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• C++: static function member shared between threads, can block all?

  - by mhambra

  Hi all, I have a class, which has static function defined to work with C-style extern C { static void callback(foo bar) { } }. // static is defined in header. Three objects (each in separate pthread) are instantiated from this class, each of them has own loop (in class constructor), which can receive the callback. The pointer to function is passed as: x = init_function(h, queue_id, &callback, NULL); while(1) { loop_function(x); } So each thread has the same pointer to &callback. Callback function can block for minutes. Each thread object, excluding the one which got the blocking callback, can call callback again. If the callback function exists only once, then any thread attempting to callback will also block. This would give me an undesired bug, circa is interesting to ask: can anything in C++ become acting this way? Maybe, due to extern { } or some pointer usage?

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• Issues with time slicing

  - by user12331

  I was trying to see the effect of time slicing. And how it can consume significant amount of time. Actually, I was trying to divide a certain work into number of threads and see the effect. I have a two core processor. So two threads can run in parallel. I was trying to see if I have a work w that is done by 2 threads, and if I have the same work done by t threads with each thread doing w/t of the work. How much does time slicing play a role in it As time slicing is time consuming process, I was expecting that when I do the same work using a two thread process or by a t thread process, the amount of time taken by the t thread process will be more Any suggestions?

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• Scaling a ruby script by launching multiple processes instead of using threads.

  - by Zombies

  I want to increase the throughput of a script which does net I/O (a scraper). Instead of making it multithreaded in ruby (I use the default 1.9.1 interpreter), I want to launch multiple processes. So, is there a system for doing this to where I can track when one finishes to re-launch it again so that I have X number running at any time. ALso some will run with different command args. I was thinking of writing a bash script but it sounds like a potentially bad idea if there already exists a method for doing something like this on linux.

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• How do I read and write to a file using threads in java?

  - by WarmWaffles

  I'm writing an application where I need to read blocks in from a single file, each block is roughly 512 bytes. I am also needing to write blocks simultaneously. One of the ideas I had was BlockReader implements Runnable and BlockWriter implements Runnable and BlockManager manages both the reader and writer. The problem that I am seeing with most examples that I have found was locking problems and potential deadlock situations. Any ideas how to implement this?

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• Reading from a very large table using multiple threads (Java ) and writing them to a single file

  - by user2534926

  I am currently facing a situation where i have a table with almost 80 millions data and i have to take a dump of that table and store it into a csv file. Currently i am using a not so professional approach( with a perl script+DBI interface , printing the values to stdout and redirecting to a csv file). Now i am planning to use java threading approach. Can you suggest a way forward. Thanks in advance

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• Did I lose my RAID again?

