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  • ubuntu: sem_timedwait not waking (C)

    - by gillez
    I have 3 processes which need to be synchronized. Process one does something then wakes process two and sleeps, which does something then wakes process three and sleeps, which does something and wakes process one and sleeps. The whole loop is timed to run around 25hz (caused by an external sync into process one before it triggers process two in my "real" application). I use sem_post to trigger (wake) each process, and sem_timedwait() to wait for the trigger. This all works successfully for several hours. However at some random time (usually after somewhere between two and four hours), one of the processes starts timing out in sem_timedwait(), even though I am sure the semaphore is being triggered with sem_post(). To prove this I even use sem_getvalue() immediately after the timeout, and the value is 1, so the timedwait should have been triggered. Please see following code: #include <stdio.h> #include <time.h> #include <string.h> #include <errno.h> #include <semaphore.h> sem_t trigger_sem1, trigger_sem2, trigger_sem3; // The main thread process. Called three times with a different num arg - 1, 2 or 3. void *thread(void *arg) { int num = (int) arg; sem_t *wait, *trigger; int val, retval; struct timespec ts; struct timeval tv; switch (num) { case 1: wait = &trigger_sem1; trigger = &trigger_sem2; break; case 2: wait = &trigger_sem2; trigger = &trigger_sem3; break; case 3: wait = &trigger_sem3; trigger = &trigger_sem1; break; } while (1) { // The first thread delays by 40ms to time the whole loop. // This is an external sync in the real app. if (num == 1) usleep(40000); // print sem value before we wait. If this is 1, sem_timedwait() will // return immediately, otherwise it will block until sem_post() is called on this sem. sem_getvalue(wait, &val); printf("sem%d wait sync sem%d. val before %d\n", num, num, val); // get current time and add half a second for timeout. gettimeofday(&tv, NULL); ts.tv_sec = tv.tv_sec; ts.tv_nsec = (tv.tv_usec + 500000); // add half a second if (ts.tv_nsec > 1000000) { ts.tv_sec++; ts.tv_nsec -= 1000000; } ts.tv_nsec *= 1000; /* convert to nanosecs */ retval = sem_timedwait(wait, &ts); if (retval == -1) { // timed out. Print value of sem now. This should be 0, otherwise sem_timedwait // would have woken before timeout (unless the sem_post happened between the // timeout and this call to sem_getvalue). sem_getvalue(wait, &val); printf("!!!!!! sem%d sem_timedwait failed: %s, val now %d\n", num, strerror(errno), val); } else printf("sem%d wakeup.\n", num); // get value of semaphore to trigger. If it's 1, don't post as it has already been // triggered and sem_timedwait on this sem *should* not block. sem_getvalue(trigger, &val); if (val <= 0) { printf("sem%d send sync sem%d. val before %d\n", num, (num == 3 ? 