I am preparing for the OCP exam and I found this question in a mock exam:  Given:  class Calculator {     private AtomicInteger i = new AtomicInteger();     public void add(int value) {         int oldValue = i.get();         int newValue = oldValue + value;         System.out.print(i.compareAndSet(oldValue,newValue));     }     public int getValue() {         return i.get();     } }   What could you do to make this class thread safe?  And surprisingly, to me, the answer is: "Class Calculator is thread-safe"  It must be that I have not understood correctly the concept. To my understanding, a class is thread safe when all the methods work as expected under thread concurrency. Now, if two thread call at the same time getValue(), then call add() passing a different value, and then they call getValue() again, the 'second' thread won't see its value passed increased.  I understand that the oldValue and the newValue as local variables are stored in the method stack, but that doesn't prevent that the second call to compareAndSet will find that the oldValue is not the current value and so won't add the newValue.  What am I missing here?
Does it mean that two threads can't change the underlying data simultaneously? Or does it mean that the given code segment will run with predictable results when multiple threads are executing that code segment?
I'm confused about the use of symbols $\vdash$ and  $ \models$. Reading the answers to  and  I see that:  the turnstile symbol $ \vdash $ denotes syntactic implication. Then $ S \vdash \psi$ means that $\psi$ can be derived from the formulae in $S$  the double turnstile $ \models $, denotes semantic implication. Then the notation $A \models B$ means simply that B is true in every model in which A is true.  So I understand that, e.g., $(ZFC+ A) \vdash B$ means that $A \Rightarrow B$ is a theorem in ZFC and, in this sense $\vdash$ is a mathematical symbol for a theorem. While $(ZFC+ A) \models B$ means that $ B$ is true in every model of ZFC in which $A$ is true, and, in this sense $\models$ is not a mathematical but a metamathematical symbol.  I understand correctly? And those are the only uses of the two symbols? I'm running Bash scripting, but sometimes I get confused which of these commands I use belong to who. Sometimes man xxx works, sometimes doesn't, so I use --help or info, mostly one of these works to show description of the command. Can anyone tell me how I would know what command belongs to what? Bash builtin, GNU utility, etc. Find the sum of two elements in a matrix Given $[a_{ij}]_{10\times10}=\left[ \begin{array}{ccc}   1&amp;2&amp;4&amp;7&amp;...&amp;...&amp;...\\   3&amp;5&amp;8&amp;...&amp;...&amp;...&amp;...\\   6&amp;9&amp;...&amp;...&amp;...&amp;...&amp;...\\   10&amp;...&amp;...&amp;...&amp;...&amp;...&amp;...&amp;\\   ...&amp;...&amp;...&amp;...&amp;...&amp;...&amp;...\\   ...&amp;...&amp;...&amp;...&amp;...&amp;...&amp;98\\   ...&amp;...&amp;...&amp;...&amp;...&amp;99&amp;100\\ \end{array} \right]$, what's $a_{7,3}+a_{7,7}$?  Is there a better way than write down all the elements? It's not easy to find the formula of $a_{i,j}$ Show that $\sum\limits_{n=0}^\infty \frac{z}{(1+z^2)^n}$ converges for all $z\in \mathbb{C}$ outside $|1+z^2|=1$ Show that $\sum\limits_{n=0}^\infty \frac{z}{(1+z^2)^n}$ converges for all $z\in \mathbb{C}$ outside $|1+z^2|=1$  Actually, I have the problem to understand the meaning of "outside $|1+z^2|=1$". If it means that the collection of $z\in\mathbb{C}$ such that $|1+z^2|&gt;1.$ This problem will be easy to verify since for each given $z$ with $|1+z^2|&gt;1$, then we have $|1+z^2|^{-1}&lt;1$. Then, it is the geometric series with common ratio less than $1$ which implies that the series converges.   Do I have correct interpretation with "outside $|1+z^2|=1$"? If not, what is the correct interpretation with this? Thanks. Confused AUC ROC score I am working on binary classification problem, I try to evaluate the performance of some classification algorithms (LR,Decission Tree , Random forest ...). I am using  a cross validation technique (to avoid over-fitting) with AUC ROC as scoring function to compare the performance of the algorithms, but I am getting a weird results with Random forest and AdbBoost, I have a perfect AUC_ROC score (i.e. =1) despite the fact that the recall(TPR) and FPR of this algorithms are different from 1 and 0 respectively .  