  - by BarsMonster

  Hi! A little history: 2 years ago I was really excited to find out that mdadm is so powerful that it even can reshape arrays, so you can start with a smaller array and then grow it as you need. I've bought 3x1Tb drives and made a RAID-5. It was fine for a year. Then I bought 2x more, and tried to reshape to RAID-6 out of 5 drives, and due to some mess with superblock versions, lost all content. Had to rebuild it from scratch, but 2Tb of data were gone. Yesterday I bought 2 more drives, and this time I had everything: properly built array, UPS. I've disabled write intent map, added 2 new drives as spares and run a command to grow array to 7-disks. It started working, but speed was ridiculously slow, ~100kb/sec. After processing first 37Mb at such an amazing speed, one of old HDDs fails. I properly shutdown the PC and disconnected the failed drive. After bootup it appeared that it recreated the intent map as it was still in mdadm config, so I removed it from config and rebooted again. Now all I see is that all mdadm processes deadlock, and don't do anything. PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 1937 root 20 0 12992 608 444 D 0 0.1 0:00.00 mdadm 2283 root 20 0 12992 852 704 D 0 0.1 0:00.01 mdadm 2287 root 20 0 0 0 0 D 0 0.0 0:00.01 md0_reshape 2288 root 18 -2 12992 820 676 D 0 0.1 0:00.01 mdadm And all I see in mdstat is: $ cat /proc/mdstat Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] md0 : active raid6 sdb1[1] sdg1[4] sdf1[7] sde1[6] sdd1[0] sdc1[5] 2929683456 blocks super 1.2 level 6, 1024k chunk, algorithm 2 [7/6] [UU_UUUU] [>....................] reshape = 0.0% (37888/976561152) finish=567604147.2min speed=0K/sec I've already tried mdadm 2.6.7, 3.1.4 and 3.2 - nothing helps. Did I lose my data again? Any suggestions on how can I make this work? OS is Ubuntu Server 10.04.2. PS. Needless to say, the data is inaccessible - I cannot mount /dev/md0 to save the most valuable data. You can see my disappointment - the very specific thing I was excited about failed twice taking 5Tb of my data with it. Update: It appears there is some nice info in kern.log: 21:38:48 ...: [ 166.522055] raid5: reshape will continue 21:38:48 ...: [ 166.522085] raid5: device sdb1 operational as raid disk 1 21:38:48 ...: [ 166.522091] raid5: device sdg1 operational as raid disk 4 21:38:48 ...: [ 166.522097] raid5: device sdf1 operational as raid disk 5 21:38:48 ...: [ 166.522102] raid5: device sde1 operational as raid disk 6 21:38:48 ...: [ 166.522107] raid5: device sdd1 operational as raid disk 0 21:38:48 ...: [ 166.522111] raid5: device sdc1 operational as raid disk 3 21:38:48 ...: [ 166.523942] raid5: allocated 7438kB for md0 21:38:48 ...: [ 166.524041] 1: w=1 pa=2 pr=5 m=2 a=2 r=7 op1=0 op2=0 21:38:48 ...: [ 166.524050] 4: w=2 pa=2 pr=5 m=2 a=2 r=7 op1=0 op2=0 21:38:48 ...: [ 166.524056] 5: w=3 pa=2 pr=5 m=2 a=2 r=7 op1=0 op2=0 21:38:48 ...: [ 166.524062] 6: w=4 pa=2 pr=5 m=2 a=2 r=7 op1=0 op2=0 21:38:48 ...: [ 166.524068] 0: w=5 pa=2 pr=5 m=2 a=2 r=7 op1=0 op2=0 21:38:48 ...: [ 166.524073] 3: w=6 pa=2 pr=5 m=2 a=2 r=7 op1=0 op2=0 21:38:48 ...: [ 166.524079] raid5: raid level 6 set md0 active with 6 out of 7 devices, algorithm 2 21:38:48 ...: [ 166.524519] RAID5 conf printout: 21:38:48 ...: [ 166.524523] --- rd:7 wd:6 21:38:48 ...: [ 166.524528] disk 0, o:1, dev:sdd1 21:38:48 ...: [ 166.524532] disk 1, o:1, dev:sdb1 21:38:48 ...: [ 166.524537] disk 3, o:1, dev:sdc1 21:38:48 ...: [ 166.524541] disk 4, o:1, dev:sdg1 21:38:48 ...: [ 166.524545] disk 5, o:1, dev:sdf1 21:38:48 ...: [ 166.524550] disk 6, o:1, dev:sde1 21:38:48 ...: [ 166.524553] ...ok start reshape thread 21:38:48 ...: [ 166.524727] md0: detected capacity change from 0 to 2999995858944 21:38:48 ...: [ 166.524735] md: reshape of RAID array md0 21:38:48 ...: [ 166.524740] md: minimum _guaranteed_ speed: 1000 KB/sec/disk. 21:38:48 ...: [ 166.524745] md: using maximum available idle IO bandwidth (but not more than 200000 KB/sec) for reshape. 21:38:48 ...: [ 166.524756] md: using 128k window, over a total of 976561152 blocks. 21:39:05 ...: [ 166.525013] md0: 21:42:04 ...: [ 362.520063] INFO: task mdadm:1937 blocked for more than 120 seconds. 21:42:04 ...: [ 362.520068] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. 21:42:04 ...: [ 362.520073] mdadm D 00000000ffffffff 0 1937 1 0x00000000 21:42:04 ...: [ 362.520083] ffff88002ef4f5d8 0000000000000082 0000000000015bc0 0000000000015bc0 21:42:04 ...: [ 362.520092] ffff88002eb5b198 ffff88002ef4ffd8 0000000000015bc0 ffff88002eb5ade0 21:42:04 ...: [ 362.520100] 0000000000015bc0 ffff88002ef4ffd8 0000000000015bc0 ffff88002eb5b198 21:42:04 ...: [ 362.520107] Call Trace: 21:42:04 ...: [ 362.520133] [<ffffffffa0224892>] get_active_stripe+0x312/0x3f0 [raid456] 21:42:04 ...: [ 362.520148] [<ffffffff81059ae0>] ? default_wake_function+0x0/0x20 21:42:04 ...: [ 362.520159] [<ffffffffa0228413>] make_request+0x243/0x4b0 [raid456] 21:42:04 ...: [ 362.520169] [<ffffffffa0221a90>] ? release_stripe+0x50/0x70 [raid456] 21:42:04 ...: [ 362.520179] [<ffffffff81084790>] ? autoremove_wake_function+0x0/0x40 21:42:04 ...: [ 362.520188] [<ffffffff81414df0>] md_make_request+0xc0/0x130 21:42:04 ...: [ 362.520194] [<ffffffff81414df0>] ? md_make_request+0xc0/0x130 21:42:04 ...: [ 362.520205] [<ffffffff8129f8c1>] generic_make_request+0x1b1/0x4f0 