iOS Technology interview 02: memory management

<span id="Label3"></p> <ol> <ol> <li>How to ensure that many people develop a memory leak check <span style="font-family: Cambria;">.</span> How do I locate a memory leak?</li> </ol> </ol><p class="p15"><p class="p15">1> <span style="font-family: Cambria;"></span> <span style="font-family: 宋体;">Static analysis of code using ANALYZE (detects potential memory Leaks)</span></p></p><p class="p15"><p class="p15">2> through <span style="font-family: Cambria;">leak</span> <span style="font-family: 宋体;">check for memory leaks during program run</span></p></p><p class="p15"><p class="p15">3> in order to avoid unnecessary trouble <span style="font-family: Cambria;">,</span> <span style="font-family: 宋体;">multi-person development when possible to use</span> <span style="font-family: Cambria;">ARC</span></p></p><p class="p15"><p class="p15"></p></p><p class="p0"><p class="p0">2<span style="font-family: 宋体;">. How to do the singleton mode in the case of non-automatic memory management</span> <span style="font-family: Cambria;">.</span></p></p><p class="p0"><p class="p0">Basic steps to create a singleton design pattern ·</p></p><p class="p0"><p class="p0">> <span style="font-family: 宋体;">declares a static instance of a single object</span> <span style="font-family: 宋体;">and initializes</span> <span style="font-family: Cambria;">it to</span> <span style="font-family: Cambria;">nil</span><span style="font-family: 宋体;">. </span></p></p><p class="p0"><p class="p0">> <span style="font-family: 宋体;">Create a class factory method</span> <span style="font-family: Cambria;">that</span> <span style="font-family: 宋体;">generates an instance of a</span> class if <span style="font-family: 宋体;">and only if the instance of the class is</span> <span style="font-family: Cambria;">nil</span></p></p><p class="p0"><p class="p0">><span style="font-family: arial;"> implement </span> <span style="font-family:cambria;">nscopying </span> <span style="font-family: Song body;" "> protocol </span> <span style="font-family:cambria;">,  </span> <span style="font-family: song body;"> overwrite </span> <span style="font-family:cambria;">allocwithzone: </span> <span style="font-family: The song body;"> method </span> <span style="font-family:cambria;" , < span> <span style="font-family: The song body;"> Ensure that users are assigned and initializing objects directly </span> <span style="font-family:cambria;" , < span> <span style="font-family: The song body;"> Not another object will be produced  .   </span> </span></span></p></p><p class="p0"><p class="p0">> <span style="font-family: 宋体;">cover</span> <span style="font-family: Cambria;">release</span><span style="font-family: 宋体;">,</span><span style="font-family: Cambria;">autorelease</span><span style="font-family: 宋体;">,</span><span style="font-family: Cambria;">retain</span><span style="font-family: 宋体;">,</span> <span style="font-family: Cambria;"> The Retaincount</span> <span style="font-family: 宋体;">method</span> <span style="font-family: Cambria;">is</span> used <span style="font-family: 宋体;">to ensure the status of the Singleton. </span></p></p><p class="p0"><p class="p0">> <span style="font-family: 宋体;">in a multithreaded environment</span> <span style="font-family: Cambria;">,</span> <span style="font-family: 宋体;">Note the use</span> <span style="font-family: Cambria;">of @synchronized</span> <span style="font-family: 宋体;">keywords or</span> <span style="font-family: Cambria;">GCD,</span> <span style="font-family: 宋体;"> Make sure that the static instance is created and initialized correctly. </span></p></p><p class="p0"><p class="p0"></p></p><p class="p0"><p class="p0">3<span style="font-family: 宋体;">. The default for class methods (static Methods) is</span> <span style="font-family: Cambria;">autorelease</span> <span style="font-family: 宋体;">. Will all class methods be like this? </span></p></p><p class="p0"><p class="p0">The 1> <span style="font-family: 宋体;">system comes with a large number of methods that return objects</span> <span style="font-family: Cambria;">,</span> <span style="font-family: 宋体;">all</span> of which are autorelease</p></p><p class="p0"><p class="p0"></p></p><p class="p0"><p class="p0">4<span style="font-family: 宋体;">. </span> <span style="font-family: 宋体;">What is the difference between the usage</span> of <span style="font-family: Cambria;">block</span> <span style="font-family: 宋体;">in</span> <span style="font-family: Cambria;">ARC</span> <span style="font-family: 宋体;"></span> and <span style="font-family: Cambria;">MRC</span> <span style="font-family: Cambria;">,</span> <span style="font-family: 宋体;"> What to pay attention to</span></p></p><p class="p0"><p class="p0">1. <span style="font-family: 宋体;">either</span> <span style="font-family: Cambria;">ARC</span> <span style="font-family: 宋体;">or</span> <span style="font-family: Cambria;">MRC</span><span style="font-family: 宋体;">, the</span><span style="font-family: Cambria;">block</span> <span style="font-family: 宋体;">should be held with</span> a <span style="font-family: Cambria;">copy</span> <span style="font-family: 宋体;">operation </span></p></p><p class="p0"><p class="p0"></p></p> <ol> <ol> <li>Care should be taken to avoid circular references</li> </ol> </ol><p class="p15"><p class="p15">1> ARC: __weak<span style="font-family: 宋体;">,</span><span style="font-family: Cambria;">__unscafe_unretained</span></p></p><p class="p15"><p class="p15">2> Mrc:__block</p></p><p class="p0"><p class="p0"></p></p><p class="p0"><p class="p0">5<span style="font-family: 宋体;">. </span>under what circumstances will a memory leak and memory overflow occur?