaLang/julia/blob/master/src/init.c"><code>jl_load("boot.jl", sizeof("boot.jl"))</code></a> calls <a href="https://github.com/JuliaLang/julia/blob/master/src/ast.c"><code>jl_parse_eval_all</code></a> which repeatedly calls <a href="https://github.com/JuliaLang/julia/blob/master/src/toplevel.c"><code>jl_toplevel_eval_flex()</code></a> to execute <a href="https://github.com/JuliaLang/julia/blob/master/base/boot.jl"><code>boot.jl</code></a>. <!– TODO – drill down into eval? –></p><p><a href="https://github.com/JuliaLang/julia/blob/master/src/init.c"><code>jl_get_builtin_hooks()</code></a> initializes global C pointers to Julia globals defined in <code>boot.jl</code>.</p><p><a href="https://github.com/JuliaLang/julia/blob/master/src/datatype.c"><code>jl_init_box_caches()</code></a> pre-allocates global boxed integer value objects for values up to 1024. This speeds up allocation of boxed ints later on. e.g.:</p><pre><code class="language-c">jl_value_t *jl_box_uint8(uint32_t x)
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{
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return boxed_uint8_cache[(uint8_t)x];
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}</code></pre><p><a href="https://github.com/JuliaLang/julia/blob/master/src/init.c"><code>_julia_init()</code> iterates</a> over the <code>jl_core_module->bindings.table</code> looking for <code>jl_datatype_t</code> values and sets the type name's module prefix to <code>jl_core_module</code>.</p><p><a href="https://github.com/JuliaLang/julia/blob/master/src/toplevel.c"><code>jl_add_standard_imports(jl_main_module)</code></a> does "using Base" in the "Main" module.</p><p>Note: <code>_julia_init()</code> now reverts to <code>jl_root_task->current_module = jl_main_module</code> as it was before being set to <code>jl_core_module</code> above.</p><p>Platform specific signal handlers are initialized for <code>SIGSEGV</code> (OSX, Linux), and <code>SIGFPE</code> (Windows).</p><p>Other signals (<code>SIGINFO, SIGBUS, SIGILL, SIGTERM, SIGABRT, SIGQUIT, SIGSYS</code> and <code>SIGPIPE</code>) are hooked up to <a href="https://github.com/JuliaLang/julia/blob/master/src/signals-unix.c"><code>sigdie_handler()</code></a> which prints a backtrace.</p><p><a href="https://github.com/JuliaLang/julia/blob/master/src/dump.c"><code>jl_init_restored_modules()</code></a> calls <a href="https://github.com/JuliaLang/julia/blob/master/src/module.c"><code>jl_module_run_initializer()</code></a> for each deserialized module to run the <code>__init__()</code> function.</p><p>Finally <a href="https://github.com/JuliaLang/julia/blob/master/src/signals-unix.c"><code>sigint_handler()</code></a> is hooked up to <code>SIGINT</code> and calls <code>jl_throw(jl_interrupt_exception)</code>.</p><p><code>_julia_init()</code> then returns <a href="https://github.com/JuliaLang/julia/blob/master/ui/repl.c">back to <code>main()</code> in <code>ui/repl.c</code></a> and <code>main()</code> calls <code>true_main(argc, (char**)argv)</code>.</p><div class="admonition sidebar"><div class="admonition-title">sysimg</div><div class="admonition-text"><p>If there is a sysimg file, it contains a pre-cooked image of the <code>Core</code> and <code>Main</code> modules (and whatever else is created by <code>boot.jl</code>). See <a href="sysimg.html#Building-the-Julia-system-image-1">Building the Julia system image</a>.</p><p><a href="https://github.com/JuliaLang/julia/blob/master/src/dump.c"><code>jl_restore_system_image()</code></a> deserializes the saved sysimg into the current Julia runtime environment and initialization continues after <code>jl_init_box_caches()</code> below...</p><p>Note: <a href="https://github.com/JuliaLang/julia/blob/master/src/dump.c"><code>jl_restore_system_image()</code> (and <code>dump.c</code> in general)</a> uses the <a href="stdio.html#Legacy-ios.c-library-1">Legacy <code>ios.c</code> library</a>.