21:42:04 ...: [ 362.520214] [<ffffffff810f6515>] ? mempool_alloc_slab+0x15/0x20 21:42:04 ...: [ 362.520222] [<ffffffff8116c2ec>] ? alloc_buffer_head+0x1c/0x60 21:42:04 ...: [ 362.520230] [<ffffffff8129fc80>] submit_bio+0x80/0x110 21:42:04 ...: [ 362.520236] [<ffffffff8116c849>] submit_bh+0xf9/0x140 21:42:04 ...: [ 362.520244] [<ffffffff8116f124>] block_read_full_page+0x274/0x3b0 21:42:04 ...: [ 362.520251] [<ffffffff81172c90>] ? blkdev_get_block+0x0/0x70 21:42:04 ...: [ 362.520258] [<ffffffff8110d875>] ? __inc_zone_page_state+0x35/0x40 21:42:04 ...: [ 362.520265] [<ffffffff810f46d8>] ? add_to_page_cache_locked+0xe8/0x160 21:42:04 ...: [ 362.520272] [<ffffffff81173d78>] blkdev_readpage+0x18/0x20 21:42:04 ...: [ 362.520279] [<ffffffff810f484b>] __read_cache_page+0x7b/0xe0 21:42:04 ...: [ 362.520285] [<ffffffff81173d60>] ? blkdev_readpage+0x0/0x20 21:42:04 ...: [ 362.520290] [<ffffffff81173d60>] ? blkdev_readpage+0x0/0x20 21:42:04 ...: [ 362.520297] [<ffffffff810f57dc>] do_read_cache_page+0x3c/0x120 21:42:04 ...: [ 362.520304] [<ffffffff810f5909>] read_cache_page_async+0x19/0x20 21:42:04 ...: [ 362.520310] [<ffffffff810f591e>] read_cache_page+0xe/0x20 21:42:04 ...: [ 362.520317] [<ffffffff811a6cb0>] read_dev_sector+0x30/0xa0 21:42:04 ...: [ 362.520324] [<ffffffff811a7fcd>] amiga_partition+0x6d/0x460 21:42:04 ...: [ 362.520331] [<ffffffff811a7938>] check_partition+0x138/0x190 21:42:04 ...: [ 362.520338] [<ffffffff811a7a7a>] rescan_partitions+0xea/0x2f0 21:42:04 ...: [ 362.520344] [<ffffffff811744c7>] __blkdev_get+0x267/0x3d0 21:42:04 ...: [ 362.520350] [<ffffffff81174650>] ? blkdev_open+0x0/0xc0 21:42:04 ...: [ 362.520356] [<ffffffff81174640>] blkdev_get+0x10/0x20 21:42:04 ...: [ 362.520362] [<ffffffff811746c1>] blkdev_open+0x71/0xc0 21:42:04 ...: [ 362.520369] [<ffffffff811419f3>] __dentry_open+0x113/0x370 21:42:04 ...: [ 362.520377] [<ffffffff81253f8f>] ? security_inode_permission+0x1f/0x30 21:42:04 ...: [ 362.520385] [<ffffffff8114de3f>] ? inode_permission+0xaf/0xd0 21:42:04 ...: [ 362.520391] [<ffffffff81141d67>] nameidata_to_filp+0x57/0x70 21:42:04 ...: [ 362.520398] [<ffffffff8115207a>] do_filp_open+0x2da/0xba0 21:42:04 ...: [ 362.520406] [<ffffffff811134a8>] ? unmap_vmas+0x178/0x310 21:42:04 ...: [ 362.520414] [<ffffffff8115dbfa>] ? alloc_fd+0x10a/0x150 21:42:04 ...: [ 362.520421] [<ffffffff81141769>] do_sys_open+0x69/0x170 21:42:04 ...: [ 362.520428] [<ffffffff811418b0>] sys_open+0x20/0x30 21:42:04 ...: [ 362.520437] [<ffffffff810121b2>] system_call_fastpath+0x16/0x1b 21:42:04 ...: [ 362.520446] INFO: task mdadm:2283 blocked for more than 120 seconds. 21:42:04 ...: [ 362.520450] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. 21:42:04 ...: [ 362.520454] mdadm D 0000000000000000 0 2283 2212 0x00000000 21:42:04 ...: [ 362.520462] ffff88002cca7d98 0000000000000086 0000000000015bc0 0000000000015bc0 21:42:04 ...: [ 362.520470] ffff88002ededf78 ffff88002cca7fd8 0000000000015bc0 ffff88002ededbc0 21:42:04 ...: [ 362.520478] 0000000000015bc0 ffff88002cca7fd8 0000000000015bc0 ffff88002ededf78 21:42:04 ...: [ 362.520485] Call Trace: 21:42:04 ...: [ 362.520495] [<ffffffff81543a97>] __mutex_lock_slowpath+0xf7/0x180 21:42:04 ...: [ 362.520502] [<ffffffff8154397b>] mutex_lock+0x2b/0x50 21:42:04 ...: [ 362.520508] [<ffffffff8117404d>] __blkdev_put+0x3d/0x190 21:42:04 ...: [ 362.520514] [<ffffffff811741b0>] blkdev_put+0x10/0x20 21:42:04 ...: [ 362.520520] [<ffffffff811741f3>] blkdev_close+0x33/0x60 21:42:04 ...: [ 362.520527] [<ffffffff81145375>] __fput+0xf5/0x210 21:42:04 ...: [ 362.520534] [<ffffffff811454b5>] fput+0x25/0x30 21:42:04 ...: [ 362.520540] [<ffffffff811415ad>] filp_close+0x5d/0x90 21:42:04 ...: [ 362.520546] [<ffffffff81141697>] sys_close+0xb7/0x120 21:42:04 ...: [ 362.520553] [<ffffffff810121b2>] system_call_fastpath+0x16/0x1b 21:42:04 ...: [ 362.520559] INFO: task md0_reshape:2287 blocked for more than 120 seconds. 21:42:04 ...: [ 362.520563] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. 21:42:04 ...: [ 362.520567] md0_reshape D ffff88003aee96f0 0 2287 2 0x00000000 21:42:04 ...: [ 362.520575] ffff88003cf05a70 0000000000000046 0000000000015bc0 0000000000015bc0 21:42:04 ...: [ 362.520582] ffff88003aee9aa8 ffff88003cf05fd8 0000000000015bc0 ffff88003aee96f0 21:42:04 ...: [ 362.520590] 0000000000015bc0 ffff88003cf05fd8 0000000000015bc0 ffff88003aee9aa8 21:42:04 ...: [ 362.520597] Call Trace: 21:42:04 ...: [ 362.520608] [<ffffffffa0224892>] get_active_stripe+0x312/0x3f0 [raid456] 21:42:04 ...: [ 362.520616] [<ffffffff81059ae0>] ? default_wake_function+0x0/0x20 21:42:04 ...: [ 362.520626] [<ffffffffa0226f80>] reshape_request+0x4c0/0x9a0 [raid456] 21:42:04 ...: [ 362.520634] [<ffffffff81084790>] ? autoremove_wake_function+0x0/0x40 21:42:04 ...: [ 362.520644] [<ffffffffa022777a>] sync_request+0x31a/0x3a0 [raid456] 21:42:04 ...: [ 362.520651] [<ffffffff81052713>] ? __wake_up+0x53/0x70 21:42:04 ...: [ 362.520658] [<ffffffff814156b1>] md_do_sync+0x621/0xbb0 21:42:04 ...: [ 362.520668] [<ffffffff810387b9>] ? default_spin_lock_flags+0x9/0x10 21:42:04 ...: [ 362.520675] [<ffffffff8141640c>] md_thread+0x5c/0x130 21:42:04 ...: [ 362.520681] [<ffffffff81084790>] ? autoremove_wake_function+0x0/0x40 21:42:04 ...: [ 362.520688] [<ffffffff814163b0>] ? md_thread+0x0/0x130 21:42:04 ...: [ 362.520694] [<ffffffff81084416>] kthread+0x96/0xa0 21:42:04 ...: [ 362.520701] [<ffffffff810131ea>] child_rip+0xa/0x20 21:42:04 ...: [ 362.520707] [<ffffffff81084380>] ? kthread+0x0/0xa0 21:42:04 ...: [ 362.520713] [<ffffffff810131e0>] ? child_rip+0x0/0x20 21:42:04 ...: [ 362.520718] INFO: task mdadm:2288 blocked for more than 120 seconds. 