Search Results

Search found 4621 results on 185 pages for 'scott lock'.

Page 4/185 | < Previous Page | 1 2 3 4 5 6 7 8 9 10 11 12  | Next Page >

• Lock Windows keyboard and mouse but still display screen normally

  - by Stephen Lacy

  I'm using windows 7, I have a dual monitor display. It displays important information related to the business, I'd rather that random users that walk in can't just walk over to it and start using the computer with the same access rights as the user the monitoring software is running as. What I would like is if any time someone presses a button on the keyboard including alt-ctrl-delete all that would appear is a dialog asking for a password. Then I can click cancel and it will return to showing the data I want displayed. ClearLock doesn't work I tried it btw

  Read the article

• Difference Between Monitor & Lock?

  - by Goober

  What's the difference between a monitor and a lock? If a lock is simply an implementation of mutual exclusion, then is a monitor simply a way of making use of the waiting time inbetween method executions? A good explanation would be really helpful thanks.... regards

  Read the article

• [PHP] Read and write to a file while keeping lock

  - by Znarkus

  Hi! I am making a simple page load counter by storing the current count in a file. This is how I want to do this: Lock the file Read the current count Increment it Write new count Unlock file/close it Can this be done? As I understand it, the file can't be written to without losing the lock. The only way I have come up with to tackle this, is to write a character using "r+" mode, and then counting characters.

  Read the article

• C# Locking an object that is reassigned in lock block

  - by Theo Zographos

  Hello, I have this code in a class: private static MyObject _locker = new MyObject(); ... lock (_locker) { ... _locker = new MyObject(); ... } Will it keep the lock on _locker ?

  Read the article

• Why was Mr. Scott Scottish?

  - by iamjames

  It's a good question:  of all the engineers in the world, why choose a Scottish engineer?  The Gene Roddenberry probably chose a Scottish engineer because of this guy: That's James Watt, the same guy the unit of energy watt is named after.  He was a Scottish inventor and mechancial engineer who built the first made significant improvements to the steam engine.  Made sense in the 60's, however given the past hundred years if they were to make a new Star Trek they might have started with a German engineer (or maybe Japanese), but since World War II had ended barely 20 years earlier the 20-somethings that had survived the war were now 40-somethings and seeing a German engineer probably wouldn't have gone over too well.

  Read the article

• Ubuntu 13.10 japanese keyboard layout intercepts Caps Lock

  - by Envek

  I've installed Ubuntu 13.10 (clean install on new machine), there are lot of changes for configuring keyboard layouts and I've tried to configure it as I've used earlier: Englis (US), Russian and Japanese (Anthy) with switching between them with Caps Lock key. (See screenshot) Caps Lock switching works fine between Russian and English and vice-versa, but with Japanese I can switch only TO Japanese (not FROM), in Japanese layout Caps Lock starting to work as usual Caps Lock (as a switch between small and BIG letters), so I need to use mouse to switch back to Ru or En layout. This happens ONLY with Japanese layouts (I've tried also simply "Japanese" and "Japanese (Kana)"), not with Chinese, Korean or anything else. I'm not sure who is blame for that, is it ibus-anthy or anything. Please help, I want to use Caps Lock to switch between all layouts. Also, I've created a bug in the LaunchPad: https://bugs.launchpad.net/ubuntu/+source/gnome-control-center/+bug/1247363

  Read the article

• Looking for a lock-free RT-safe single-reader single-writer structure

  - by moala

  Hi, I'm looking for a lock-free design conforming to these requisites: a single writer writes into a structure and a single reader reads from this structure (this structure exists already and is safe for simultaneous read/write) but at some time, the structure needs to be changed by the writer, which then initialises, switches and writes into a new structure (of the same type but with new content) and at the next time the reader reads, it switches to this new structure (if the writer multiply switches to a new lock-free structure, the reader discards these structures, ignoring their data). The structures must be reused, i.e. no heap memory allocation/free is allowed during write/read/switch operation, for RT purposes. I have currently implemented a ringbuffer containing multiple instances of these structures; but this implementation suffers from the fact that when the writer has used all the structures present in the ringbuffer, there is no more place to change from structure... But the rest of the ringbuffer contains some data which don't have to be read by the reader but can't be re-used by the writer. As a consequence, the ringbuffer does not fit this purpose. Any idea (name or pseudo-implementation) of a lock-free design? Thanks for having considered this problem.