1 : num+1), val); sem_post(trigger); } else printf("!! sem%d not sending sync, val %d\n", num, val); } } int main(int argc, char *argv[]) { pthread_t t1, t2, t3; // create semaphores. val of sem1 is 1 to trigger straight away and start the whole ball rolling. if (sem_init(&trigger_sem1, 0, 1) == -1) perror("Error creating trigger_listman semaphore"); if (sem_init(&trigger_sem2, 0, 0) == -1) perror("Error creating trigger_comms semaphore"); if (sem_init(&trigger_sem3, 0, 0) == -1) perror("Error creating trigger_vws semaphore"); pthread_create(&t1, NULL, thread, (void *) 1); pthread_create(&t2, NULL, thread, (void *) 2); pthread_create(&t3, NULL, thread, (void *) 3); pthread_join(t1, NULL); pthread_join(t2, NULL); pthread_join(t3, NULL); } The following output is printed when the program is running correctly (at the start and for a random but long time after). The value of sem1 is always 1 before thread1 waits as it sleeps for 40ms, by which time sem3 has triggered it, so it wakes straight away. The other two threads wait until the semaphore is received from the previous thread. [...] sem1 wait sync sem1. val before 1 sem1 wakeup. sem1 send sync sem2. val before 0 sem2 wakeup. sem2 send sync sem3. val before 0 sem2 wait sync sem2. val before 0 sem3 wakeup. sem3 send sync sem1. val before 0 sem3 wait sync sem3. val before 0 sem1 wait sync sem1. val before 1 sem1 wakeup. sem1 send sync sem2. val before 0 [...] However, after a few hours, one of the threads begins to timeout. I can see from the output that the semaphore is being triggered, and when I print the value after the timeout is is 1. So sem_timedwait should have woken up well before the timeout. I would never expect the value of the semaphore to be 1 after the timeout, save for the very rare occasion (almost certainly never but it's possible) when the trigger happens after the timeout but before I call sem_getvalue. Also, once it begins to fail, every sem_timedwait() on that semaphore also fails in the same way. See the following output, which I've line-numbered: 01 sem3 wait sync sem3. val before 0 02 sem1 wakeup. 03 sem1 send sync sem2. val before 0 04 sem2 wakeup. 05 sem2 send sync sem3. val before 0 06 sem2 wait sync sem2. val before 0 07 sem1 wait sync sem1. val before 0 08 !!!!!! sem3 sem_timedwait failed: Connection timed out, val now 1 09 sem3 send sync sem1. val before 0 10 sem3 wait sync sem3. val before 1 11 sem3 wakeup. 12 !! sem3 not sending sync, val 1 13 sem3 wait sync sem3. val before 0 14 sem1 wakeup. [...] On line 1, thread 3 (which I have confusingly called sem1 in the printf) waits for sem3 to be triggered. On line 5, sem2 calls sem_post for sem3. However, line 8 shows sem3 timing out, but the value of the semaphore is 1. thread3 then triggers sem1 and waits again (10). However, because the value is already 1, it wakes straight away. It doesn't send sem1 again as this has all happened before control is given to thread1, however it then waits again (val is now 0) and sem1 wakes up. This now repeats for ever, sem3 always timing out and showing that the value is 1. So, my question is why does sem3 timeout, even though the semaphore has been triggered and the value is clearly 1? I would never expect to see line 08 in the output. If it times out (because, say thread 2 has crashed or is taking too long), the value should be 0. And why does it work fine for 3 or 4 hours first before getting into this state? This is using Ubuntu 9.4 with kernel 2.6.28. The same procedure has been working properly on Redhat and Fedora. But I'm now trying to port to ubuntu! Thanks for any advice, Giles