21:42:04 ...: [ 362.520721] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. 21:42:04 ...: [ 362.520725] mdadm D 0000000000000000 0 2288 1 0x00000000 21:42:04 ...: [ 362.520733] ffff88002cca9c18 0000000000000086 0000000000015bc0 0000000000015bc0 21:42:04 ...: [ 362.520741] ffff88003aee83b8 ffff88002cca9fd8 0000000000015bc0 ffff88003aee8000 21:42:04 ...: [ 362.520748] 0000000000015bc0 ffff88002cca9fd8 0000000000015bc0 ffff88003aee83b8 21:42:04 ...: [ 362.520755] Call Trace: 21:42:04 ...: [ 362.520763] [<ffffffff81543a97>] __mutex_lock_slowpath+0xf7/0x180 21:42:04 ...: [ 362.520771] [<ffffffff812a6d50>] ? exact_match+0x0/0x10 21:42:04 ...: [ 362.520777] [<ffffffff8154397b>] mutex_lock+0x2b/0x50 21:42:04 ...: [ 362.520783] [<ffffffff811742c8>] __blkdev_get+0x68/0x3d0 21:42:04 ...: [ 362.520790] [<ffffffff81174650>] ? blkdev_open+0x0/0xc0 21:42:04 ...: [ 362.520795] [<ffffffff81174640>] blkdev_get+0x10/0x20 21:42:04 ...: [ 362.520801] [<ffffffff811746c1>] blkdev_open+0x71/0xc0 21:42:04 ...: [ 362.520808] [<ffffffff811419f3>] __dentry_open+0x113/0x370 21:42:04 ...: [ 362.520815] [<ffffffff81253f8f>] ? security_inode_permission+0x1f/0x30 21:42:04 ...: [ 362.520821] [<ffffffff8114de3f>] ? inode_permission+0xaf/0xd0 21:42:04 ...: [ 362.520828] [<ffffffff81141d67>] nameidata_to_filp+0x57/0x70 21:42:04 ...: [ 362.520834] [<ffffffff8115207a>] do_filp_open+0x2da/0xba0 21:42:04 ...: [ 362.520841] [<ffffffff810ff0e1>] ? lru_cache_add_lru+0x21/0x40 21:42:04 ...: [ 362.520848] [<ffffffff8111109c>] ? do_anonymous_page+0x11c/0x330 21:42:04 ...: [ 362.520855] [<ffffffff81115d5f>] ? handle_mm_fault+0x31f/0x3c0 21:42:04 ...: [ 362.520862] [<ffffffff8115dbfa>] ? alloc_fd+0x10a/0x150 21:42:04 ...: [ 362.520868] [<ffffffff81141769>] do_sys_open+0x69/0x170 21:42:04 ...: [ 362.520874] [<ffffffff811418b0>] sys_open+0x20/0x30 21:42:04 ...: [ 362.520882] [<ffffffff810121b2>] system_call_fastpath+0x16/0x1b 21:44:04 ...: [ 482.520065] INFO: task mdadm:1937 blocked for more than 120 seconds. 21:44:04 ...: [ 482.520071] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. 21:44:04 ...: [ 482.520077] mdadm D 00000000ffffffff 0 1937 1 0x00000000 21:44:04 ...: [ 482.520087] ffff88002ef4f5d8 0000000000000082 0000000000015bc0 0000000000015bc0 21:44:04 ...: [ 482.520096] ffff88002eb5b198 ffff88002ef4ffd8 0000000000015bc0 ffff88002eb5ade0 21:44:04 ...: [ 482.520104] 0000000000015bc0 ffff88002ef4ffd8 0000000000015bc0 ffff88002eb5b198 21:44:04 ...: [ 482.520112] Call Trace: 21:44:04 ...: [ 482.520139] [<ffffffffa0224892>] get_active_stripe+0x312/0x3f0 [raid456] 21:44:04 ...: [ 482.520154] [<ffffffff81059ae0>] ? default_wake_function+0x0/0x20 21:44:04 ...: [ 482.520165] [<ffffffffa0228413>] make_request+0x243/0x4b0 [raid456] 21:44:04 ...: [ 482.520175] [<ffffffffa0221a90>] ? release_stripe+0x50/0x70 [raid456] 21:44:04 ...: [ 482.520185] [<ffffffff81084790>] ? autoremove_wake_function+0x0/0x40 21:44:04 ...: [ 482.520194] [<ffffffff81414df0>] md_make_request+0xc0/0x130 21:44:04 ...: [ 482.520201] [<ffffffff81414df0>] ? md_make_request+0xc0/0x130 21:44:04 ...: [ 482.520212] [<ffffffff8129f8c1>] generic_make_request+0x1b1/0x4f0 21:44:04 ...: [ 482.520221] [<ffffffff810f6515>] ? mempool_alloc_slab+0x15/0x20 21:44:04 ...: [ 482.520229] [<ffffffff8116c2ec>] ? alloc_buffer_head+0x1c/0x60 21:44:04 ...: [ 482.520237] [<ffffffff8129fc80>] submit_bio+0x80/0x110 21:44:04 ...: [ 482.520244] [<ffffffff8116c849>] submit_bh+0xf9/0x140 21:44:04 ...: [ 482.520252] [<ffffffff8116f124>] block_read_full_page+0x274/0x3b0 21:44:04 ...: [ 482.520258] [<ffffffff81172c90>] ? blkdev_get_block+0x0/0x70 21:44:04 ...: [ 482.520266] [<ffffffff8110d875>] ? __inc_zone_page_state+0x35/0x40 21:44:04 ...: [ 482.520273] [<ffffffff810f46d8>] ? add_to_page_cache_locked+0xe8/0x160 21:44:04 ...: [ 482.520280] [<ffffffff81173d78>] blkdev_readpage+0x18/0x20 21:44:04 ...: [ 482.520286] [<ffffffff810f484b>] __read_cache_page+0x7b/0xe0 21:44:04 ...: [ 482.520293] [<ffffffff81173d60>] ? blkdev_readpage+0x0/0x20 21:44:04 ...: [ 482.520299] [<ffffffff81173d60>] ? blkdev_readpage+0x0/0x20 21:44:04 ...: [ 482.520306] [<ffffffff810f57dc>] do_read_cache_page+0x3c/0x120 21:44:04 ...: [ 482.520313] [<ffffffff810f5909>] read_cache_page_async+0x19/0x20 21:44:04 ...: [ 482.520319] [<ffffffff810f591e>] read_cache_page+0xe/0x20 21:44:04 ...: [ 482.520327] [<ffffffff811a6cb0>] read_dev_sector+0x30/0xa0 21:44:04 ...: [ 482.520334] [<ffffffff811a7fcd>] amiga_partition+0x6d/0x460 21:44:04 ...: [ 482.520341] [<ffffffff811a7938>] check_partition+0x138/0x190 21:44:04 ...: [ 482.520348] [<ffffffff811a7a7a>] rescan_partitions+0xea/0x2f0 21:44:04 ...: [ 482.520355] [<ffffffff811744c7>] __blkdev_get+0x267/0x3d0 21:44:04 ...: [ 482.520361] [<ffffffff81174650>] ? blkdev_open+0x0/0xc0 21:44:04 ...: [ 482.520367] [<ffffffff81174640>] blkdev_get+0x10/0x20 21:44:04 ...: [ 482.520373] [<ffffffff811746c1>] blkdev_open+0x71/0xc0 21:44:04 ...: [ 482.520380] [<ffffffff811419f3>] __dentry_open+0x113/0x370 21:44:04 ...: [ 482.520388] [<ffffffff81253f8f>] ? security_inode_permission+0x1f/0x30 21:44:04 ...: [ 482.520396] [<ffffffff8114de3f>] ? inode_permission+0xaf/0xd0 21:44:04 ...: [ 482.520403] [<ffffffff81141d67>] nameidata_to_filp+0x57/0x70 21:44:04 ...: [ 482.520410] [<ffffffff8115207a>] do_filp_open+0x2da/0xba0 21:44:04 ...: [ 482.520417] [<ffffffff811134a8>] ? unmap_vmas+0x178/0x310 21:44:04 ...: [ 482.520426] [<ffffffff8115dbfa>] ? alloc_fd+0x10a/0x150 21:44:04 ...: [ 482.520432] [<ffffffff81141769>] do_sys_open+0x69/0x170 21:44:04 ...: [ 482.520438] [<ffffffff811418b0>] sys_open+0x20/0x30 21:44:04 ...: [ 482.520447] [<ffffffff810121b2>] system_call_fastpath+0x16/0x1b 21:44:04 ...: [ 482.520458] INFO: task mdadm:2283 blocked for more than 120 seconds. 