def FPR(y_true, y_pred):     tn, fp, fn, tp = confusion_matrix(y_true, y_pred).ravel()     result = fp / (fp+tn)     return result def FNR(y_true, y_pred):     tn, fp, fn, tp = confusion_matrix(y_true, y_pred).ravel()     result = fn / (tp+fn)     return result FPR_scorer = make_scorer(FPR) FNR_scorer = make_scorer(FNR)     def get_CrossValResults2(model,cv_rst,bestIndx):     best=pd.DataFrame.from_dict(cv_rst).iloc[bestIndx]     roc=&quot;{:.12f}&quot;.format(best['mean_test_roc_auc'])     acc =&quot;{:.0%}&quot;.format(best['mean_test_accuracy'])     prec =&quot;{:.0%}&quot;.format(best['mean_test_precision'])     rec =&quot;{:.0%}&quot;.format( best['mean_test_recall'])     f1 =&quot;{:.0%}&quot;.format(best['mean_test_f1'])     r2=&quot;{:.2f}&quot;.format(best['mean_test_r2'])     g_mean=&quot;{:.2f}&quot;.format(best['mean_test_gmean'])     pr_auc=&quot;{:.8f}&quot;.format(best['mean_test_pr'])     fnr=&quot;{:.0%}&quot;.format(best['mean_test_fnr'])     fpr=&quot;{:.0%}&quot;.format(best['mean_test_fpr'])     rst = pd.DataFrame([[ model, acc,prec,rec,fpr,fnr,f1,roc,pr_auc,g_mean,r2]],columns = ['Model', 'Accuracy', 'Precision', 'Recall','FPR','FNR', 'F1-Score','ROC_auc','PR_auc','gmean','r2'])     return rst        cross_val_rst = pd.DataFrame(columns = ['Model', 'Accuracy', 'Precision', 'Recall','FPR','FNR', 'F1-Score','ROC_auc','PR_auc','gmean','r2'])              scoring = {'accuracy':'accuracy','recall':'recall','precision':'precision','fpr':FPR_scorer,'fnr':FNR_scorer,'f1':'f1' ,'roc_auc':'roc_auc','pr':'average_precision','gmean':Gmean_scorer,'r2':'r2'}     param_grid = {'n_estimators': [200],               'max_depth': [80,90],               'min_samples_leaf': [2,3, 4],             'min_samples_split': [2,5,12],             'criterion': [ 'gini'],              'class_weight' : [class_weights], 'n_jobs' : [-1]}  clf = GridSearchCV(RandomForestClassifier(class_weight=class_weights), param_grid, cv=kfold,scoring=scoring,refit=refit)#Fit the model bestmodel = clf.fit(X,Y)       cross_val_rst = cross_val_rst.append(get_CrossValResults2(model='Random Forrest',bestIndx=bestmodel.best_index_,cv_rst=bestmodel.cv_results_),ignore_index=True) Remove dots & Page numbers from TOC I am using example given here by @stephan .  Works great however I want to get rid of dots and page numbers.  I added this to the preamble   \let\Contentsline\contentsline  \renewcommand\contentsline[3]{\Contentsline{#1}{#2}{}}   that removed the page numbers, but do not know how to remove the dots. I would appreciate your help. Its hard to get result without understanding the basics. How is it that questions posted to the Stack Overflow show up as #1 in Google search results just minutes after being submitted? What SEO practices are being used to generate this sort of up-to-the-minute accuracy? 3rd iterate of a continuous function equals identity function If $ f: \mathbb{R} \to \mathbb{R} $ is continuous, and $\forall x \in \mathbb{R} :\;(f \circ f \circ f)(x) = x  $, show that $ f(x) = x $.  The condition that $f$ is continuous on $\mathbb{R}$ is crucial for the proof. I can find functions such as $\displaystyle\frac{x-3}{x+1}$ that satisfies  $ (f \circ f \circ f)(x) = x $. I have tried to negate the conclusion to see if there's a contradiction, but got stuck. How do I reset proxy in terminal to automatic if not connected via proxy I tried to reset proxy of the terminal by some commands but it doesn't happen and automatically switches back to this proxy 172.16.0.16 (which apparently was my college proxy).   I checked in my system settings.I don't understand why this is recurring. Please be comprehensive.Also I further would like to know how to bypass proxy server since I couldn't access any of the ubuntu repositories as they were blocked in my college's proxy settings as is Ubuntu's homepage.  Thanks for your time.    