  Read the article

• Rails running multiple delayed_job - lock tables

  - by pepernik

  Hey. I use delayed_job for background processing. I have 8 CPU server, MySQL and I start 7 delayed_job processes RAILS_ENV=production script/delayed_job -n 7 start Q1: I'm wondering is it possible that 2 or more delayed_job processes start processing the same process (the same record-row in the database delayed_jobs). I checked the code of the delayed_job plugin but can not find the lock directive in a way it should be. I think each process should lock the database table before executing an UPDATE on lock_by column. They lock the record simply by updating the locked_by field (UPDATE delayed_jobs SET locked_by...). Is that really enough? No locking needed? Why? I know that UPDATE has higher priority than SELECT but I think this does not have the effect in this case. My understanding of the multy-threaded situation is: Process1: Get waiting job X. [OK] Process2: Get waiting jobs X. [OK] Process1: Update locked_by field. [OK] Process2: Update locked_by field. [OK] Process1: Get waiting job X. [Already processed] Process2: Get waiting jobs X. [Already processed] I think in some cases more jobs can get the same information and can start processing the same process. Q2: Is 7 delayed_jobs a good number for 8CPU server? Why yes/not. Thx 10x!

  Read the article

• lock shared data using c#

  - by menacheb

  Hi, I have a program (C#) with a list of tests to do. Also, I have two thread. one to add task into the list, and one to read and remove from it the performed tasks. I'm using the 'lock' function each time one of the threads want to access to the list. Another thing I want to do is, if the list is empty, the thread who need to read from the list will sleep. and wake up when the first thread add a task to the list. Here is the code I wrote: ... List<String> myList = new List(); Thread writeThread, readThread; writeThread = new Thread(write); writeThread.Start(); readThraed = new Thread(read); readThread.Start(); ... private void write() { while(...) { ... lock(myList) { myList.Add(...); } ... if (!readThread.IsAlive) { readThraed = new Thread(read); readThread.Start(); } ... } ... } private void read() { bool noMoreTasks = false; while (!noMoreTasks) { lock (MyList)//syncronize with the ADD func. { if (dataFromClientList.Count > 0) { String task = myList.First(); myList.Remove(task); } else { noMoreTasks = true; } } ... } readThread.Abort(); } Apparently I did it wrong, and it's not performed as expected (The readTread does't read from the list). Does anyone know what is my problem, and how to make it right? Many thanks,

  Read the article

• Lock Free Queue -- Single Producer, Multiple Consumers

  - by Shirish

  Hello, I am looking for a method to implement lock-free queue data structure that supports single producer, and multiple consumers. I have looked at the classic method by Maged Michael and Michael Scott (1996) but their version uses linked lists. I would like an implementation that makes use of bounded circular buffer. Something that uses atomic variables? On a side note, I am not sure why these classic methods are designed for linked lists that require a lot of dynamic memory management. In a multi-threaded program, all memory management routines are serialized. Aren't we defeating the benefits of lock-free methods by using them in conjunction with dynamic data structures? I am trying to code this in C/C++ using pthread library on a Intel 64-bit architecture. Thank you, Shirish

  Read the article

• optimistic lock-free FIFO queues impl?

  - by uray

  is there any C++ implementation (source codes) of "optmistic approach to lock-free FIFO queues" algorithm?

  Read the article

• Persistent SQL Table lock from C#

  - by Chris

  I'm trying to create a persistent SQL (SQL Server 2005) lock on a table level. I'm not updating/querying the specified table, but I need to prevent a third party application from updating the locked table as a means to prevent transactions from being posted (the table I wish to lock is the key on their transaction that interferes with my processing). From my experience the table is only locked for the time a specific transaction is taking place. Any ideas? The 3rd party developer has logged this feature as an enhancement, but since they are in the middle of rolling out a major release I can expect to wait at least 6 months for this. I know that this isn't a great solution, since their software will fall over but it is of a critical enough nature that we're willing to live with the consequences.