21:44:04 ...: [ 482.520462] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. 21:44:04 ...: [ 482.520467] mdadm D 0000000000000000 0 2283 2212 0x00000000 21:44:04 ...: [ 482.520475] ffff88002cca7d98 0000000000000086 0000000000015bc0 0000000000015bc0 21:44:04 ...: [ 482.520483] ffff88002ededf78 ffff88002cca7fd8 0000000000015bc0 ffff88002ededbc0 21:44:04 ...: [ 482.520490] 0000000000015bc0 ffff88002cca7fd8 0000000000015bc0 ffff88002ededf78 21:44:04 ...: [ 482.520498] Call Trace: 21:44:04 ...: [ 482.520508] [<ffffffff81543a97>] __mutex_lock_slowpath+0xf7/0x180 21:44:04 ...: [ 482.520515] [<ffffffff8154397b>] mutex_lock+0x2b/0x50 21:44:04 ...: [ 482.520521] [<ffffffff8117404d>] __blkdev_put+0x3d/0x190 21:44:04 ...: [ 482.520527] [<ffffffff811741b0>] blkdev_put+0x10/0x20 21:44:04 ...: [ 482.520533] [<ffffffff811741f3>] blkdev_close+0x33/0x60 21:44:04 ...: [ 482.520541] [<ffffffff81145375>] __fput+0xf5/0x210 21:44:04 ...: [ 482.520547] [<ffffffff811454b5>] fput+0x25/0x30 21:44:04 ...: [ 482.520554] [<ffffffff811415ad>] filp_close+0x5d/0x90 21:44:04 ...: [ 482.520560] [<ffffffff81141697>] sys_close+0xb7/0x120 21:44:04 ...: [ 482.520568] [<ffffffff810121b2>] system_call_fastpath+0x16/0x1b 21:44:04 ...: [ 482.520574] INFO: task md0_reshape:2287 blocked for more than 120 seconds. 21:44:04 ...: [ 482.520578] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. 21:44:04 ...: [ 482.520582] md0_reshape D ffff88003aee96f0 0 2287 2 0x00000000 21:44:04 ...: [ 482.520590] ffff88003cf05a70 0000000000000046 0000000000015bc0 0000000000015bc0 21:44:04 ...: [ 482.520597] ffff88003aee9aa8 ffff88003cf05fd8 0000000000015bc0 ffff88003aee96f0 21:44:04 ...: [ 482.520605] 0000000000015bc0 ffff88003cf05fd8 0000000000015bc0 ffff88003aee9aa8 21:44:04 ...: [ 482.520612] Call Trace: 21:44:04 ...: [ 482.520623] [<ffffffffa0224892>] get_active_stripe+0x312/0x3f0 [raid456] 21:44:04 ...: [ 482.520633] [<ffffffff81059ae0>] ? default_wake_function+0x0/0x20 21:44:04 ...: [ 482.520643] [<ffffffffa0226f80>] reshape_request+0x4c0/0x9a0 [raid456] 21:44:04 ...: [ 482.520651] [<ffffffff81084790>] ? autoremove_wake_function+0x0/0x40 21:44:04 ...: [ 482.520661] [<ffffffffa022777a>] sync_request+0x31a/0x3a0 [raid456] 21:44:04 ...: [ 482.520668] [<ffffffff81052713>] ? __wake_up+0x53/0x70 21:44:04 ...: [ 482.520675] [<ffffffff814156b1>] md_do_sync+0x621/0xbb0 21:44:04 ...: [ 482.520685] [<ffffffff810387b9>] ? default_spin_lock_flags+0x9/0x10 21:44:04 ...: [ 482.520692] [<ffffffff8141640c>] md_thread+0x5c/0x130 21:44:04 ...: [ 482.520699] [<ffffffff81084790>] ? autoremove_wake_function+0x0/0x40 21:44:04 ...: [ 482.520705] [<ffffffff814163b0>] ? md_thread+0x0/0x130 21:44:04 ...: [ 482.520711] [<ffffffff81084416>] kthread+0x96/0xa0 21:44:04 ...: [ 482.520718] [<ffffffff810131ea>] child_rip+0xa/0x20 21:44:04 ...: [ 482.520725] [<ffffffff81084380>] ? kthread+0x0/0xa0 21:44:04 ...: [ 482.520730] [<ffffffff810131e0>] ? child_rip+0x0/0x20 21:44:04 ...: [ 482.520735] INFO: task mdadm:2288 blocked for more than 120 seconds. 21:44:04 ...: [ 482.520739] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. 21:44:04 ...: [ 482.520743] mdadm D 0000000000000000 0 2288 1 0x00000000 21:44:04 ...: [ 482.520751] ffff88002cca9c18 0000000000000086 0000000000015bc0 0000000000015bc0 21:44:04 ...: [ 482.520759] ffff88003aee83b8 ffff88002cca9fd8 0000000000015bc0 ffff88003aee8000 21:44:04 ...: [ 482.520767] 0000000000015bc0 ffff88002cca9fd8 0000000000015bc0 ffff88003aee83b8 21:44:04 ...: [ 482.520774] Call Trace: 21:44:04 ...: [ 482.520782] [<ffffffff81543a97>] __mutex_lock_slowpath+0xf7/0x180 21:44:04 ...: [ 482.520790] [<ffffffff812a6d50>] ? exact_match+0x0/0x10 21:44:04 ...: [ 482.520797] [<ffffffff8154397b>] mutex_lock+0x2b/0x50 21:44:04 ...: [ 482.520804] [<ffffffff811742c8>] __blkdev_get+0x68/0x3d0 21:44:04 ...: [ 482.520810] [<ffffffff81174650>] ? blkdev_open+0x0/0xc0 21:44:04 ...: [ 482.520816] [<ffffffff81174640>] blkdev_get+0x10/0x20 21:44:04 ...: [ 482.520822] [<ffffffff811746c1>] blkdev_open+0x71/0xc0 21:44:04 ...: [ 482.520829] [<ffffffff811419f3>] __dentry_open+0x113/0x370 21:44:04 ...: [ 482.520837] [<ffffffff81253f8f>] ? security_inode_permission+0x1f/0x30 21:44:04 ...: [ 482.520843] [<ffffffff8114de3f>] ? inode_permission+0xaf/0xd0 21:44:04 ...: [ 482.520850] [<ffffffff81141d67>] nameidata_to_filp+0x57/0x70 21:44:04 ...: [ 482.520857] [<ffffffff8115207a>] do_filp_open+0x2da/0xba0 21:44:04 ...: [ 482.520864] [<ffffffff810ff0e1>] ? lru_cache_add_lru+0x21/0x40 21:44:04 ...: [ 482.520871] [<ffffffff8111109c>] ? do_anonymous_page+0x11c/0x330 21:44:04 ...: [ 482.520878] [<ffffffff81115d5f>] ? handle_mm_fault+0x31f/0x3c0 21:44:04 ...: [ 482.520885] [<ffffffff8115dbfa>] ? alloc_fd+0x10a/0x150 21:44:04 ...: [ 482.520891] [<ffffffff81141769>] do_sys_open+0x69/0x170 21:44:04 ...: [ 482.520897] [<ffffffff811418b0>] sys_open+0x20/0x30 21:44:04 ...: [ 482.520905] [<ffffffff810121b2>] system_call_fastpath+0x16/0x1b 21:46:04 ...: [ 602.520053] INFO: task mdadm:1937 blocked for more than 120 seconds. 