</p></p><p class="p0"><p class="p0">1> <span style="font-family: 宋体;">Memory Leak: The release is not Released. Memory leaks accumulate a serious consequence, no matter how much memory</span> <span style="font-family: Arial;">,</span> <span style="font-family: 宋体;">sooner or later, will be occupied by light. Memory leaks will eventually cause memory overflow! </span></p></p><p class="p0"><p class="p0">2> <span style="font-family: 宋体;">Memory Overflow: full memory, not enough</span></p></p><p class="p0"><p class="p0">When the program is applying for memory, there is not enough memory space for it to use, and <span style="font-family: Arial;"></span><span style="font-family: 宋体;">an out</span> of memories appears; For example <span style="font-family: Arial;">, an int</span> was applied, <span style="font-family: 宋体;">but it was saved</span> <span style="font-family: Arial;">long</span> <span style="font-family: 宋体;"> To save the number, that is the memory overflow. </span></p></p><p class="p0"><p class="p0"></p></p><p class="p0"><p class="p0">6<span style="font-family: 宋体;">. </span>[nsarray arraywithobject:<id>] Does this method need to be freed after adding an object?</p></p><p class="p0"><p class="p0">This object is not required to be placed in the Auto-release pool</p></p><p class="p0"><p class="p0"></p></p><p class="p0"><p class="p0">7<span style="font-family: 宋体;">. </span> <span style="font-family: Cambria;"></span> <span style="font-family: 宋体;">is there a memory leak when parsing the Json data and parsing the data? Some words how to solve</span></p></p><p class="p15"><p class="p15">1> JSON <span style="font-family: 宋体;">Parsing scheme</span></p></p><p class="p15"><p class="p15">L Sbjson</p></p><p class="p15"><p class="p15">L Jsonkit</p></p><p class="p15"><p class="p15">L Nsjsonserialization</p></p><p class="p0"><p class="p0"></p></p><p class="p15"><p class="p15">2> memory leaks <span style="font-family: Cambria;">?</span></p></p><p class="p0"><p class="p0"></p></p><p class="p0"><p class="p0">8. <span style="font-family: 宋体;">Automatic release of the pool bottom how to implement</span></p></p><p class="p0"><p class="p0">The Auto-free pool is implemented as a stack <span style="font-family: Cambria;">:</span> when <span style="font-family: 宋体;">you create a new Auto-free pool, it is added to the top of the Stack. When an object receives a send</span> <span style="font-family: Cambria;">autorelease</span> <span style="font-family: 宋体;">message</span> <span style="font-family: Cambria;">,</span> <span style="font-family: 宋体;">It is added to the current Thread's top-of-stack auto-release pool</span> <span style="font-family: Cambria;">,</span> when the <span style="font-family: 宋体;">auto-free pool is recycled </span> <span style="font-family: Cambria;">,</span> <span style="font-family: 宋体;">They are removed from the stack</span> <span style="font-family: Cambria;">,</span> <span style="font-family: 宋体;">and all objects inside the pool are given a</span> <span style="font-family: Cambria;">release</span> <span style="font-family: 宋体;">operation</span> <span style="font-family: Cambria;">.</span></p></p><p class="p0"><p class="p0">9 <span style="font-family: 宋体;">Increase</span> The <span style="font-family: 宋体;">memory consumption behavior of</span> an <span style="font-family: Cambria;">APP</span> :</p></p><p class="p0"><p class="p0">Create an OC <span style="font-family: 宋体;">object;</span></p></p><p class="p0"><p class="p0">Define a variable;</p></p><p class="p0"><p class="p0">Call a function or method</p></p><p class="p0"><p class="p0">Memory is too large, the system may force the <span style="font-family: Cambria;">APP</span>to close<span style="font-family: 宋体;">. The phenomenon of Flash-back is</span> that the <span style="font-family: Cambria;">APP</span> <span style="font-family: 宋体;">suddenly crashes and exits meaning, affecting the user experience. </span></p></p><p class="p0"><p class="p0">Only OC <span style="font-family: 宋体;">objects require the essential reasons for memory Management:</span></p></p><p class="p0"><p class="p0">OC <span style="font-family: 宋体;">objects stored in the heap, non-</span> <span style="font-family: Cambria;">oc</span> <span style="font-family: 宋体;">objects are generally placed inside the stack, the system will automatically recycle stack memory</span></p></p><p><p>iOS Technology interview 02: memory management</p></p></span>