</p></div></div><h2><a class="nav-anchor" id="true_main()-1" href="#true_main()-1">true_main()</a></h2><p><a href="https://github.com/JuliaLang/julia/blob/master/ui/repl.c"><code>true_main()</code></a> loads the contents of <code>argv[]</code> into <a href="../stdlib/constants.html#Base.ARGS"><code>Base.ARGS</code></a>.</p><p>If a <code>.jl</code> "program" file was supplied on the command line, then <a href="https://github.com/JuliaLang/julia/blob/master/ui/repl.c"><code>exec_program()</code></a> calls <a href="https://github.com/JuliaLang/julia/blob/master/src/toplevel.c"><code>jl_load(program,len)</code></a> which calls <a href="https://github.com/JuliaLang/julia/blob/master/src/ast.c"><code>jl_parse_eval_all</code></a> which repeatedly calls <a href="https://github.com/JuliaLang/julia/blob/master/src/toplevel.c"><code>jl_toplevel_eval_flex()</code></a> to execute the program.</p><p>However, in our example (<code>julia -e 'println("Hello World!")'</code>), <a href="https://github.com/JuliaLang/julia/blob/master/src/module.c"><code>jl_get_global(jl_base_module, jl_symbol("_start"))</code></a> looks up <a href="https://github.com/JuliaLang/julia/blob/master/base/client.jl"><code>Base._start</code></a> and <a href="https://github.com/JuliaLang/julia/blob/master/src/julia.h"><code>jl_apply()</code></a> executes it.</p><h2><a class="nav-anchor" id="Base._start-1" href="#Base._start-1">Base._start</a></h2><p><a href="https://github.com/JuliaLang/julia/blob/master/base/client.jl"><code>Base._start</code></a> calls <a href="https://github.com/JuliaLang/julia/blob/master/base/client.jl"><code>Base.process_options</code></a> which calls <a href="https://github.com/JuliaLang/julia/blob/master/src/ast.c"><code>jl_parse_input_line("println("Hello World!")")</code></a> to create an expression object and <a href="../stdlib/base.html#Core.eval"><code>Base.eval()</code></a> to execute it.</p><h2><a class="nav-anchor" id="Base.eval-1" href="#Base.eval-1">Base.eval</a></h2><p><a href="../stdlib/base.html#Core.eval"><code>Base.eval()</code></a> was <a href="https://github.com/JuliaLang/julia/blob/master/src/builtins.c">mapped to <code>jl_f_top_eval</code></a> by <code>jl_init_primitives()</code>.</p><p><a href="https://github.com/JuliaLang/julia/blob/master/src/builtins.c"><code>jl_f_top_eval()</code></a> calls <a href="https://github.com/JuliaLang/julia/blob/master/src/builtins.c"><code>jl_toplevel_eval_in(jl_main_module, ex)</code></a>, where <code>ex</code> is the parsed expression <code>println("Hello World!")</code>.</p><p><a href="https://github.com/JuliaLang/julia/blob/master/src/builtins.c"><code>jl_toplevel_eval_in()</code></a> calls <a href="https://github.com/JuliaLang/julia/blob/master/src/toplevel.c"><code>jl_toplevel_eval_flex()</code></a> which calls <a href="https://github.com/JuliaLang/julia/blob/master/src/interpreter.c"><code>eval()</code> in <code>interpreter.c</code></a>.</p><p>The stack dump below shows how the interpreter works its way through various methods of <a href="../stdlib/io-network.html#Base.println"><code>Base.println()</code></a> and <a href="../stdlib/io-network.html#Base.print"><code>Base.print()</code></a> before arriving at <a href="https://github.com/JuliaLang/julia/blob/master/base/stream.jl"><code>write(s::IO, a::Array{T}) where T</code></a> which does <code>ccall(jl_uv_write())</code>.</p><p><a href="https://github.com/JuliaLang/julia/blob/master/src/jl_uv.c"><code>jl_uv_write()</code></a> calls <code>uv_write()</code> to write "Hello World!" to <code>JL_STDOUT</code>. See <a href="stdio.html#Libuv-wrappers-for-stdio-1">Libuv wrappers for stdio</a>.:</p><pre><code class="language-none">Hello World!</code></pre><table><tr><th>Stack frame</th><th>Source code</th><th>Notes</th></tr><tr><td><code>jl_uv_write()</code></td><td><code>jl_uv.c</code></td><td>called though <a href="../stdlib/c.html#ccall"><code>ccall</code></a></td></tr><tr><td><code>julia_write_282942</code></td><td><code>stream.jl</code></td><td>function <code>write!