21:46:04 ...: [ 602.520059] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. 21:46:04 ...: [ 602.520065] mdadm D 00000000ffffffff 0 1937 1 0x00000000 21:46:04 ...: [ 602.520075] ffff88002ef4f5d8 0000000000000082 0000000000015bc0 0000000000015bc0 21:46:04 ...: [ 602.520084] ffff88002eb5b198 ffff88002ef4ffd8 0000000000015bc0 ffff88002eb5ade0 21:46:04 ...: [ 602.520091] 0000000000015bc0 ffff88002ef4ffd8 0000000000015bc0 ffff88002eb5b198 21:46:04 ...: [ 602.520099] Call Trace: 21:46:04 ...: [ 602.520127] [<ffffffffa0224892>] get_active_stripe+0x312/0x3f0 [raid456] 21:46:04 ...: [ 602.520142] [<ffffffff81059ae0>] ? default_wake_function+0x0/0x20 21:46:04 ...: [ 602.520153] [<ffffffffa0228413>] make_request+0x243/0x4b0 [raid456] 21:46:04 ...: [ 602.520162] [<ffffffffa0221a90>] ? release_stripe+0x50/0x70 [raid456] 21:46:04 ...: [ 602.520171] [<ffffffff81084790>] ? autoremove_wake_function+0x0/0x40 21:46:04 ...: [ 602.520180] [<ffffffff81414df0>] md_make_request+0xc0/0x130 21:46:04 ...: [ 602.520187] [<ffffffff81414df0>] ? md_make_request+0xc0/0x130 21:46:04 ...: [ 602.520197] [<ffffffff8129f8c1>] generic_make_request+0x1b1/0x4f0 21:46:04 ...: [ 602.520206] [<ffffffff810f6515>] ? mempool_alloc_slab+0x15/0x20 21:46:04 ...: [ 602.520215] [<ffffffff8116c2ec>] ? alloc_buffer_head+0x1c/0x60 21:46:04 ...: [ 602.520222] [<ffffffff8129fc80>] submit_bio+0x80/0x110 21:46:04 ...: [ 602.520229] [<ffffffff8116c849>] submit_bh+0xf9/0x140 21:46:04 ...: [ 602.520237] [<ffffffff8116f124>] block_read_full_page+0x274/0x3b0 21:46:04 ...: [ 602.520244] [<ffffffff81172c90>] ? blkdev_get_block+0x0/0x70 21:46:04 ...: [ 602.520252] [<ffffffff8110d875>] ? __inc_zone_page_state+0x35/0x40 21:46:04 ...: [ 602.520259] [<ffffffff810f46d8>] ? add_to_page_cache_locked+0xe8/0x160 21:46:04 ...: [ 602.520266] [<ffffffff81173d78>] blkdev_readpage+0x18/0x20 21:46:04 ...: [ 602.520273] [<ffffffff810f484b>] __read_cache_page+0x7b/0xe0 21:46:04 ...: [ 602.520279] [<ffffffff81173d60>] ? blkdev_readpage+0x0/0x20 21:46:04 ...: [ 602.520285] [<ffffffff81173d60>] ? blkdev_readpage+0x0/0x20 21:46:04 ...: [ 602.520292] [<ffffffff810f57dc>] do_read_cache_page+0x3c/0x120 21:46:04 ...: [ 602.520300] [<ffffffff810f5909>] read_cache_page_async+0x19/0x20 21:46:04 ...: [ 602.520306] [<ffffffff810f591e>] read_cache_page+0xe/0x20 21:46:04 ...: [ 602.520314] [<ffffffff811a6cb0>] read_dev_sector+0x30/0xa0 21:46:04 ...: [ 602.520321] [<ffffffff811a7fcd>] amiga_partition+0x6d/0x460 21:46:04 ...: [ 602.520328] [<ffffffff811a7938>] check_partition+0x138/0x190 21:46:04 ...: [ 602.520335] [<ffffffff811a7a7a>] rescan_partitions+0xea/0x2f0 21:46:04 ...: [ 602.520342] [<ffffffff811744c7>] __blkdev_get+0x267/0x3d0 21:46:04 ...: [ 602.520348] [<ffffffff81174650>] ? blkdev_open+0x0/0xc0 21:46:04 ...: [ 602.520354] [<ffffffff81174640>] blkdev_get+0x10/0x20 21:46:04 ...: [ 602.520359] [<ffffffff811746c1>] blkdev_open+0x71/0xc0 21:46:04 ...: [ 602.520367] [<ffffffff811419f3>] __dentry_open+0x113/0x370 21:46:04 ...: [ 602.520375] [<ffffffff81253f8f>] ? security_inode_permission+0x1f/0x30 21:46:04 ...: [ 602.520383] [<ffffffff8114de3f>] ? inode_permission+0xaf/0xd0 21:46:04 ...: [ 602.520390] [<ffffffff81141d67>] nameidata_to_filp+0x57/0x70 21:46:04 ...: [ 602.520397] [<ffffffff8115207a>] do_filp_open+0x2da/0xba0 21:46:04 ...: [ 602.520404] [<ffffffff811134a8>] ? unmap_vmas+0x178/0x310 21:46:04 ...: [ 602.520413] [<ffffffff8115dbfa>] ? alloc_fd+0x10a/0x150 21:46:04 ...: [ 602.520419] [<ffffffff81141769>] do_sys_open+0x69/0x170 21:46:04 ...: [ 602.520425] [<ffffffff811418b0>] sys_open+0x20/0x30 21:46:04 ...: [ 602.520434] [<ffffffff810121b2>] system_call_fastpath+0x16/0x1b 21:46:04 ...: [ 602.520443] INFO: task mdadm:2283 blocked for more than 120 seconds. 21:46:04 ...: [ 602.520447] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. 21:46:04 ...: [ 602.520451] mdadm D 0000000000000000 0 2283 2212 0x00000000 21:46:04 ...: [ 602.520460] ffff88002cca7d98 0000000000000086 0000000000015bc0 0000000000015bc0 21:46:04 ...: [ 602.520468] ffff88002ededf78 ffff88002cca7fd8 0000000000015bc0 ffff88002ededbc0 21:46:04 ...: [ 602.520475] 0000000000015bc0 ffff88002cca7fd8 0000000000015bc0 ffff88002ededf78 21:46:04 ...: [ 602.520483] Call Trace: 21:46:04 ...: [ 602.520492] [<ffffffff81543a97>] __mutex_lock_slowpath+0xf7/0x180 21:46:04 ...: [ 602.520500] [<ffffffff8154397b>] mutex_lock+0x2b/0x50 21:46:04 ...: [ 602.520506] [<ffffffff8117404d>] __blkdev_put+0x3d/0x190 21:46:04 ...: [ 602.520512] [<ffffffff811741b0>] blkdev_put+0x10/0x20 21:46:04 ...: [ 602.520518] [<ffffffff811741f3>] blkdev_close+0x33/0x60 21:46:04 ...: [ 602.520526] [<ffffffff81145375>] __fput+0xf5/0x210 21:46:04 ...: [ 602.520533] [<ffffffff811454b5>] fput+0x25/0x30 21:46:04 ...: [ 602.520539] [<ffffffff811415ad>] filp_close+0x5d/0x90 21:46:04 ...: [ 602.520545] [<ffffffff81141697>] sys_close+0xb7/0x120 21:46:04 ...: [ 602.520552] [<ffffffff810121b2>] system_call_fastpath+0x16/0x1b

