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  • Are there concurrency problems when using -performSelector:withObject:afterDelay: ?

    - by mystify
    For example, I often use this: [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:someDelay]; Now, lets say I call this 10 times to perform at the exact same delay, like: [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; [self performSelector:@selector(doSomethingAfterDelay:) withObject:someObject afterDelay:2.0]; - (void)doSomethingAfterDelay:(id)someObject { /* access an array, read stuff, write stuff, do different things that would suffer in multithreaded environments .... all operations are nonatomic! */ } I have observed pretty strange behavior when doing things like this. For my understanding, this method schedules a timer to fire on the current thread, so in this case the main thread. But since it doesn't create new threads, it actually should not be possible to run into concurrency problems, right?

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  • How to display HTML-like table data on iPhone?

    - by Jason
    I have a set of data in a matrix which I would like to display in my iPhone app with all of the rows and columns intact. Everything I can find on the web dealing with "tables iPhone" gives me information on UITableView, which only lets you show a list of items to the user - not an actual table in the HTML sense. What's the best way on the iPhone to display an actual table of data to the user, with column & row headings and table cells?

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  • Is MSDN referencing a system.thread, a worker thread, an io thread or all three?

    - by w0051977
    Please see the warning below taken from the StreamWriter class specification (http://msdn.microsoft.com/en-us/library/system.io.streamwriter.aspx): "Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe." I understand that a W3WC process contains two thread pools i.e. worker threads and I/O threads. A worker thread could contain many threads of its own (if the application creates its own System.Thread instances). Does the warning only relate to System.Threads or does it relate to worker threads and I/O threads as well I.e. as the instance variables of the streamwriter class are not thread safe then does this mean that there would be problems if multiple worker threads access it eg if two users on two different web clients attempt to write to the log file at the same time, then could one lock out the other?

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  • Python Class Variables Question

    - by zyq524
    I have some doubt about python's class variables. As my understanding, if I define a class variable, which is declared outside the init() function, this variable will create only once as a static variable in C++. This seems right for some python types, for instance, dict and list type, but for those base type, e.g. int,float, is not the same. For example: class A: dict1={} list1=list() int1=3 def add_stuff(self, k, v): self.dict1[k]=v self.list1.append(k) self.int1=k def print_stuff(self): print self.dict1,self.list1,self.int1 a1 = A() a1.add_stuff(1, 2) a1.print_stuff() a2=A() a2.print_stuff() The output is: {1: 2} [1] 1 {1: 2} [1] 3 I understand the results of dict1 and list1, but why does int1 behavior different?

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  • Lua : How to check if one of the values associated with the specified key of a table is nil, from ap

    - by felace
    In lua, it's legal to do this : table={} bar if(table[key]==nil) foo However, using C API, I couldn't find way to check if there's a nil value on the specified position. lua_getglobal(L,"table"); lua_gettable(L,key); If there's a nil value stored in table[key], lua_gettable would give me the "unprotected error in call to Lua API (attempt to index a nil value)" message. Is there any way to check if there's actually something associated with that key, before actually pushing the key to do so ?

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  • Update table instantly or “Bulk” Update in database later? And is it advisable?

    - by Mestika
    Hi, I have a question regarding a semi-constant update in a database. In short it is regarding a checkout function on a web page, which each time the checkout function is evoked it do five steps. I want to try to optimize this function and have my eye on a step where I update a table each time the checkout is performed. I take the information retrieved from the shopping cart and then update the table in question. I do have some indexes on the table, the gain from those are greater than leaving them so this is a cost I’m willing to take. Now, my question is. Could it in some way regarding to performance be better to not update the table instantly but collect every checkout items and save them in some way (maybe in a file) and then at a specific time (or several times) at day take this file and then update the table with the new information. Then I started thinking about if there was a possibility to use some sort of Bulk Update to take a file, hashmap, array (or?) and then update it. And I’m using IBM DB2 version 9.7 Mestika

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  • I can get access to object's properties if method is called from anonymous function, but I can't do

    - by Kirzilla
    Hello, $.Comment = function() { this.alertme = "Alert!"; } $.Comment.prototype.send = function() { var self = this; $.post( self.url, { 'somedata' : self.somedata }, function(data) { //using anonymous function to call object's method self.callback(data); } ); } $.Comment.prototype.callback = function(data) { alert(this.alertme); } This code works great when I'm calling $.Comment.send(), but this code won't work... $.Comment.prototype.send = function() { var self = this; $.post( self.url, { 'somedata' : self.somedata }, self.callback //using direct access to method ); } Please, could you explain me why? Thank you

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  • How to retain a row which is foreign key in another table and remove other duplicate rows?

