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<div class="title">Co-routines </div> </div>
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<div class="contents">
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<div class="textblock"><p>Co-routines is a way to allow multiple execution paths in parallel, but without the hazards of pre-emptive scheduling in <a class="el" href="doc_adv_concurrent.html">multithreading</a> where one thread can be suspended at any moment so another can resume. Because co-routines always voluntarily suspend themselves in favor of the next co-routine, there is no need to worry about atomic instructions and critical sections.</p>
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<p>Co-routines are not natively built-into the AngelScript library, but it can easily be implemented from the application side. In fact, the <a class="el" href="doc_addon_ctxmgr.html">Context manager</a> add-on already provides a default implementation for this.</p>
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<p>To implement your own version of co-routines you will need a couple of pieces:</p>
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<ul>
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<li>The co-routine itself, which is just an instance of the <a class="el" href="classas_i_script_context.html">asIScriptContext</a> object. Each co-routine will have its own context object that holds the callstack of the co-routine.</li>
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<li>A function that will permit the script to create, or spawn, new co-routines. This function will need to be able to refer to starting function of the new co-routine. This reference can be done by name, or perhaps more elegantly with a <a class="el" href="doc_datatypes_funcptr.html">function pointer</a>. Once invoked this function will instanciate the new context, and prepare it with the starting function.</li>
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<li>A function that will permit a co-routine to yield control to the next co-routine. This function will simply suspend the current context so the next co-routine can be resumed.</li>
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<li>A simple control algorithm for the co-routines. This can just be a loop that will iterate over an array of co-routines, i.e. contexts, until all of them have finished executing. When a new co-routine is created it is simply appended to the array to be picked up when the current co-routine yields the control.</li>
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</ul>
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<p>A simple implementation of the function that spawns a new co-routine may look like this:</p>
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<div class="fragment"><div class="line"><span class="keywordtype">void</span> CreateCoRoutine(<span class="keywordtype">string</span> &func)</div>
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<div class="line">{</div>
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<div class="line"> <a class="code" href="classas_i_script_context.html">asIScriptContext</a> *ctx = <a class="code" href="group__api__principal__functions.html#gad3a20dc58093b92a5a44c7b6ada34a10">asGetActiveContext</a>();</div>
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<div class="line"> <span class="keywordflow">if</span>( ctx )</div>
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<div class="line"> {</div>
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<div class="line"> <a class="code" href="classas_i_script_engine.html">asIScriptEngine</a> *engine = ctx-><a class="code" href="classas_i_script_context.html#a07f12016c5435aec5b63449abb6e4d8d">GetEngine</a>();</div>
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<div class="line"> <span class="keywordtype">string</span> mod = ctx-><a class="code" href="classas_i_script_context.html#a1c101300447f2909e5d188409a7180f6">GetFunction</a>()-><a class="code" href="classas_i_script_function.html#af03c30e4764f81c01400d7f77a8d0832">GetModuleName</a>();</div>
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<div class="line"> </div>
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<div class="line"> <span class="comment">// We need to find the function that will be created as the co-routine</span></div>
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<div class="line"> <span class="keywordtype">string</span> decl = <span class="stringliteral">"void "</span> + func + <span class="stringliteral">"()"</span>; </div>
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<div class="line"> <a class="code" href="classas_i_script_function.html">asIScriptFunction</a> *funcPtr = engine-><a class="code" href="classas_i_script_engine.html#a9f7cdc52b59034e6e55eb8a56b427aa4">GetModule</a>(mod.c_str())-><a class="code" href="classas_i_script_module.html#ab4754d55d8667aefbed135b4794d461b">GetFunctionByDecl</a>(decl.c_str());</div>
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<div class="line"> <span class="keywordflow">if</span>( funcPtr == 0 )</div>
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<div class="line"> {</div>
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<div class="line"> <span class="comment">// No function could be found, raise an exception</span></div>
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<div class="line"> ctx-><a class="code" href="classas_i_script_context.html#a6f0f071215e0f7effc0b765043f01275">SetException</a>((<span class="stringliteral">"Function '"</span> + decl + <span class="stringliteral">"' doesn't exist"</span>).c_str());</div>
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<div class="line"> <span class="keywordflow">return</span>;</div>