  Read the article

• ASP.NET lock thread method

  - by Peter

  Hello, I'm developing an ASP.NET forms webapplication using C#. I have a method which creates a new Order for a customer. It looks similar to this; private string CreateOrder(string userName) { // Fetch current order Order order = FetchOrder(userName); if (order.OrderId == 0) { // Has no order yet, create a new one order.OrderNumber = Utility.GenerateOrderNumber(); order.Save(); } return order; } The problem here is, it is possible that 1 customer in two requests (threads) could cause this method to be called twice while another thread is also inside this method. This can cause two orders to be created. How can I properly lock this method, so it can only be executed by one thread at a time per customer? I tried; Mutex mutex = null; private string CreateOrder(string userName) { if (mutex == null) { mutex = new Mutex(true, userName); } mutex.WaitOne(); // Code from above mutex.ReleaseMutex(); mutex = null; return order; } This works, but on some occasions it hangs on WaitOne and I don't know why. Is there an error, or should I use another method to lock? Thanks

  Read the article

• ??ORACLE(?):PMON Release Lock

  - by Liu Maclean(???)

  ?????Oracle????????????PMON???????,??????ORACLE PROCESS,??cleanup dead process????release enqueue lock ,???cleanup latch? ????????????????, ????????????Pmon cleanup dead process?release lock??????????? ??Oracle=> MicroOracle, Maclean???????????Oracle behavior: SQL> select * from v$version; BANNER -------------------------------------------------------------------------------- Oracle Database 11g Enterprise Edition Release 11.2.0.3.0 - 64bit Production PL/SQL Release 11.2.0.3.0 - Production CORE    11.2.0.3.0      Production TNS for Linux: Version 11.2.0.3.0 - Production NLSRTL Version 11.2.0.3.0 - Production SQL> select * from global_name; GLOBAL_NAME -------------------------------------------------------------------------------- www.oracledatabase12g.com SQL> select pid,program  from v$process;        PID PROGRAM ---------- ------------------------------------------------          1 PSEUDO          2 [email protected] (PMON)          3 [email protected] (PSP0)          4 [email protected] (VKTM)          5 [email protected] (GEN0)          6 [email protected] (DIAG)          7 [email protected] (DBRM)          8 [email protected] (PING)          9 [email protected] (ACMS)         10 [email protected] (DIA0)         11 [email protected] (LMON)         12 [email protected] (LMD0)         13 [email protected] (LMS0)         14 [email protected] (RMS0)         15 [email protected] (LMHB)         16 [email protected] (MMAN)         17 [email protected] (DBW0)         18 [email protected] (LGWR)         19 [email protected] (CKPT)         20 [email protected] (SMON)         21 [email protected] (RECO)         22 [email protected] (RBAL)         23 [email protected] (ASMB)         24 [email protected] (MMON)         25 [email protected] (MMNL)         26 [email