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• Large number of simultaneous long-running operations in Qt

  - by Hostile Fork

  I have some long-running operations that number in the hundreds. At the moment they are each on their own thread. My main goal in using threads is not to speed these operations up. The more important thing in this case is that they appear to run simultaneously. I'm aware of cooperative multitasking and fibers. However, I'm trying to avoid anything that would require touching the code in the operations, e.g. peppering them with things like yieldToScheduler(). I also don't want to prescribe that these routines be stylized to be coded to emit queues of bite-sized task items...I want to treat them as black boxes. For the moment I can live with these downsides: Maximum # of threads tend to be O(1000) Cost per thread is O(1MB) To address the bad cache performance due to context-switches, I did have the idea of a timer which would juggle the priorities such that only idealThreadCount() threads were ever at Normal priority, with all the rest set to Idle. This would let me widen the timeslices, which would mean fewer context switches and still be okay for my purposes. Question #1: Is that a good idea at all? One certain downside is it won't work on Linux (docs say no QThread::setPriority() there). Question #2: Any other ideas or approaches? Is QtConcurrent thinking about this scenario? (Some related reading: how-many-threads-does-it-take-to-make-them-a-bad-choice, many-threads-or-as-few-threads-as-possible, maximum-number-of-threads-per-process-in-linux)

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• Make Python Socket Server More Efficient

  - by BenMills

  I have very little experience working with sockets and multithreaded programming so to learn more I decided to see if I could hack together a little python socket server to power a chat room. I ended up getting it working pretty well but then I noticed my server's CPU usage spiked up over 100% when I had it running in the background. Here is my code in full: http://gist.github.com/332132 I know this is a pretty open ended question so besides just helping with my code are there any good articles I could read that could help me learn more about this? My full code: import select import socket import sys import threading from daemon import Daemon class Server: def __init__(self): self.host = '' self.port = 9998 self.backlog = 5 self.size = 1024 self.server = None self.threads = [] self.send_count = 0 def open_socket(self): try: self.server = socket.socket(socket.AF_INET6, socket.SOCK_STREAM) self.server.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1) self.server.bind((self.host,self.port)) self.server.listen(5) print "Server Started..." except socket.error, (value,message): if self.server: self.server.close() print "Could not open socket: " + message sys.exit(1) def remove_thread(self, t): t.join() def send_to_children(self, msg): self.send_count = 0 for t in self.threads: t.send_msg(msg) print 'Sent to '+str(self.send_count)+" of "+str(len(self.threads)) def run(self): self.open_socket() input = [self.server,sys.stdin] running = 1 while running: inputready,outputready,exceptready = select.select(input,[],[]) for s in inputready: if s == self.server: # handle the server socket c = Client(self.server.accept(), self) c.start() self.threads.append(c) print "Num of clients: "+str(len(self.threads)) self.server.close() for c in self.threads: c.join() class Client(threading.Thread): def __init__(self,(client,address), server): threading.Thread.__init__(self) self.client = client self.address = address self.size = 1024 self.server = server self.running = True def send_msg(self, msg): if self.running: self.client.send(msg) self.server.send_count += 1 def run(self): while self.running: data = self.client.recv(self.size) if data: print data self.server.send_to_children(data) else: self.running = False self.server.threads.remove(self) self.client.close() """ Run Server """ class DaemonServer(Daemon): def run(self): s = Server() s.run() if __name__ == "__main__": d = DaemonServer('/var/servers/fserver.pid') if len(sys.argv) == 2: if 'start' == sys.argv[1]: d.start() elif 'stop' == sys.argv[1]: d.stop() elif 'restart' == sys.argv[1]: d.restart() else: print "Unknown command" sys.exit(2) sys.exit(0) else: print "usage: %s start|stop|restart" % sys.argv[0] sys.exit(2)

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• Can't get any speedup from parallelizing Quicksort using Pthreads

  - by Murat Ayfer

  I'm using Pthreads to create a new tread for each partition after the list is split into the right and left halves (less than and greater than the pivot). I do this recursively until I reach the maximum number of allowed threads. When I use printfs to follow what goes on in the program, I clearly see that each thread is doing its delegated work in parallel. However using a single process is always the fastest. As soon as I try to use more threads, the time it takes to finish almost doubles, and keeps increasing with number of threads. I am allowed to use up to 16 processors on the server I am running it on. The algorithm goes like this: Split array into right and left by comparing the elements to the pivot. Start a new thread for the right and left, and wait until the threads join back. If there are more available threads, they can create more recursively. Each thread waits for its children to join. Everything makes sense to me, and sorting works perfectly well, but more threads makes it slow down immensely. I tried setting a minimum number of elements per partition for a thread to be started (e.g. 50000). I tried an approach where when a thread is done, it allows another thread to be started, which leads to hundreds of threads starting and finishing throughout. I think the overhead was way too much. So I got rid of that, and if a thread was done executing, no new thread was created. I got a little more speedup but still a lot slower than a single process. The code I used is below. http://pastebin.com/UaGsjcq2 Does anybody have any clue as to what I could be doing wrong?

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• thread reaches end but isn't removed

  - by pstanton

  I create a bunch of threads to do some processing: new Thread("upd-" + id){ @Override public void run(){ try{ doSomething(); } catch (Throwable e){ LOG.error("error", e); } finally{ LOG.debug("thread death"); } } }.start(); I know i should be using a threadPool but i need to understand the following problem before i change it: I'm using eclipse's debugger and looking at the threads in the debug pane which lists active threads. Many of them complete as you would expect, and are removed from the debug pane, however some seem to stay in the list of active threads even though the log shows the "thread death" entry for these. When i attempt to debug these threads, they either do not pause for debugging or show an error dialog: "A timeout occurred while retrieving stack frames for thread: upd-...". there is some synchronization going on within the doSomething() call but i'm fairly sure it's ok and since the "thread death" log is being called i'm assuming these threads aren't deadlocked in that method. i don't do any Thread.join()s, however i do call a third party API but doubt they do either. Can anyone think of another reason these threads are lingering? Thanks. EDIT: I created this test to check the Garbage Collection theory: Thread thread = new Thread("!!!!!!!!!!!!!!!!") { @Override public void run() { System.out.println("running"); ThreadUs.sleepQuiet(5000); System.out.println("finished"); // <-- thread removed from list here } }; thread.start(); ThreadUs.sleepQuiet(10000); System.out.println(thread.isAlive()); // <-- thread already removed from list but hasn't been GC'd ThreadUs.sleepQuiet(10000); this proves that it is nothing to do with garbage collection as eclipse removes the thread from the thread list as soon as it completes and isn't waiting for the object to be de-referenced/GC'd.