For sudo ls /etc/apt/apt.conf.d/        It displays a different set of options where proxy is not listed.I am on 12.10,if this should help any.I put a snap of the terminal after the above command has been entered. I want to create an effect/color like this image of the cloud in the Parse.com logo. It is not quite white, and seems to have a texture. I am new to illustrator, but have a white "cloud" made thanks to some other tutorials. How do I proceed? this works in viewport but not in render.  import bpy from math import *  def frame_handler(scene):     z = scene.objects['Lift'].location[2]     scene.objects['Text'].data.body = str(floor(z / 4.0) - 2)  bpy.app.handlers.frame_change_pre.clear() bpy.app.handlers.frame_change_pre.append(frame_handler)   How to get it working in render? I've read  and changed from "bpy.data.objects" to "scene.objects" as already seen in the script. What am I missing? Blender v. 2.81.16  Edit. Tried that depsgraph thing mentioned in comments and changed to frame_change_post:  import bpy from bpy.app.handlers import persistent from math import *  @persistent  # maybe not relevant but doesn't harm anything? def frame_handler(scene, depsgraph):     z = scene.objects['Lift'].evaluated_get(depsgraph).location[2]     scene.objects['Text'].data.body = str(floor(z / 4.0) - 2)  bpy.app.handlers.frame_change_pre.clear() bpy.app.handlers.frame_change_post.clear() bpy.app.handlers.frame_change_post.append(frame_handler)   Now the Text doesn't show up at all in rendered (but works in viewport). Apache accepting requests to other servers? I'm having problems with apache server (CentOS VPS at Amazon). When apache starts, it starts to receive hundreds of requests, this is an example of the log:  173.208.216.165 - - [25/Jan/2015:18:23:11 +0000] "GET http://go.padstm.com/resources/img/iebt.png HTTP/1.0" 200 36023 "http://go.padstm.com/?id=173374&amp;t=iframe&amp;var=33110" "Mozilla/5.0 (Windows; U; Windows NT 6.1; ru; rv:1.9.2.3) Gecko/20100401 Firefox/4.0 (.NET CLR 3.5.30729)"   The path /resources/img/iebt.png is in my server, but not go.padstm.com. The strangest thing is that apache is accepting all the requests.  Other example: in this case, the entire resource is NOT in my server, but apache returns 200:  198.204.239.250 - - [25/Jan/2015:19:04:39 +0000] "GET http://fstads.com/show.php?z=26&amp;pl=494&amp;j=1&amp;code=1422237874120 HTTP/1.0" 200 10819 "http://financezhen.com/?p=186#respond" "Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:2.2a1pre) Gecko/20110324 Firefox/4.2a1pre"   I don't know why these requests goes to my server, or why it returns 200...  Also, when apache starts and module prefork is enabled, it launches multiple httpd processes. If worker module is enabled, it launches multiple threads. Ok, but in both cases apache ends up consuming all the CPU and memory of the server, and there is not traffic directed to my server.  More info: ProxyRequests is Off. Also: I'm using ip-based vhosts:  NameVirtualHost xxx.xxx.xxx.xxx:80  &lt;VirtualHost xxx.xxx.xxx.xxx:80&gt;     ServerName mydomain.com     ServerAlias www.mydomain.com     DocumentRoot /var/www/html/w3prod     ServerAdmin admin@localhost     UseCanonicalName Off     CustomLog /var/log/httpd/w3prod.mydomain.com combined     ErrorLog /var/log/httpd/w3prod_error.mydomain.com &lt;/VirtualHost&gt; &lt;VirtualHost xxx.xxx.xxx.xxx:80&gt;     ServerName picfarm.mydomain.com     ServerAlias www.picfarm.mydomain.com     DocumentRoot /var/www/html/picfarm     ServerAdmin admin@localhost     UseCanonicalName Off     CustomLog /var/log/httpd/picfarm.mydomain.com combined     ErrorLog /var/log/httpd/picfarm_error.mydomain.com &lt;/VirtualHost&gt; &lt;VirtualHost xxx.xxx.xxx.xxx:80&gt;     ServerName test.mydomain.com     ServerAlias www.test.mydomain.com     DocumentRoot /var/www/html/engine-test     ServerAdmin admin@localhost     UseCanonicalName Off     CustomLog /var/log/httpd/test.mydomain.com combined     ErrorLog  /var/log/httpd/test_error.mydomain.com     ProxyRequests Off     ProxyPreserveHost On     &lt;Proxy *&gt;             Order deny,allow             Allow from all     &lt;/Proxy&gt;     ProxyPass /bosh http://xxx.xxx.xxx.xxx:7070/http-bind/     ProxyPassReverse /bosh http://xxx.xxx.xxx.xxx:7070/http-bind/     ProxyPass / http://xxx.xxx.xxx.xxx:8080/     ProxyPassReverse / http://xxx.xxx.xxx.xxx:8080/ &lt;/VirtualHost&gt;   Any help would be appreciated. Thanks! Can I purge configuration files after I've removed the package? I was doing a package removal with apt-get remove but then realized I should have done a --purge along with it to remove the configuration files.  