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</pre><div class="example-wrap"><pre class="rust ">
<span class="attribute">#![<span class="ident">cfg</span>(<span class="ident">target_thread_local</span>)]</span>
<span class="attribute">#![<span class="ident">unstable</span>(<span class="ident">feature</span> <span class="op">=</span> <span class="string">&quot;thread_local_internals&quot;</span>, <span class="ident">issue</span> <span class="op">=</span> <span class="string">&quot;0&quot;</span>)]</span>

<span class="comment">// Since what appears to be glibc 2.18 this symbol has been shipped which</span>
<span class="comment">// GCC and clang both use to invoke destructors in thread_local globals, so</span>
<span class="comment">// let&#39;s do the same!</span>
<span class="comment">//</span>
<span class="comment">// Note, however, that we run on lots older linuxes, as well as cross</span>
<span class="comment">// compiling from a newer linux to an older linux, so we also have a</span>
<span class="comment">// fallback implementation to use as well.</span>
<span class="comment">//</span>
<span class="comment">// Due to rust-lang/rust#18804, make sure this is not generic!</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">any</span>(<span class="ident">target_os</span> <span class="op">=</span> <span class="string">&quot;linux&quot;</span>, <span class="ident">target_os</span> <span class="op">=</span> <span class="string">&quot;fuchsia&quot;</span>, <span class="ident">target_os</span> <span class="op">=</span> <span class="string">&quot;hermit&quot;</span>))]</span>
<span class="kw">pub</span> <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">register_dtor</span>(<span class="ident">t</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>, <span class="ident">dtor</span>: <span class="kw">unsafe</span> <span class="kw">extern</span> <span class="kw">fn</span>(<span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>)) {
    <span class="kw">use</span> <span class="kw">crate</span>::<span class="ident">mem</span>;
    <span class="kw">use</span> <span class="kw">crate</span>::<span class="ident">sys_common</span>::<span class="ident">thread_local</span>::<span class="ident">register_dtor_fallback</span>;

    <span class="kw">extern</span> {
        <span class="attribute">#[<span class="ident">linkage</span> <span class="op">=</span> <span class="string">&quot;extern_weak&quot;</span>]</span>
        <span class="kw">static</span> <span class="ident">__dso_handle</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>;
        <span class="attribute">#[<span class="ident">linkage</span> <span class="op">=</span> <span class="string">&quot;extern_weak&quot;</span>]</span>
        <span class="kw">static</span> <span class="ident">__cxa_thread_atexit_impl</span>: <span class="kw-2">*</span><span class="kw">const</span> <span class="ident">libc</span>::<span class="ident">c_void</span>;
    }
    <span class="kw">if</span> <span class="op">!</span><span class="ident">__cxa_thread_atexit_impl</span>.<span class="ident">is_null</span>() {
        <span class="kw">type</span> <span class="ident">F</span> <span class="op">=</span> <span class="kw">unsafe</span> <span class="kw">extern</span> <span class="kw">fn</span>(<span class="ident">dtor</span>: <span class="kw">unsafe</span> <span class="kw">extern</span> <span class="kw">fn</span>(<span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>),
                                  <span class="ident">arg</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>,
                                  <span class="ident">dso_handle</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>) <span class="op">-&gt;</span> <span class="ident">libc</span>::<span class="ident">c_int</span>;
        <span class="ident">mem</span>::<span class="ident">transmute</span>::<span class="op">&lt;</span><span class="kw-2">*</span><span class="kw">const</span> <span class="ident">libc</span>::<span class="ident">c_void</span>, <span class="ident">F</span><span class="op">&gt;</span>(<span class="ident">__cxa_thread_atexit_impl</span>)
            (<span class="ident">dtor</span>, <span class="ident">t</span>, <span class="kw-2">&amp;</span><span class="ident">__dso_handle</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw">const</span> <span class="kw">_</span> <span class="kw">as</span> <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="kw">_</span>);
        <span class="kw">return</span>
    }
    <span class="ident">register_dtor_fallback</span>(<span class="ident">t</span>, <span class="ident">dtor</span>);
}

<span class="comment">// This implementation is very similar to register_dtor_fallback in</span>
<span class="comment">// sys_common/thread_local.rs. The main difference is that we want to hook into</span>
<span class="comment">// macOS&#39;s analog of the above linux function, _tlv_atexit. OSX will run the</span>
<span class="comment">// registered dtors before any TLS slots get freed, and when the main thread</span>
<span class="comment">// exits.</span>
<span class="comment">//</span>
<span class="comment">// Unfortunately, calling _tlv_atexit while tls dtors are running is UB. The</span>
<span class="comment">// workaround below is to register, via _tlv_atexit, a custom DTOR list once per</span>
<span class="comment">// thread. thread_local dtors are pushed to the DTOR list without calling</span>
<span class="comment">// _tlv_atexit.</span>
<span class="attribute">#[<span class="ident">cfg</span>(<span class="ident">target_os</span> <span class="op">=</span> <span class="string">&quot;macos&quot;</span>)]</span>
<span class="kw">pub</span> <span class="kw">unsafe</span> <span class="kw">fn</span> <span class="ident">register_dtor</span>(<span class="ident">t</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>, <span class="ident">dtor</span>: <span class="kw">unsafe</span> <span class="kw">extern</span> <span class="kw">fn</span>(<span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>)) {
    <span class="kw">use</span> <span class="kw">crate</span>::<span class="ident">cell</span>::<span class="ident">Cell</span>;
    <span class="kw">use</span> <span class="kw">crate</span>::<span class="ident">ptr</span>;