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  • Any script or command line tool that will allow me to sync a local folder with webdav?

    - by daniels
    I have a local folder on my mac that I want to sync with a webdav server. There are a lot of files in my folder and I would need that after I edit some files or add/remove folder to be able to sync the changes to the webdav server ignoring what it is on the server and always using my files. Is there any script or tool that I can use from command line to do that? And mounting the resource is not a solution.

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  • How to sync an Android phone with anything other than Google?

    - by Francisco Canedo
    As I understand, the Android phone can only sync with Google (GMail, Google Calendar, etc.) out of the box. I can imagine corporate users having a problem with their data residing on Google's servers — despite their "do no evil" credo. Is there any Android application that lets you sync with the desktop (either Linux or Windows) or corporate server applications (think Exchange)?

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  • Is there an application or way to sync address book, Facebook, LinkedIn, Gmail contacts?

    - by denislexic
    I'm looking for a Mac application or an Web application to sync all my Facebook, LinkedIn, Gmail contacts and Mac OS X address book contacts in one place. At the same time, it would be great if it didn't create a bunch of duplicates. (PS: The default sync between gmail contacts and address book seems to only create duplicates and doesn't seem to really work well together). Does anyone have a solution?

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  • Cron job running successfully suddenly reports script is not found

    - by Ted B
    What might cause cron to suddenly report a file it is supposed to run is "not found," when the file hasn't been touched, and in fact, the entire system hasn't been touched since it last ran successfully? I have a cronjob schedule I define by doing sudo crontab -e In it, I have dozens of cron jobs that run successfully.. I do not have a PATH specified, and I use absolute paths to call all my scheduled scripts, setting the PATH in them as needed. I do not specify a SHELL in the crontab. All scripts identify the shell as their first line. Without me touching the system, a particular job defined in the middle of other jobs will suddenly stop running. To debug this, I added an output redirection to a log file. In that, the output clearly shows the output of the script successfully running time after time for weeks, and then suddenly the following appears: /bin/sh: /home/iupress/bin/sync-email_images: not found /bin/sh: /home/iupress/bin/sync-email_images: not found /bin/sh: /home/iupress/bin/sync-email_images: not found /bin/sh: /home/iupress/bin/sync-email_images: not found /bin/sh: /home/iupress/bin/sync-email_images: not found /bin/sh: /home/iupress/bin/sync-email_images: not found /bin/sh: /home/iupress/bin/sync-email_images: not found /bin/sh: /home/iupress/bin/sync-email_images: not found /bin/sh: /home/iupress/bin/sync-email_images: not found If I do the ls command, copying and pasting that exact path from the error message, it clearly reports the file is still there (no surprise). Yet the log continues to report that file is "not found" until I take action. I can run the script manually and it runs just fine. If I do sudo crontab -e and save the file, the job runs on the next scheduled time, putting its output in the log, no longer reporting the script is "not found". It seems to me the contents of the script trying to be run are irrelevant since cron doesn't even process the file because it is "not found". I have a job scheduled below the one that is encountering this problem that I know is continuing to run, because I have its output mailed to me. So I know cron is running and continues to run at least one other job, even after it suddenly reports this job's script is "not found". All my lines end with a newline. I had no periods in the crontab until I added the redirection to a log file. I have now added a PATH specification, but left the absolute paths in the jobs. Unfortunately, I have no idea if and when this problem will occur. It will likely be weeks from now. By the way, I am running a script to syncronize the clock, and I see the time is exactly what it should be.

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  • Why not sync folders outside home with ubuntu-one?

    - by peer
    It took me a while to find out that with ubuntu-one I can sync only folders in my home-folder. On all other folders the ubuntu-one - option is available in preferences, but the actual actions are greyed out. The ubuntu-faq is quite clear on that: https://wiki.ubuntu.com/UbuntuOne/FAQ/CanISyncAFolderOutsideMyHomeFolder But I actually wonder why and if this is going to change and if there is a trick around it (an other one than setting my home to /) I personally dont have any important data in my home-folder other than the program-configs. All documents, pictures, music are on a folder called /data that is actually on a different partition. That makes it much easier when one wants to reinstall ubuntu.

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  • Why not sync folders outside home with Ubuntu One?

    - by peer
    It took me a while to find out that with Ubuntu One I can sync only folders in my home folder. On all other folders the Ubuntu One option is available in preferences, but the actual actions are greyed out. The Ubuntu One FAQ is quite clear on that: No, currently you can only select to synchronize folders inside your home directory. But I actually wonder why and if this is going to change and if there is a trick around it (an other one than setting my home to /) ? I personally don't have any important data in my home folder other than the program configs. All documents, pictures, music are on a folder called /data that is actually on a different partition. That makes it much easier when one wants to reinstall Ubuntu.

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  • background: why not sync folders outside home with ubuntu-one?

    - by peer
    It took me a while to find out that with ubuntu-one I can sync only folders in my home-folder. On all other folders the ubuntu-one - option is available in preferences, but the actual actions are greyed out. the ubuntu-faq is quite clear on that: https://wiki.ubuntu.com/UbuntuOne/FAQ/CanISyncAFolderOutsideMyHomeFolder But I actually wonder why and if this is going to change and if there is a trick around it (an other one than setting my home to / ;) ) I personally dont have any important data in my home-folder other than the program-configs. All documents, pictures, music are on a folder called /data that is actually on a different partition. That makes it much easier when one wants to reinstall ubuntu. thnx, p

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  • What is the correct term for - server/client database sync via API?