Can I remove the packages configuration files easily or do I need to reinstall the package and then remove with a --purge? I designed a poster in CorelDraw X5 for printing purposes. I was told by the Printshop guy to use colors only in CMYK. For the most part I did, I don't know why I missed it but I used one color in RGB. I liked this color so much that I've used it at many places. So, current situation is that some colors are in RGB and some are in CMYK. So, I want to convert all RGB to CMYK and thought the problem would be solved. But now I'm actually facing a lot of trouble. The colors are not at all same. I hate the colors that it is showing me.  This is the color I used in RGB:    When I changed the "Model" to CMYK, the color it shows is really different. As you can see in the picture below, it's too dull:    The RGB values of both colors are not the same. What can I do to get the same color in CMYK? I did a little bit of reading here and there. They say, that you can't get same. In that case, what is the closest color that I can get? Is there any hint of of the first Wizarding War being an international event? Is there any hint that the MoM or anywhere else got support in combating voldemort the first time around? Or is everything completely UK-centric?  I can't remember anyone in the second war being specifically sent from europe to help, even though we see international wizards in book 4. But I don't think all the events of the first war are covered in the books.  So are other bodies like the MoM involved in the first war, or was it isolated in the UK? I've only been able to resolve this far  $$ d \mid n \Rightarrow \exists l \in \mathbb{Z}\; \textrm{such that} \; n=dl \Rightarrow x^{q^n} - x = x^{q^{dl}} - x.$$  I can't move forward. How much sleep do adults actually need? The common consensus is that most adults should get 8 hours of sleep a night.  However, sleep needs are highly variable, with some people needing more to function properly, and some gaining little benefit past just a few hours. I'm trying to learn more about the statistics here.  I'd imagine sleep needs would fit a normal distribution, with a median of around 8 hours and a standard deviation of around an hour. The  would then put 68% of adults in the 7-9 hour range, 95% in the 6-10 hour range, and 99.7% in the 5-11 hour range, but that's just a guess.  Has this distribution been studied, and where? Which prepositions are followed by accusative pronouns instead of reflexive pronouns? I have read answers to questions like  but I couldn't find a general rule for using "you" or "yourself", "him" or "himself" that could explain things I see in some examples.  For example, I think that one normally say (according to examples I see in ):   You bring something with you. You have something in you. You have something on you. You pressed her to you.   But on the other hand one would say:   You draw attention to yourself. He killed himself. You can try it out for yourself.   As a general rule, it seems that the reflexive pronoun is used when the object is the same as the subject of the verb. But for prepositional phrases, it seems more complicated. Do some prepositions (like "with", "in", "on") always come with the accusative form of the pronoun, and some other (like "for") don't? What about "to", that seems to be followed by both in different circumstances? I just installed Dufour on my Windows 7 Lenovo ThinkCentre desktop. When I open 2.0.1 I get this error window:    And when I try to add the 'Add Delimited Text Layer' plugin I get this message:    When I click 'OK' the program closes.   Any help is greatly appreciated - thanks. Turning off auto-maximizing of windows in 14.04 I know this has been asked for other Ubuntu releases, but the solutions posted are not working for me in 14.04. I've installed CCSM and turned off the grid option, but the windows still maximize when dragging to the top of the screen. I've dealt with it for a while but it's getting rather obnoxious. Anyone else had this problem and come across a solution?  EDIT:  This is happening in Gnome Classic, but not Gnome 3