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<div class="line"> }</div>
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<div class="line"> </div>
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<div class="line"> <span class="comment">// Create a new context for the co-routine</span></div>
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<div class="line"> <a class="code" href="classas_i_script_context.html">asIScriptContext</a> *coctx = engine-><a class="code" href="classas_i_script_engine.html#a2630e1cd03ffab0fee9b820bf0afe42a">CreateContext</a>();</div>
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<div class="line"> coctx-><a class="code" href="classas_i_script_context.html#a43976f42dfc6c1af23e132d36265173a">Prepare</a>(funcPtr);</div>
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<div class="line"> </div>
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<div class="line"> <span class="comment">// Add the new co-routine context to the array of co-routines</span></div>
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<div class="line"> coroutines.push_back(coctx);</div>
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<div class="line"> }</div>
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<div class="line">}</div>
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</div><!-- fragment --><p>The yield function is even simpler:</p>
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<div class="fragment"><div class="line"><span class="keywordtype">void</span> Yield()</div>
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<div class="line">{</div>
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<div class="line"> <a class="code" href="classas_i_script_context.html">asIScriptContext</a> *ctx = <a class="code" href="group__api__principal__functions.html#gad3a20dc58093b92a5a44c7b6ada34a10">asGetActiveContext</a>();</div>
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<div class="line"> <span class="keywordflow">if</span>( ctx )</div>
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<div class="line"> { </div>
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<div class="line"> <span class="comment">// Suspend the context so the next co-routine can be resumed</span></div>
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<div class="line"> ctx-><a class="code" href="classas_i_script_context.html#ad4ac8be3586c46069b5870e40c86544a">Suspend</a>();</div>
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<div class="line"> }</div>
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<div class="line">}</div>
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</div><!-- fragment --><p>A basic control algorithm might look like this:</p>
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<div class="fragment"><div class="line">std::vector<asIScriptContext *> coroutines;</div>
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<div class="line"><span class="keywordtype">void</span> Execute()</div>
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<div class="line">{</div>
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<div class="line"> <span class="keywordtype">int</span> n = 0;</div>
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<div class="line"> <span class="keywordflow">while</span>( coroutines.size() > 0 )</div>
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<div class="line"> {</div>
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<div class="line"> <span class="comment">// Resume the co-routine</span></div>
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<div class="line"> <span class="keywordtype">int</span> r = coroutines[n]->Execute();</div>
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<div class="line"> <span class="keywordflow">if</span>( r == <a class="code" href="angelscript_8h.html#a867f14b4137dd4602fda1e616b217a69a7b5644be315c46f2fa44f032731242c7">asEXECUTION_SUSPENDED</a> )</div>
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<div class="line"> {</div>
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<div class="line"> <span class="comment">// Resume the next co-routine</span></div>
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<div class="line"> <span class="keywordflow">if</span>( ++n == coroutines.size() )</div>
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<div class="line"> n = 0;</div>
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<div class="line"> }</div>
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<div class="line"> <span class="keywordflow">else</span></div>
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<div class="line"> {</div>
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<div class="line"> <span class="comment">// The co-routine finished so let's remove it</span></div>
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<div class="line"> coroutines[n]->Release();</div>
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<div class="line"> coroutines.erase(n);</div>
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<div class="line"> }</div>
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<div class="line"> }</div>
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<div class="line">}</div>
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</div><!-- fragment --><dl class="section see"><dt>See also</dt><dd><a class="el" href="doc_addon_ctxmgr.html">Context manager</a>, <a class="el" href="doc_samples_corout.html">Co-routines</a>, <a class="el" href="doc_adv_concurrent.html">Concurrent scripts</a> </dd></dl>
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</div></div><!-- contents -->
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</div><!-- PageDoc -->
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</div><!-- doc-content -->