protected] (MARK)         27 [email protected] (D000)         28 [email protected] (SMCO)         29 [email protected] (S000)         30 [email protected] (LCK0)         31 [email protected] (RSMN)         32 [email protected] (TNS V1-V3)         33 [email protected] (W000)         34 [email protected] (TNS V1-V3)         35 [email protected] (TNS V1-V3)         37 [email protected] (ARC0)         38 [email protected] (ARC1)         40 [email protected] (ARC2)         41 [email protected] (ARC3)         43 [email protected] (GTX0)         44 [email protected] (RCBG)         46 [email protected] (QMNC)         47 [email protected] (TNS V1-V3)         48 [email protected] (TNS V1-V3)         49 [email protected] (Q000)         50 [email protected] (Q001)         51 [email protected] (GCR0) SQL> drop table maclean; Table dropped. SQL> create table maclean(t1 int); Table created. SQL> insert into maclean values(1); 1 row created. SQL> commit; Commit complete. ?????????, ?????????:PID=2  PMONPID=11 LMONPID=18 LGWRPID=20 SMONPID=12 LMD ??????2???”enq: TX – row lock contention”?????,???KILL??????,??????PMON?recover dead process?release TX lock: PROCESS A: QL> select addr,spid,pid from v$process where addr = ( select paddr from v$session where sid=(select distinct sid from v$mystat)); ADDR             SPID                            PID ---------------- ------------------------ ---------- 00000000BD516B80 17880                            46 SQL> select distinct sid from v$mystat;        SID ----------         22 SQL> update maclean set t1=t1+1; 1 row updated. PROCESS B SQL> select addr,spid,pid from v$process where addr = ( select paddr from v$session where sid=(select distinct sid from v$mystat)); ADDR             SPID                            PID ---------------- ------------------------ ---------- 00000000BD515AD0 17908                            45 SQL> update maclean set t1=t1+1; HANG.............. PROCESS B ??"enq: TX – row lock contention"?HANG? ????PROCESS C?? ?SMON?10500 event trace ??PMON?KST TRACE: SQL> set linesize 200 pagesize 1400 SQL> select * from v$lock where sid=22; ADDR             KADDR                   SID TY        ID1        ID2      LMODE    REQUEST      CTIME      BLOCK ---------------- ---------------- ---------- -- ---------- ---------- ---------- ---------- ---------- ---------- 00000000BDCD7618 00000000BDCD7670         22 AE        100          0          4          0         48          2 00007F63268A9E28 00007F63268A9E88         22 TM      77902          0          3          0         32          2 00000000B9BB4950 00000000B9BB49C8         22 TX     458765        892          6          0         32          1 PROCESS A holde?ENQUEUE LOCK??? AE?TM?TX SQL> alter system switch logfile; System altered. SQL> alter system checkpoint; System altered. SQL> alter system flush buffer_cache; System altered. SQL> alter system set "_trace_events"='10000-10999:255:2,20,33'; System altered. SQL> ! kill -9 17880 KILL PROCESS A ???PROCESS B??update ?PMON ? PROCESS B ?errorstack ?KST TRACE????? SQL> oradebug setorapid 2; Oracle pid: 2, Unix process pid: 17533, image: [email protected] (PMON) SQL> oradebug dump errorstack 4; Statement processed. SQL> oradebug tracefile_name /s01/orabase/diag/rdbms/vprod/VPROD1/trace/VPROD1_pmon_17533.trc SQL> oradebug setorapid 45; Oracle pid: 45, Unix process pid: 17908, image: [email protected] (TNS V1-V3) SQL> oradebug dump errorstack 4; Statement processed. SQL>oradebug tracefile_name /s01/orabase/diag/rdbms/vprod/VPROD1/trace/VPROD1_ora_17908.trc ??PMON? KST TRACE: 2012-05-18 10:37:34.557225 :8001ECE8:db_trace:ktur.c@5692:ktugru(): [10444:2:1] next rollback uba: 0x00000000.0000.00 2012-05-18 10:37:34.557382 :8001ECE9:db_trace:ksl2.c@16009:ksl_update_post_stats(): [10005:2:1] KSL POST SENT postee=18 num=4 loc='ksa2.h LINE:285 ID:ksasnd' id1=0 id2=0 name=   type=0 2012-05-18 10:37:34.557514 :8001ECEA:db_trace:ksq.c@8540:ksqrcli(): [10704:2:1] ksqrcl: release TX-0007000d-0000037c mode=X 2012-05-18 10:37:34.558819 :8001ECF0:db_trace:ksl2.c@16009:ksl_update_post_stats(): [10005:2:1] KSL POST SENT postee=45 num=5 loc='kji.h LINE:3418 ID:kjata: wake up enqueue owner' id1=0 id2=0 name=   type=0 2012-05-18 10:37:34.559047 :8001ECF8:db_trace:ksl2.c@16009:ksl_update_post_stats(): [10005:2:1] KSL POST SENT postee=12 num=6 loc='kjm.h LINE:1224 ID:kjmpost: post lmd' id1=0 id2=0 name=   type=0 2012-05-18 10:37:34.559271 :8001ECFC:db_trace:ksq.c@8826:ksqrcli(): [10704:2:1] ksqrcl: SUCCESS 2012-05-18 10:37:34.559291 :8001ECFD:db_trace:ktu.c@8652:ktudnx(): [10813:2:1] ktudnx: dec cnt xid:7.13.892 nax:0 nbx:0 2012-05-18 10:37:34.559301 :8001ECFE:db_trace:ktur.c@3198:ktuabt(): [10444:2:1] ABORT TRANSACTION - xid: 0x0007.00d.0000037c 2012-05-18 10:37:34.559327 :8001ECFF:db_trace:ksq.c@8540:ksqrcli(): [10704:2:1] ksqrcl: release TM-0001304e-00000000 mode=SX 2012-05-18 10:37:34.559365 :8001ED00:db_trace:ksq.c@8826:ksqrcli(): [10704:2:1] ksqrcl: SUCCESS 2012-05-18 10:37:34.559908 :8001ED01:db_trace:ksq.c@8540:ksqrcli(): [10704:2:1] ksqrcl: release AE-00000064-00000000 mode=S 2012-05-18 10:37:34.559982 :8001ED02:db_trace:ksq.c@8826:ksqrcli(): [10704:2:1] ksqrcl: SUCCESS 2012-05-18 10:37:34.560217 :8001ED03:db_trace:ksfd.c@15379:ksfdfods(): [10298:2:1] ksfdfods:fob=0xbab87b48 aiopend=0 2012-05-18 10:37:34.560336 :GSIPC:kjcs.c@4876:kjcsombdi(): GSIPC:SOD: 0xbc79e0c8 action 3 state 0 chunk (nil) regq 0xbc79e108 batq 0xbc79e118 2012-05-18 10:37:34.560357 :GSIPC:kjcs.c@5293:kjcsombdi(): GSIPC:SOD: exit cleanup for 0xbc79e0c8 rc: 1, loc: 0x303 2012-05-18 10:37:34.560375 :8001ED04:db_trace:kss.c@1414:kssdch(): [10809:2:1] kssdch(0xbd516b80 = process, 3) 1 0 exit 2012-05-18 10:37:34.560939 :8001ED06:db_trace:kmm.c@10578:kmmlrl(): [10257:2:1] KMMLRL: Entering: flg(0x0) rflg(0x4) 2012-05-18 10:37:34.561091 :8001ED07:db_trace:kmm.c@10472:kmmlrl_process_events(): [10257:2:1] KMMLRL: Events: succ(3) wait(0) fail(0) 2012-05-18 10:37:34.561100 :8001ED08:db_trace:kmm.c@11279:kmmlrl(): [10257:2:1] KMMLRL: Reg/update: flg(0x0) rflg(0x4) 2012-05-18 10:37:34.563325 :8001ED0B:db_trace:kmm.c@12511:kmmlrl(): [10257:2:1] KMMLRL: Update: ret(0) 2012-05-18 10:37:34.563335 :8001ED0C:db_trace:kmm.c@12768:kmmlrl(): [10257:2:1] KMMLRL: Exiting: flg(0x0) rflg(0x4) 2012-05-18 10:37:34.563354 :8001ED0D:db_trace:ksl2.c@2598:kslwtbctx(): [10005:2:1] KSL WAIT BEG [pmon timer] 300/0x12c 0/0x0 0/0x0 wait_id=78 seq_num=79 snap_id=1 PMON??dead process A??????????TX Lock:ksqrcl: release TX-0007000d-0000037c mode=X ?????Post Process B,??Process B ?acquire?TX lock???????:KSL POST SENT postee=45 num=5 loc=’kji.h LINE:3418 ID:kjata: wake up enqueue owner’ id1=0 id2=0 name=   type=0 Process B???PMON??????????ksl2.c@14563:ksliwat(): [10005:45:151] KSL POST RCVD poster=2 num=5 loc=’kji.h LINE:3418 ID:kjata: wake up enqueue owner’ id1=0 id2=0 name=   type=0 fac#=3 posted=0×3 may_be_posted=1kslwtbctx(): [10005:45:151] KSL WAIT BEG [latch: ges resource hash list] 3162668560/0xbc827e10 91/0x5b 0/0×0 wait_id=14 seq_num=15 snap_id=1kslwtectx(): [10005:45:151] KSL WAIT END [latch: ges resource hash list] 3162668560/0xbc827e10 91/0x5b 0/0×0 wait_id=14 seq_num=15 snap_id=1 ?RAC????POST LMD(lock Manager)??,????????GES??:2012-05-18 10:37:34.559047 :8001ECF8:db_trace:ksl2.c@16009:ksl_update_post_stats(): [10005:2:1] KSL POST SENT postee=12 num=6 loc=’kjm.h LINE:1224 ID:kjmpost: post lmd’ id1=0 id2=0 name=   type=0 ??ksqrcl: release TX????????:ksq.c@8826:ksqrcli(): [10704:2:1] ksqrcl: SUCCESS ??PMON abort Process A???Transaction2012-05-18 10:37:34.559291 :8001ECFD:db_trace:ktu.c@8652:ktudnx(): [10813:2:1] ktudnx: dec cnt xid:7.13.892 nax:0 nbx:02012-05-18 10:37:34.559301 :8001ECFE:db_trace:ktur.c@3198:ktuabt(): [10444:2:1] ABORT TRANSACTION – xid: 0×0007.00d.0000037c ??Process A?????maclean??TM lock:ksq.c@8540:ksqrcli(): [10704:2:1] ksqrcl: release TM-0001304e-00000000 mode=SXksq.c@8826:ksqrcli(): [10704:2:1] ksqrcl: SUCCESS ??Process A?????AE ( Prevent Dropping an edition in use) lock:ksq.c@8540:ksqrcli(): [10704:2:1] ksqrcl: release AE-00000064-00000000 mode=Sksq.c@8826:ksqrcli(): [10704:2:1] ksqrcl: SUCCESS ??cleanup process Akjcs.c@4876:kjcsombdi(): GSIPC:SOD: 0xbc79e0c8 action 3 state 0 chunk (nil) regq 0xbc79e108 batq 0xbc79e118GSIPC:kjcs.c@5293:kjcsombdi(): GSIPC:SOD: exit cleanup for 0xbc79e0c8 rc: 1, loc: 0×303kss.c@1414:kssdch(): [10809:2:1] kssdch(0xbd516b80 = process, 3) 1 0 exit 0xbd516b80??PROCESS A ?paddr ???? kssdch???????? ??process???state object SO KSS: delete children of state obj. PMON ??kmmlrl()????instance goodness??update for session drop deltakmmlrl(): [10257:2:1] KMMLRL: Entering: flg(0×0) rflg(0×4)kmmlrl_process_events(): [10257:2:1] KMMLRL: Events: succ(3) wait(0) fail(0)kmmlrl(): [10257:2:1] KMMLRL: Reg/update: flg(0×0) rflg(0×4)kmmlrl(): [10257:2:1] KMMLRL: Update: ret(0)kmmlrl(): [10257:2:1] KMMLRL: Exiting: flg(0×0) rflg(0×4) ????????PMON???? 3s???”pmon timer”??kslwtbctx(): [10005:2:1] KSL WAIT BEG [pmon timer] 300/0x12c 0/0×0 0/0×0 wait_id=78 seq_num=79 snap_id=1

