Why i'm getting exception IOExceptiob: The process cannot access the file....because it is being used by another process ?

public list<string> lockedthreads(string filename)          {              string fname = "http://rotter.net/cgi-bin/forum/dcboard.cgi?az=list&forum=scoops1&mm=3&archive=";              uri uri = new uri(fname);              string str = "";              using (webclient client = new webclient())              {                  client.headers.add(httprequestheader.contenttype, "charset=windows-1255");                  str = client.downloadstring(fname);                  client.downloadfileasync(uri, @"c:\temp\scoopstest\scooptest.html");              }              filename = @"c:\temp\scoopstest\scooptest.html";                string t1 = "";              list<int> numberoflines = new list<int>();              list<string> lockedthreads = new list<string>();              list<string> lockedlinks = new list<string>();              string[] lines = file.readalllines(filename);

i'm using webclient download html file assign html content string , save hard disk.

then assign file name string called filename.

the exception on line:

string[] lines = file.readalllines(filename);

system.io.ioexception unhandled    hresult=-2147024864    message=the process cannot access file 'c:\temp\scoopstest\scooptest.html' because being used process.    source=mscorlib    stacktrace:         @ system.io.__error.winioerror(int32 errorcode, string maybefullpath)         @ system.io.filestream.init(string path, filemode mode, fileaccess access, int32 rights, boolean userights, fileshare share, int32 buffersize, fileoptions options, security_attributes secattrs, string msgpath, boolean bfromproxy, boolean uselongpath, boolean checkhost)         @ system.io.filestream..ctor(string path, filemode mode, fileaccess access, fileshare share, int32 buffersize, fileoptions options, string msgpath, boolean bfromproxy, boolean uselongpath, boolean checkhost)         @ system.io.streamreader..ctor(string path, encoding encoding, boolean detectencodingfrombyteordermarks, int32 buffersize, boolean checkhost)         @ system.io.streamreader..ctor(string path, encoding encoding)         @ system.io.file.internalreadalllines(string path, encoding encoding)         @ system.io.file.readalllines(string path)         @ scrolllabeltest.listsextractions.lockedthreads(string filename) in e:\scrolllabel\scrolllabel\scrolllabel\listsextractions.cs:line 197         @ scrolllabeltest.listsextractions.filterlockednews(list`1 filtered_lnl, string filename) in e:\scrolllabel\scrolllabel\scrolllabel\listsextractions.cs:line 475         @ scrolllabeltest.listsextractions.ext(string filename) in e:\scrolllabel\scrolllabel\scrolllabel\listsextractions.cs:line 362         @ scrolllabeltest.form1.scrollnews() in e:\scrolllabel\scrolllabel\scrolllabel\form1.cs:line 324         @ scrolllabeltest.form1..ctor() in e:\scrolllabel\scrolllabel\scrolllabel\form1.cs:line 109         @ scrolllabeltest.program.main() in e:\scrolllabel\scrolllabel\scrolllabel\program.cs:line 18         @ system.appdomain._nexecuteassembly(runtimeassembly assembly, string[] args)         @ system.appdomain.executeassembly(string assemblyfile, evidence assemblysecurity, string[] args)         @ microsoft.visualstudio.hostingprocess.hostproc.runusersassembly()         @ system.threading.threadhelper.threadstart_context(object state)         @ system.threading.executioncontext.runinternal(executioncontext executioncontext, contextcallback callback, object state, boolean preservesyncctx)         @ system.threading.executioncontext.run(executioncontext executioncontext, contextcallback callback, object state, boolean preservesyncctx)         @ system.threading.executioncontext.run(executioncontext executioncontext, contextcallback callback, object state)         @ system.threading.threadhelper.threadstart()    innerexception:   

the downloadfileasync method not block calling thread file.readalllines method may executed before file has been downloaded.
if on .net 4.5 can await downloadfiletaskasync method download file asynchronously , wait execute remainder of method until file has been downloaded without blocking thread during meantime:

public async task<list<string>> lockedthreads(string filename)         {             string fname = "http://rotter.net/cgi-bin/forum/dcboard.cgi?az=list&forum=scoops1&mm=3&archive=";             uri uri = new uri(fname);             string str = "";             using (webclient client = new webclient())             {                 client.headers.add(httprequestheader.contenttype, "charset=windows-1255");                 str = client.downloadstring(fname);                 await client.downloadfiletaskasync(uri, @"c:\temp\scoopstest\scooptest.html");             }             filename = @"c:\temp\scoopstest\scooptest.html";              string t1 = "";             list<int> numberoflines = new list<int>();             list<string> lockedthreads = new list<string>();             list<string> lockedlinks = new list<string>();             string[] lines = file.readalllines(filename);              return ...;         } 

if not on .net 4.5, should execute remainder of method in event handler downloadfilecompleted of webclient:

string file;         public list<string> lockedthreads(string filename)         {             string fname = "http://rotter.net/cgi-bin/forum/dcboard.cgi?az=list&forum=scoops1&mm=3&archive=";             uri uri = new uri(fname);             string str = "";             using (webclient client = new webclient())             {                 client.headers.add(httprequestheader.contenttype, "charset=windows-1255");                 str = client.downloadstring(fname);                 client.downloadfileasync(uri, @"c:\temp\scoopstest\scooptest.html");                 client.downloadfilecompleted += client_downloadfilecompleted;             }             file = @"c:\temp\scoopstest\scooptest.html";               return ....;         }          void client_downloadfilecompleted(object sender, asynccompletedeventargs e)         {             string t1 = "";             list<int> numberoflines = new list<int>();             list<string> lockedthreads = new list<string>();             list<string> lockedlinks = new list<string>();             string[] lines = file.readalllines(filename);         } 

...or use synchronous version of downloadfile method:

public list<string> lockedthreads(string filename)         {             string fname = "http://rotter.net/cgi-bin/forum/dcboard.cgi?az=list&forum=scoops1&mm=3&archive=";             uri uri = new uri(fname);             string str = "";             using (webclient client = new webclient())             {                 client.headers.add(httprequestheader.contenttype, "charset=windows-1255");                 str = client.downloadstring(fname);                 client.downloadfile(uri, @"c:\temp\scoopstest\scooptest.html");             }             filename = @"c:\temp\scoopstest\scooptest.html";              string t1 = "";             list<int> numberoflines = new list<int>();             list<string> lockedthreads = new list<string>();             list<string> lockedlinks = new list<string>();             string[] lines = file.readalllines(filename);         }  

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