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<div class="ttc" id="aclassas_i_script_context_html"><div class="ttname"><a href="classas_i_script_context.html">asIScriptContext</a></div><div class="ttdoc">The interface to the virtual machine.</div><div class="ttdef"><b>Definition:</b> angelscript.h:2717</div></div>
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<div class="ttc" id="aclassas_i_script_context_html_a1c101300447f2909e5d188409a7180f6"><div class="ttname"><a href="classas_i_script_context.html#a1c101300447f2909e5d188409a7180f6">asIScriptContext::GetFunction</a></div><div class="ttdeci">virtual asIScriptFunction * GetFunction(asUINT stackLevel=0)=0</div><div class="ttdoc">Returns the function at the specified callstack level.</div></div>
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<div class="ttc" id="aangelscript_8h_html_a867f14b4137dd4602fda1e616b217a69a7b5644be315c46f2fa44f032731242c7"><div class="ttname"><a href="angelscript_8h.html#a867f14b4137dd4602fda1e616b217a69a7b5644be315c46f2fa44f032731242c7">asEXECUTION_SUSPENDED</a></div><div class="ttdeci">@ asEXECUTION_SUSPENDED</div><div class="ttdoc">The execution is suspended and can be resumed.</div><div class="ttdef"><b>Definition:</b> angelscript.h:400</div></div>
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<div class="ttc" id="aclassas_i_script_module_html_ab4754d55d8667aefbed135b4794d461b"><div class="ttname"><a href="classas_i_script_module.html#ab4754d55d8667aefbed135b4794d461b">asIScriptModule::GetFunctionByDecl</a></div><div class="ttdeci">virtual asIScriptFunction * GetFunctionByDecl(const char *decl) const =0</div><div class="ttdoc">Returns the function by its declaration.</div></div>
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<div class="ttc" id="aclassas_i_script_engine_html_a9f7cdc52b59034e6e55eb8a56b427aa4"><div class="ttname"><a href="classas_i_script_engine.html#a9f7cdc52b59034e6e55eb8a56b427aa4">asIScriptEngine::GetModule</a></div><div class="ttdeci">virtual asIScriptModule * GetModule(const char *module, asEGMFlags flag=asGM_ONLY_IF_EXISTS)=0</div><div class="ttdoc">Return an interface pointer to the module.</div></div>
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<div class="ttc" id="aclassas_i_script_engine_html"><div class="ttname"><a href="classas_i_script_engine.html">asIScriptEngine</a></div><div class="ttdoc">The engine interface.</div><div class="ttdef"><b>Definition:</b> angelscript.h:1092</div></div>
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<div class="ttc" id="aclassas_i_script_function_html_af03c30e4764f81c01400d7f77a8d0832"><div class="ttname"><a href="classas_i_script_function.html#af03c30e4764f81c01400d7f77a8d0832">asIScriptFunction::GetModuleName</a></div><div class="ttdeci">virtual const char * GetModuleName() const =0</div><div class="ttdoc">Returns the name of the module where the function was implemented.</div></div>
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<div class="ttc" id="aclassas_i_script_context_html_a07f12016c5435aec5b63449abb6e4d8d"><div class="ttname"><a href="classas_i_script_context.html#a07f12016c5435aec5b63449abb6e4d8d">asIScriptContext::GetEngine</a></div><div class="ttdeci">virtual asIScriptEngine * GetEngine() const =0</div><div class="ttdoc">Returns a pointer to the engine.</div></div>
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<div class="ttc" id="aclassas_i_script_context_html_ad4ac8be3586c46069b5870e40c86544a"><div class="ttname"><a href="classas_i_script_context.html#ad4ac8be3586c46069b5870e40c86544a">asIScriptContext::Suspend</a></div><div class="ttdeci">virtual int Suspend()=0</div><div class="ttdoc">Suspends the execution, which can then be resumed by calling Execute again.</div></div>
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<div class="ttc" id="aclassas_i_script_engine_html_a2630e1cd03ffab0fee9b820bf0afe42a"><div class="ttname"><a href="classas_i_script_engine.html#a2630e1cd03ffab0fee9b820bf0afe42a">asIScriptEngine::CreateContext</a></div><div class="ttdeci">virtual asIScriptContext * CreateContext()=0</div><div class="ttdoc">Creates a new script context.</div></div>
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<div class="ttc" id="aclassas_i_script_function_html"><div class="ttname"><a href="classas_i_script_function.html">asIScriptFunction</a></div><div class="ttdoc">The interface for a script function description.</div><div class="ttdef"><b>Definition:</b> angelscript.h:3823</div></div>
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<div class="ttc" id="aclassas_i_script_context_html_a6f0f071215e0f7effc0b765043f01275"><div class="ttname"><a href="classas_i_script_context.html#a6f0f071215e0f7effc0b765043f01275">asIScriptContext::SetException</a></div><div class="ttdeci">virtual int SetException(const char *info, bool allowCatch=true)=0</div><div class="ttdoc">Sets an exception, which aborts the execution.</div></div>
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<div class="ttc" id="aclassas_i_script_context_html_a43976f42dfc6c1af23e132d36265173a"><div class="ttname"><a href="classas_i_script_context.html#a43976f42dfc6c1af23e132d36265173a">asIScriptContext::Prepare</a></div><div class="ttdeci">virtual int Prepare(asIScriptFunction *func)=0</div><div class="ttdoc">Prepares the context for execution of the function.</div></div>
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<div class="ttc" id="agroup__api__principal__functions_html_gad3a20dc58093b92a5a44c7b6ada34a10"><div class="ttname"><a href="group__api__principal__functions.html#gad3a20dc58093b92a5a44c7b6ada34a10">asGetActiveContext</a></div><div class="ttdeci">AS_API asIScriptContext * asGetActiveContext()</div><div class="ttdoc">Returns the currently active context.</div></div>
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