    - by Daniel
    Forgive the vague question title. I've been programming mobile apps for 3 years now, and I've got a little too far from the web services and server side code then I probably should have. Anyway, I'm doing a personal project now and I want to create an web API for it. One of my requirements is to check for updates from my app, so I would send a timestamp to the API. I've used many APIs that my clients prepared for me and only now am I appreciating their work ! What is the term or technique used to create an API backed by a database which tracks changes via dates/timestamps, basically an effective way for me to query changes occurring since a timestamp. Simply put, I want that my app can call my API in order to sync new data and changed data from the server, to the app. The app would only have a timestamp of the last time it synced with the server. Would I have a log table for each data table in my database which adds a record for each change? Then I could query all changes with a timestamp superior to the one passed to the API. Can anyone point me in the right direction on this?

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  • Google Contacts and Mac OS X Address Book

    - by dyve
    The sync that Google offers for Google Contacts < Mac OS X Address Book is seriously flawed. It doesn't sync automatically, it doesn't sync all contacts, it doesn't sync all fields. See here for a list of warnings and issues. Is there a better way to sync Google Contacts to Mac Address Book bidirectionally? Preferably free, and preferably without adding extra software. I have tried to do it through Plaxo (which has an excellent Mac Address Book sync, albeit through an extra software install), but Plaxo doesn't handle Google Sync well (no updates). UPDATE: For the new Mac OS X Snow Leopard this shouldn't be an issue. This question is looking for a Leopard answer.

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  • Tool to fix video that's out of sync with audio?

    - by Javier Badia
    I'm looking for (preferably free) software for Windows 7 that will allow me to fix an AVI file that has audio out of sync with the video. I tried with Windows Live Movie Maker and VirtualDub and couldn't find out how to do it (if at all possible) on both of them. If any of those can help me, instructions for that would also be nice. Background: I have a RCA-to-USB capture card, which I'm using to transfer VHS casettes and stuff from a video camera to digital format. The problem is that the audio comes out heavily distorted. So instead I connected the audio out from the VCR directly to the computer's line in. This works, but the audio is out of sync, about half a second behind the video. I could spend time trying to fix this issuee, but I think it'll be easier to simply fix the video.

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  • Dropbox takes hours? to sync & shows diff. modified times (coincidentially in the future)

    - by user10580
    Dropbox is taking hours to sync, I can't tell exactly how long because the time stamps on the website make no sense - they say the files were modified. . . tomorrow. Actually my netbook (windows xp) says they're last modified tomorrow in windows explorer as well. It's bizarre. The time and date on both computers are correct. The files in question are in a symlinked directory on the laptop (which are synced fine, with the correct timestamps). I have looked for an option to force dropbox to sync, but haven't located one. (There might be a command line method, but I haven't had the time to explore). thanks

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  • What is the functionality of "sync contacts" in Exchange account in Email application?

    - by santhosh
    Hi i am testing android E-mail application . I have configured an Exchange account where in i could find an option "Sync Contacts from this account" in Account settings. According to my understanding if i check "sync contacts from the account" option , i must be able to access contacts in the exchange account i have configured. But i don't know how to get/access these contacts in android email application. Can any one who have used this functionality or know about it can suggest to me how to make use of "Sync contacts" functionality. Or if you have any idea about, how i can test this functionality, i am very eager to here to you. Kinds & Regards Santhosh Kumar H.E

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  • How to sync bookmarks between Firefox, Chrome, and Safari on multiple computers?

    - by Tai Squared
    There are some similar question on bookmark syncing, but most answers point to Delicious or Google bookmarks. However, as Chrome doesn't have the Google toolbar, how would those sync? I use several computers and different browsers on them so I would like a easy solution to keep all of the bookmarks in sync on various computers and browsers in the same organizational structure throughout. Also, I would prefer to have my bookmarks only synced to my account, not necessarily visible to the whole world as on Delicious. Is there any service that could handle this?