(s::IO, a::Array{T}) where T</code></td></tr><tr><td><code>julia_print_284639</code></td><td><code>ascii.jl</code></td><td><code>print(io::IO, s::String) = (write(io, s); nothing)</code></td></tr><tr><td><code>jlcall_print_284639</code></td><td> </td><td> </td></tr><tr><td><code>jl_apply()</code></td><td><code>julia.h</code></td><td> </td></tr><tr><td><code>jl_trampoline()</code></td><td><code>builtins.c</code></td><td> </td></tr><tr><td><code>jl_apply()</code></td><td><code>julia.h</code></td><td> </td></tr><tr><td><code>jl_apply_generic()</code></td><td><code>gf.c</code></td><td><code>Base.print(Base.TTY, String)</code></td></tr><tr><td><code>jl_apply()</code></td><td><code>julia.h</code></td><td> </td></tr><tr><td><code>jl_trampoline()</code></td><td><code>builtins.c</code></td><td> </td></tr><tr><td><code>jl_apply()</code></td><td><code>julia.h</code></td><td> </td></tr><tr><td><code>jl_apply_generic()</code></td><td><code>gf.c</code></td><td><code>Base.print(Base.TTY, String, Char, Char...)</code></td></tr><tr><td><code>jl_apply()</code></td><td><code>julia.h</code></td><td> </td></tr><tr><td><code>jl_f_apply()</code></td><td><code>builtins.c</code></td><td> </td></tr><tr><td><code>jl_apply()</code></td><td><code>julia.h</code></td><td> </td></tr><tr><td><code>jl_trampoline()</code></td><td><code>builtins.c</code></td><td> </td></tr><tr><td><code>jl_apply()</code></td><td><code>julia.h</code></td><td> </td></tr><tr><td><code>jl_apply_generic()</code></td><td><code>gf.c</code></td><td><code>Base.println(Base.TTY, String, String...)</code></td></tr><tr><td><code>jl_apply()</code></td><td><code>julia.h</code></td><td> </td></tr><tr><td><code>jl_trampoline()</code></td><td><code>builtins.c</code></td><td> </td></tr><tr><td><code>jl_apply()</code></td><td><code>julia.h</code></td><td> </td></tr><tr><td><code>jl_apply_generic()</code></td><td><code>gf.c</code></td><td><code>Base.println(String,)</code></td></tr><tr><td><code>jl_apply()</code></td><td><code>julia.h</code></td><td> </td></tr><tr><td><code>do_call()</code></td><td><code>interpreter.c</code></td><td> </td></tr><tr><td><code>eval()</code></td><td><code>interpreter.c</code></td><td> </td></tr><tr><td><code>jl_interpret_toplevel_expr()</code></td><td><code>interpreter.c</code></td><td> </td></tr><tr><td><code>jl_toplevel_eval_flex()</code></td><td><code>toplevel.c</code></td><td> </td></tr><tr><td><code>jl_toplevel_eval()</code></td><td><code>toplevel.c</code></td><td> </td></tr><tr><td><code>jl_toplevel_eval_in()</code></td><td><code>builtins.c</code></td><td> </td></tr><tr><td><code>jl_f_top_eval()</code></td><td><code>builtins.c</code></td><td> </td></tr></table><p>Since our example has just one function call, which has done its job of printing "Hello World!", the stack now rapidly unwinds back to <code>main()</code>.</p><h2><a class="nav-anchor" id="jl_atexit_hook()-1" href="#jl_atexit_hook()-1">jl_atexit_hook()</a></h2><p><code>main()</code> calls <a href="https://github.com/JuliaLang/julia/blob/master/src/init.c"><code>jl_atexit_hook()</code></a>. This calls <code>_atexit</code> for each module, then calls <a href="https://github.com/JuliaLang/julia/blob/master/src/gc.c"><code>jl_gc_run_all_finalizers()</code></a> and cleans up libuv handles.</p><h2><a class="nav-anchor" id="julia_save()-1" href="#julia_save()-1">julia_save()</a></h2><p>Finally, <code>main()</code> calls <a href="https://github.com/JuliaLang/julia/blob/master/src/init.c"><code>julia_save()</code></a>, which if requested on the command line, saves the runtime state to a new system image. See <a href="https://github.com/JuliaLang/julia/blob/master/src/gf.c"><code>jl_compile_all()</code></a> and <a href="https://github.com/JuliaLang/julia/blob/master/src/dump.c"><code>jl_save_system_image()</code></a>.</p><footer><hr/><a class="previous" href="reflection.html"><span class="direction">Previous</span><span class="title">Reflection and introspection</span></a><a class="next" href="ast.html"><span class="direction">Next</span><span class="title">Julia ASTs</span></a></footer></article></body></html>
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