    - by Mithril
    I have two table: A: id code 1 A1 2 A1 3 B1 4 B1 5 C1 6 C1 ===================== B: id Aid 1 1 2 4 (B doesn't contain the Aid which link to code C1) Let me explain the overall flow: I want to make each row in table A have different code(by delete duplicate),and I want to retain the Aid which I can find in table B.If Aid which not be saved in table B,I retain the id bigger one. so I can not just do something as below: DELETE FROM A WHERE id NOT IN (SELECT MAX(id) FROM A GROUP BY code, ) I can get each duplicate_code_groups by below sql statement: SELECT code FROM A GROUP BY code HAVING COUNT(*) > 1 Is there some code in sql like for (var ids in duplicate_code_groups){ for (var id in ids) { if (id in B){ return id } } return max(ids) } and put the return id into a idtable?? I just don't know how to write such code in sql. then I can do DELETE FROM A WHERE id NOT IN idtable

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  • How can I get the contents of my table with dynamic row adding?

    - by user359706
    how to retrieve from the server-side contained a table html constructed this way: <table id="myTable"> <tr> <th> <input type="text"> name </th> <th> <input type="text"> quantity </th> </tr> <tr> <th> <input id="name_1"> phone </th> <th> <input id="quantity_1"> 15 </th> </tr> <tr> <th> <input ="name_2"> id mp3 </th> <th> <input id="quantity_2"> 26 <</th> </tr> ... I can not make use of <asp:Table> ... because for technical reasons I did not find a solution following this post: http://stackoverflow.com/questions/3003912/how-to-dynamic-adding-rows-into-asp-net-table How can retrieve the contents values of my table (dynamic) for each row. Rows will be added in client-side js Thank you.

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  • In SQL Server 2000, how to delete the specified rows in a table that does not have a primary key?

    - by Yousui
    Hi, Let's say we have a table with some data in it. IF OBJECT_ID('dbo.table1') IS NOT NULL BEGIN DROP TABLE dbo.table1; END CREATE TABLE table1 ( DATA INT ); --------------------------------------------------------------------- -- Generating testing data --------------------------------------------------------------------- INSERT INTO dbo.table1(data) SELECT 100 UNION ALL SELECT 200 UNION ALL SELECT NULL UNION ALL SELECT 400 UNION ALL SELECT 400 UNION ALL SELECT 500 UNION ALL SELECT NULL; How to delete the 2nd, 5th, 6th records in the table? The order id defined by the following query. SELECT data FROM dbo.table1 ORDER BY data DESC; Note, this is in SQL Server 2000 environment. Thanks.

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  • In Android, does _id have to be present in any table created?

    - by Andy
    I am trying to create a table to only has a foreign key, not a primary key. I am getting this error: java.lang.IllegalArgumentException: column '_id' does not exist I read a tutorial that the primary key must be _id, with no explanation. And that is fine. But what if I do not want a primary key! What if I only want a foreign key. I am assuming this is where my problem lies. The schemas below are what I have. But the third one is where I assume this is coming from. database.execSQL("CREATE TABLE events (" + "_id INTEGER PRIMARY KEY, event_name TEXT" + ")"); database.execSQL("CREATE TABLE reminders(_id INTEGER PRIMARY KEY, event_name TEXT" + ")"); database.execSQL("CREATE TABLE events_info (_id INTEGER, event_name TEXT, all_day INTEGER, " + "start_date INTEGER, start_time INTEGER, end_date INTEGER, end_time INTEGER," + " location TEXT, reminder_id INTEGER, notes TEXT, repeat TEXT," + "FOREIGN KEY(_id) REFERENCES events(_id), FOREIGN KEY(reminder_id) REFERENCES reminders(_id))" );

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  • How do I overflow text to the left in a table?

    - by remack
    I have a table with fixed layout. On overflow, the contents of cells should clip from the left instead of the right. That is, if the width of the TD is less than the width of the text, the cell below should display "67890" instead of "12345". This needs to work in IE7+ at minimum. Is there a way to do this in css without any JavaScript? <table style="table-layout:fixed"> <tr> <TD> 12334567890 </TD> </tr> </table>

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  • How to make a staging table in ms sql 2005?