  Read the article

• detecting locked tables mysql (locked by LOCK TABLE)

  - by Marcin

  Hi guys, I would like to know whether is there an option to detect locked tables in mysql or no. I mean locked by LOCK TABLE table WRITE/READ command ? cheers, Marcin

  Read the article

• Is std::ifstream thread-safe & lock-free?

  - by Viet

  I intend to perform opening for reading a single file from many threads using std::ifstream. My concern is if std::ifstream is thread-safe & lock-free?

  Read the article

• Well tested C/C++ lock free queue?

  - by uj

  I am looking for a well-tested, publicly available C/C++ implementation of a lock free queue. I need at least multiple-producers/single-consumer functionality. Multiple-consumers is even better, if exists. I'm targetting VC's _Interlocked... intrinsics, though anything which is straight forward to port would be fine. Could anyone give any pointers?

  Read the article

• Lock free multiple readers single writer

  - by dummzeuch

  I have got an in memory data structure that is read by multiple threads and written by only one thread. Currently I am using a critical section to make this access threadsafe. Unfortunately this has the effect of blocking readers even though only another reader is accessing it. There are two options to remedy this: use TMultiReadExclusiveWriteSynchronizer do away with any blocking by using a lock free approach For 2. I have got the following so far (any code that doesn't matter has been left out): type TDataManager = class private FAccessCount: integer; FData: TDataClass; public procedure Read(out _Some: integer; out _Data: double); procedure Write(_Some: integer; _Data: double); end; procedure TDataManager.Read(out _Some: integer; out _Data: double); var Data: TDAtaClass; begin InterlockedIncrement(FAccessCount); try // make sure we get both values from the same TDataClass instance Data := FData; // read the actual data _Some := Data.Some; _Data := Data.Data; finally InterlockedDecrement(FAccessCount); end; end; procedure TDataManager.Write(_Some: integer; _Data: double); var NewData: TDataClass; OldData: TDataClass; ReaderCount: integer; begin NewData := TDataClass.Create(_Some, _Data); InterlockedIncrement(FAccessCount); OldData := TDataClass(InterlockedExchange(integer(FData), integer(NewData)); // now FData points to the new instance but there might still be // readers that got the old one before we exchanged it. ReaderCount := InterlockedDecrement(FAccessCount); if ReaderCount = 0 then // no active readers, so we can safely free the old instance FreeAndNil(OldData) else begin /// here is the problem end; end; Unfortunately there is the small problem of getting rid of the OldData instance after it has been replaced. If no other thread is currently within the Read method (ReaderCount=0), it can safely be disposed and that's it. But what can I do if that's not the case? I could just store it until the next call and dispose it there, but Windows scheduling could in theory let a reader thread sleep while it is within the Read method and still has got a reference to OldData. If you see any other problem with the above code, please tell me about it. This is to be run on computers with multiple cores and the above methods are to be called very frequently. In case this matters: I am using Delphi 2007 with the builtin memory manager. I am aware that the memory manager probably enforces some lock anyway when creating a new class but I want to ignore that for the moment. Edit: It may not have been clear from the above: For the full lifetime of the TDataManager object there is only one thread that writes to the data, not several that might compete for write access. So this is a special case of MREW.

  Read the article

• Why lock statements don't scale

  - by Alex.Davies

  We are going to have to stop using lock statements one day. Just like we had to stop using goto statements. The problem is similar, they're pretty easy to follow in small programs, but code with locks isn't composable. That means that small pieces of program that work in isolation can't necessarily be put together and work together. Of course actors scale fine :) Why lock statements don't scale as software gets bigger Deadlocks. You have a program with lots of threads picking up lots of locks. You already know that if two of your threads both try to pick up a lock that the other already has, they will deadlock. Your program will come to a grinding halt, and there will be fire and brimstone. "Easy!" you say, "Just make sure all the threads pick up the locks in the same order." Yes, that works. But you've broken composability. Now, to add a new lock to your code, you have to consider all the other locks already in your code and check that they are taken in the right order. Algorithm buffs will have noticed this approach means it takes quadratic time to write a program. That's bad. Why lock statements don't scale as hardware gets bigger Memory bus contention There's another headache, one that most programmers don't usually need to think about, but is going to bite us in a big way in a few years. Locking needs exclusive use of the entire system's memory bus while taking out the lock. That's not too bad for a single or dual-core system, but already for quad-core systems it's a pretty large overhead. Have a look at this blog about the .NET 4 ThreadPool for some numbers and a weird analogy (see the author's comment). Not too bad yet, but I'm scared my 1000 core machine of the future is going to go slower than my machine today! I don't know the answer to this problem yet. Maybe some kind of per-core work queue system with hierarchical work stealing. Definitely hardware support. But what I do know is that using locks specifically prevents any solution to this. We should be abstracting our code away from the details of locks as soon as possible, so we can swap in whatever solution arrives when it does. NAct uses locks at the moment. But my advice is that you code using actors (which do scale well as software gets bigger). And when there's a better way of implementing actors that'll scale well as hardware gets bigger, only NAct needs to work out how to use it, and your program will go fast on it's own.