    <span class="attribute">#[<span class="ident">thread_local</span>]</span>
    <span class="kw">static</span> <span class="ident">REGISTERED</span>: <span class="ident">Cell</span><span class="op">&lt;</span><span class="ident">bool</span><span class="op">&gt;</span> <span class="op">=</span> <span class="ident">Cell</span>::<span class="ident">new</span>(<span class="bool-val">false</span>);
    <span class="kw">if</span> <span class="op">!</span><span class="ident">REGISTERED</span>.<span class="ident">get</span>() {
        <span class="ident">_tlv_atexit</span>(<span class="ident">run_dtors</span>, <span class="ident">ptr</span>::<span class="ident">null_mut</span>());
        <span class="ident">REGISTERED</span>.<span class="ident">set</span>(<span class="bool-val">true</span>);
    }

    <span class="kw">type</span> <span class="ident">List</span> <span class="op">=</span> <span class="ident">Vec</span><span class="op">&lt;</span>(<span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>, <span class="kw">unsafe</span> <span class="kw">extern</span> <span class="kw">fn</span>(<span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>))<span class="op">&gt;</span>;

    <span class="attribute">#[<span class="ident">thread_local</span>]</span>
    <span class="kw">static</span> <span class="ident">DTORS</span>: <span class="ident">Cell</span><span class="op">&lt;</span><span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">List</span><span class="op">&gt;</span> <span class="op">=</span> <span class="ident">Cell</span>::<span class="ident">new</span>(<span class="ident">ptr</span>::<span class="ident">null_mut</span>());
    <span class="kw">if</span> <span class="ident">DTORS</span>.<span class="ident">get</span>().<span class="ident">is_null</span>() {
        <span class="kw">let</span> <span class="ident">v</span>: <span class="ident">Box</span><span class="op">&lt;</span><span class="ident">List</span><span class="op">&gt;</span> <span class="op">=</span> <span class="kw">box</span> <span class="ident">Vec</span>::<span class="ident">new</span>();
        <span class="ident">DTORS</span>.<span class="ident">set</span>(<span class="ident">Box</span>::<span class="ident">into_raw</span>(<span class="ident">v</span>));
    }

    <span class="kw">extern</span> {
        <span class="kw">fn</span> <span class="ident">_tlv_atexit</span>(<span class="ident">dtor</span>: <span class="kw">unsafe</span> <span class="kw">extern</span> <span class="kw">fn</span>(<span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>),
                       <span class="ident">arg</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>);
    }

    <span class="kw">let</span> <span class="ident">list</span>: <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="ident">List</span> <span class="op">=</span> <span class="kw-2">&amp;</span><span class="kw-2">mut</span> <span class="kw-2">*</span><span class="ident">DTORS</span>.<span class="ident">get</span>();
    <span class="ident">list</span>.<span class="ident">push</span>((<span class="ident">t</span>, <span class="ident">dtor</span>));

    <span class="kw">unsafe</span> <span class="kw">extern</span> <span class="kw">fn</span> <span class="ident">run_dtors</span>(<span class="kw">_</span>: <span class="kw-2">*</span><span class="kw-2">mut</span> <span class="ident">u8</span>) {
        <span class="kw">let</span> <span class="kw-2">mut</span> <span class="ident">ptr</span> <span class="op">=</span> <span class="ident">DTORS</span>.<span class="ident">replace</span>(<span class="ident">ptr</span>::<span class="ident">null_mut</span>());
        <span class="kw">while</span> <span class="op">!</span><span class="ident">ptr</span>.<span class="ident">is_null</span>() {
            <span class="kw">let</span> <span class="ident">list</span> <span class="op">=</span> <span class="ident">Box</span>::<span class="ident">from_raw</span>(<span class="ident">ptr</span>);
            <span class="kw">for</span> (<span class="ident">ptr</span>, <span class="ident">dtor</span>) <span class="kw">in</span> <span class="ident">list</span>.<span class="ident">into_iter</span>() {
                <span class="ident">dtor</span>(<span class="ident">ptr</span>);
            }
            <span class="ident">ptr</span> <span class="op">=</span> <span class="ident">DTORS</span>.<span class="ident">replace</span>(<span class="ident">ptr</span>::<span class="ident">null_mut</span>());
        }
    }
}

<span class="kw">pub</span> <span class="kw">fn</span> <span class="ident">requires_move_before_drop</span>() <span class="op">-&gt;</span> <span class="ident">bool</span> {
    <span class="bool-val">false</span>
}
</pre></div>
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