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  • Is it possible to sync specific router settings across multiple routers?

    - by Betard Fooser
    I recently purchased a second Linksys wireless routers set up on the other side of my home and I am wondering if it is possible to somehow sync particular settings between the two? For instance what I am really after is the "MAC Filter List". I would "like" to be able to maintain the list on both routers without having to manually type in the field values. maybe this isn't possible, or has an easy answer, but hopefully those of you who know will cut me a bit of slack. I tried to "google" the answer to this of course, but it seems any searches with the words "sync" and "router" and/or "wifi" result in pages of people having issues with synching their iOS devices over wifi. I would say that have decent amount of networking knowledge in regards to average home networks, and I imagine in larger businesses / corporations they must have a "simpler" way of maintaining things like this. Any insight to point me in the right direction will be much appreciated.

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  • Service or software to auto-sync one server to another so they are identical?

    - by Ryan
    We have a main node in a DC data center and want to setup a back-up node in Seattle. The back-up node will only be used if the DC node goes down and we switch it over while DC node is repaired. The question is, what kind of services out there allow me to sync the data, I suppose we want to do it fairly frequently so if something goes down there isn't much loss in data between the time of failure and the last back-up/sync. Is there any common solution for this? It's Windows Server 2003 running Parallels Virtuozzo.

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  • Use a media player in Linux just to play files from an iPod device (no sync, no manage, just play)?

    - by Somebody still uses you MS-DOS
    I have an ipod classic 160gb, that I sync with my machine at home. I use Linux at work, and want to just plug my ipod and just listen to the tracks, with all the playlists and such. I don't want to sync nothing, I just want to listen to the tracks as if I was using the ipod itself. Why? Because this way I can use the usb port. So, I don't want to manage my ipod in Linux, I just want to listen to the tracks on it in Linux, like it was a local library but it's instead in my ipod. (I've tried gtkpod, it works to show my files, but I can't play, shuffle, etc. It would be interesting to have a complete audio software to handle everything like it was a local library)

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  • How to sync apps with one Mac and 3 devices?

    - by openfrog
    We have 1 Mac, with 1 iTunes account, and 3 iOS devices. Every time we sync one device, iTunes either spams it with ALL apps from ALL devices, OR it removes all of the apps from the device including all the data. Which is very annoying. Someone told me there is a way to tell iTunes to keep separate track of the devices. How can I setup iTunes such that it will not transfer all my iPhone-only apps to my iPad every time I sync? Basically I want the devices to be the "master". They give the direction which apps should be on the device, and not the other way around.

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  • How do I sync a subset of tables between two databases on the same mysql database server

    - by Mike
    would like to be able to sync a subset of tables between two mysql databases that are running on the same server. One of the databases acts as the master where inserts, updates and deletes can be made. The second database uses those same tables for read-only operations. I do not want to use federated tables to achieve this. The long term goal will be to separate the 2 databases to multiple servers, The second database that has the subset of tables as read-only may also be replicated a few times over to distribute geographically for load and performance purposes each with unqiue data.... Once that is achieved, I plan to use binlog to replicate those specific tables on the secondary databases. In the meantime, I'd like to keep these tables in sync. Is there a more elegant way to do this than other than using a cronjob and mysqldump?

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  • What is the best way to sync multiple client SqlServers to one MS SqlServer 2005?

    - by user605055
    I have several client databases that use my windows application. I want to send this data for online web site. The client databases and server database structure is different because we need to add client ID column to some tables in server data base. I use this way to sync databases; use another application and use C# bulk copy with transaction to sync databases. My server database sql server is too busy and parallel task cannot be run. I work on this solution: I use triggers after update, delete, insert to save changes in one table and create sql query to send a web service to sync data. But I must send all data first! Huge data set (bigger than 16mg) I think can't use replication because the structure and primary keys are different.

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