  Read the article

• (Google AppEngine) Memcache Lock Entry

  - by Friedrich

  Hi, i need a locking in memcache. Since all operations are atomic that should be an easy task. My idea is to use a basic spin-lock mechanism. So every object that needs locking in memcache gets a lock object, which will be polled for access. // pseudo code // try to get a lock int lock; do { lock = Memcache.increment("lock", 1); } while(lock != 1) // ok we got the lock // do something here // and finally unlock Memcache.put("lock", 0); How does such a solution perform? Do you have a better idea how to lock a memcache object? Best regards, Friedrich Schick

  Read the article

• Python Locking Implementation (with threading module)

  - by Matty

  This is probably a rudimentary question, but I'm new to threaded programming in Python and am not entirely sure what the correct practice is. Should I be creating a single lock object (either globally or being passed around) and using that everywhere that I need to do locking? Or, should I be creating multiple lock instances in each of the classes where I will be employing them. Take these 2 rudimentary code samples, which direction is best to go? The main difference being that a single lock instance is used in both class A and B in the second, while multiple instances are used in the first. Sample 1 class A(): def __init__(self, theList): self.theList = theList self.lock = threading.Lock() def poll(self): while True: # do some stuff that eventually needs to work with theList self.lock.acquire() try: self.theList.append(something) finally: self.lock.release() class B(threading.Thread): def __init__(self,theList): self.theList = theList self.lock = threading.Lock() self.start() def run(self): while True: # do some stuff that eventually needs to work with theList self.lock.acquire() try: self.theList.remove(something) finally: self.lock.release() if __name__ == "__main__": aList = [] for x in range(10): B(aList) A(aList).poll() Sample 2 class A(): def __init__(self, theList,lock): self.theList = theList self.lock = lock def poll(self): while True: # do some stuff that eventually needs to work with theList self.lock.acquire() try: self.theList.append(something) finally: self.lock.release() class B(threading.Thread): def __init__(self,theList,lock): self.theList = theList self.lock = lock self.start() def run(self): while True: # do some stuff that eventually needs to work with theList self.lock.acquire() try: self.theList.remove(something) finally: self.lock.release() if __name__ == "__main__": lock = threading.Lock() aList = [] for x in range(10): B(aList,lock) A(aList,lock).poll()

  Read the article

• Java synchronized method lock on object, or method?

  - by wuntee

  If I have 2 synchronized methods in the same class, but each accessing different variables, can 2 threads access those 2 methods at the same time? Does the lock occur on the object, or does it get as specific as the variables inside the synchronized method? Example: class x{ private int a; private int b; public synchronized void addA(){ a++; } public synchronized void addB(){ b++; } } Can 2 threads access the same instance of class x performing x.addA() and x.addB() at the same time?

  Read the article

• How can I lock screen on lxde

  - by maniat1k

  Like gnome Control + alt + L In Lxde how can i do that? What I have to intall to do this? thanks --searching for a solution on my own but... ok if I do alt+f2 and type xscreensaver-command -lock that's a small solution. tryed to do an small script but it's not working.. this is what I do vi lock.sh #!/bin/bash xscreensaver-command -lock exit 0 chmod +x lock.sh but this doesnt work.. ideas?

  Read the article

• /var/lib/dpkg/lock.....help!

  - by Pycnopodia

  I had to reinstall the entire OS a little while ago and I have been trying to reinstall all of the programs I had before but I got a bit a of a problem now. I was trying to download dropbox from synaptic but it cannot finish the process and as a result I cannot update anything anymore. The line that comes out is: E: Could not get lock /var/lib/dpkg/lock - open (11: Resource temporarily unavailable) E: Unable to lock the administration directory (/var/lib/dpkg/), is another process using it? I have tried: sudo apt-get install -f sudo apt-get -f install sudo rm /var/lib/dpkg/lock sudo apt-get -f update sudo dpkg --clear-selections sudo dpkg --configure -a But nothing seems to work. So is there a way to solve this?? Thanks

  Read the article

• Figuring out the resource a lock in SQL Server 2000 affects

  - by Michael Lang

  I am adding a simple web-interface to show data from a commercial off the shelf (COTS) application. This COTS issues locks on any record the user is actively looking at (whether they intend to edit and update it or not). I have found sp_lock and the Microsoft sp_lock2 scripts and can see the locks, so that's all well and good. However, I cannot figure out how I can tell if a specific record I am about to update has been affected by one of these locks. If I submit the update request and there is in fact a lock, the web-interface will wait indefinitely until the user closes the window in the COTS. How can I either: a) determine before issuing an update that the record has been locked OR b) issue an update that will immediately return with a LOCKED status rather than indefinitely waiting on the COTS user to close their window on that record?

  Read the article

< Previous Page | 1 2 3 4 5 6 7 8 9 10 11 12  | Next Page >