    - by chobo2
    Hi I heard about doing staging tables and I am wondering how you actually do it. I want to do a sqlbulk copy into a staging table. Then then update the real table. I heard in mssql 2008 that you can use something called merge but I am using ms sql 2005 so I heard I have to use a update inner join? I am not sure how that would look like(I am guessing best way would be to write it in SP). Also the staging table needs to be able to handle concurrent updates. I was thinking of putting another column in the staged as GUID so that way I know which records belong to which group and when it is time to delete the records from the staged table I can just use that. So can anyone show me any examples or tutorials on how to do it? Also how fast is this way? Say if your updating 50,000 records how long would that take(a guesstimate is fine)

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  • Please explain this delete top 100 SQL syntax

    - by Patrick
    Basically I want to do this: delete top( 100 ) from table order by id asc but MS SQL doesn't allow order in this position The common solution seems to be this: DELETE table WHERE id IN(SELECT TOP (100) id FROM table ORDER BY id asc) But I also found this method here: delete table from (select top (100) * from table order by id asc) table which has a much better estimated execution plan (74:26). Unfortunately I don't really understand the syntax, please can some one explain it to me? Always interested in any other methods to achieve the same result as well. EDIT: I'm still not getting it I'm afraid, I want to be able to read the query as I read the first two which are practically English. The above queries to me are: delete the top 100 records from table, with the records ordered by id ascending delete the top 100 records from table where id is anyone of (this lot of ids) delete table from (this lot of records) table I can't change the third one into a logical English sentence... I guess what I'm trying to get at is how does this turn into "delete from table (this lot of records)". The 'from' seems to be in an illogical position and the second mention of 'table' is logically superfluous (to me).

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  • method works fine, until it is called in a function, then UnboundLocalError

    - by user1776100
    I define a method called dist, to calculate the distance between two points which I does it correctly when directly using the method. However, when I get a function to call it to calculate the distance between two points, I get UnboundLocalError: local variable 'minkowski_distance' referenced before assignment edit sorry, I just realised, this function does work. However I have another method calling it that doesn't. I put the last method at the bottom This is the method: class MinkowskiDistance(Distance): def __init__(self, dist_funct_name_str = 'Minkowski distance', p=2): self.p = p def dist(self, obj_a, obj_b): distance_to_power_p=0 p=self.p for i in range(len(obj_a)): distance_to_power_p += abs((obj_a[i]-obj_b[i]))**(p) minkowski_distance = (distance_to_power_p)**(1/p) return minkowski_distance and this is the function: (it basically splits the tuples x and y into their number and string components and calculates the distance between the numeric part of x and y and then the distance between the string parts, then adds them. def total_dist(x, y, p=2, q=2): jacard = QGramDistance(q=q) minkowski = MinkowskiDistance(p=p) x_num = [] x_str = [] y_num = [] y_str = [] #I am spliting each vector into its numerical parts and its string parts so that the distances #of each part can be found, then summed together. for i in range(len(x)): if type(x[i]) == float or type(x[i]) == int: x_num.append(x[i]) y_num.append(y[i]) else: x_str.append(x[i]) y_str.append(y[i]) num_dist = minkowski.dist(x_num,y_num) str_dist = I find using some more steps #I am simply adding the two types of distance to get the total distance: return num_dist + str_dist class NearestNeighbourClustering(Clustering): def __init__(self, data_file, clust_algo_name_str='', strip_header = "no", remove = -1): self.data_file= data_file self.header_strip = strip_header self.remove_column = remove def run_clustering(self, max_dist, p=2, q=2): K = {} #dictionary of clusters data_points = self.read_data_file() K[0]=[data_points[0]] k=0 #I added the first point in the data to the 0th cluster #k = number of clusters minus 1 n = len(data_points) for i in range(1,n): data_point_in_a_cluster = "no" for c in range(k+1): distances_from_i = [total_dist(data_points[i],K[c][j], p=p, q=q) for j in range(len(K[c]))] d = min(distances_from_i) if d <= max_dist: K[c].append(data_points[i]) data_point_in_a_cluster = "yes" if data_point_in_a_cluster == "no": k += 1 K[k]=[data_points[i]] return K

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  • referencing struct fields in c with square brackets and an index instead of . and ->?

    - by lsiebert
    Assuming I have a structure such as: typedef struct { char * string1; char * string2; } TWO_WORDS; such that all the fields are of the same type, and my main has TWO_WORDS tw; can I reference string1 with tw[0] and string2 with two[1]? If so: is this part of the c standard? do i have to cast the struct to an array first? what about fields which are different sizes in memory what about fields which are different types but the same size? can you do pointer arithmetic within a structure? -

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