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• Thread management advice - Is TPL a good idea?

  - by Ian

  I'm hoping to get some advice on the use of thread managment and hopefully the task parallel library, because I'm not sure I've been going down the correct route. Probably best is that I give an outline of what I'm trying to do. Given a Problem I need to generate a Solution using a heuristic based algorithm. I start of by calculating a base solution, this operation I don't think can be parallelised so we don't need to worry about. Once the inital solution has been generated, I want to trigger n threads, which attempt to find a better solution. These threads need to do a couple of things: They need to be initalized with a different 'optimization metric'. In other words they are attempting to optimize different things, with a precedence level set within code. This means they all run slightly different calculation engines. I'm not sure if I can do this with the TPL.. If one of the threads finds a better solution that the currently best known solution (which needs to be shared across all threads) then it needs to update the best solution, and force a number of other threads to restart (again this depends on precedence levels of the optimization metrics). I may also wish to combine certain calculations across threads (e.g. keep a union of probabilities for a certain approach to the problem). This is probably more optional though. The whole system needs to be thread safe obviously and I want it to be running as fast as possible. I tried quite an implementation that involved managing my own threads and shutting them down etc, but it started getting quite complicated, and I'm now wondering if the TPL might be better. I'm wondering if anyone can offer any general guidance? Thanks...

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• Concurrent Programming:Should I write a sequential program first, then add thread safety?

  - by evthim

  I'm working on a project where we have to create a number of threads(actual number will be inputted in by testers (TA's)). I'm having trouble not only with the programming but also with the design, I can't wrap my head around all of the threads that will be invoked and where I might cause errors. The project is due soon so I don't want to waste time on this if it'll actually set me back, but I was wondering if I should write the program like only one thread will be running and everything should be sequential and then later go back and try to add the thread safety parts of the code? Would that take twice the original amount of time? Project Description: Note:I'm going to be as vague as possible so I don't violate any honor codes, sorry :( your program should accept n number of objectA threads, m number of objectB threads, and r number of objectC objectB threads interact with code in objectA. objectA threads interact with code in objectB and objectC objectB and objectC don't directly interact, but do so indirectly through objectA -ex: objectB needs something from objectA. objectA gets the result for that something by calling objectC my confusion stems mostly from the fact that all of this interactions will be done by m+n threads and there are various restrictions throughout the descriptions, like objectB can request something from objectA, and objectA has to wait for objectC to finish that something before returning it to objectB. Also each objectA thread can only work on one instruction from objectB at a time, etc. etc. I just want to know if I write the code so that there is only 1 objectA, 1 objectB and 1 object C, can I go back and easily modify it so that those 1's can be changed to m, n and r? Sorry again, if my description is a little bit confusing.

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• Get the first and last posts in a thread

  - by Grampa

  I am trying to code a forum website and I want to display a list of threads. Each thread should be accompanied by info about the first post (the "head" of the thread) as well as the last. My current database structure is the following: threads table: id - int, PK, not NULL, auto-increment name - varchar(255) posts table: id - int, PK, not NULL, auto-increment thread_id - FK for threads The tables have other fields as well, but they are not relevant for the query. I am interested in querying threads and somehow JOINing with posts so that I obtain both the first and last post for each thread in a single query (with no subqueries). So far I am able to do it using multiple queries, and I have defined the first post as being: SELECT * FROM threads t LEFT JOIN posts p ON t.id = p.thread_id ORDER BY p.id LIMIT 0, 1 The last post is pretty much the same except for ORDER BY id DESC. Now, I could select multiple threads with their first or last posts, by doing: SELECT * FROM threads t LEFT JOIN posts p ON t.id = p.thread_id ORDER BY p.id GROUP BY t.id But of course I can't get both at once, since I would need to sort both ASC and DESC at the same time. What is the solution here? Is it even possible to use a single query? Is there any way I could change the structure of my tables to facilitate this? If this is not doable, then what tips could you give me to improve the query performance in this particular situation?

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• Can one thread open a socket and other thread close it?

  - by Pkp

  I have some kernel threads in Linux kernel, inside my KLM. I have a server thread, that listens to the channel, Once it sees there is an incoming connection, it creates an accept socket, accepts the connection and spawns a child thread. It also passes the accepted socket to the child kernel thread as the (void *) argument. The code is working fine. I had a design question. Suppose now the threads have to be terminated, main and the child threads, what would be the best way to close the accept socket. I can see two ways, 1] The main thread waits for all the child threads to exit, each of the child threads close the accept sockets while exiting, the last child thread passes a signal to the main thread for it to exit . Here even though the main thread was the one that created the accept socket, the child threads close that socket, and they do this before the main thread exits. So is this acceptable? Any problems you guys forsee here? 2] Second is the main thread closes all the accept sockets it created before it exits. But there may be a possibility(corner case) that the main thread gets an exception and will have to close, so if it closes the accept sockets before exiting, the child threads using that socket will be in danger. Hence i am using the first case i mentioned.Let me know what you guys think?

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• Apt-get update through tor

  - by Alexander

  I'm trying to update my apt-get list. In my country a lot of sites are blocked or have been blocked from companies. When I use a proxy for the whole system I get errors, tor works perfectly when browsing. My question is can I update apt-get through a connection from tor? I mean I want to unblock the blocked sites using tor connection so I can perform "apt-get update" without errors ... Thanks in advance. Edit BTW : I'm using Ubuntu 13.10 and Tor 0.2.21 alexander@Alexander-PC:~$ sudo apt-get update [sudo] password for alexander: Ign http://extras.ubuntu.com saucy InRelease Ign http://security.ubuntu.com saucy-security InRelease Ign http://us.archive.ubuntu.com saucy InRelease Hit http://extras.ubuntu.com saucy Release.gpg Get:1 http://dl.google.com stable InRelease [1,540 B] 100% [1 InRelease gpgv 1,540 B] [Waiting for headers] [Waiting for headers] [WaSplitting up/var/lib/apt/lists/partial/dl.google.com_linux_chrome_deb_dists_stabIgn http://dl.google.com stable InRelease E: GPG error: http://dl.google.com stable InRelease: Clearsigned file isn't valid, got 'NODATA' (does the network require authentication?

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• How do I get wireless to work on a Dell Mini 1018 with Realtek RTL 8188CE Network Adapter?

  - by Laurence Nagel

  My Dell Mini 1018 used to work fine with Ubuntu 12.04 with no problems connecting with the wireless card. Then I made the big mistake of attempting to disable WiFi by right-clicking on the wireless applet and un-checking "Enable Wireless." Since then, I cannot get wireless working again. The wireless applet reports that "wireless is disabled by hardware switch" but there is no hardware switch on this computer. Issuing a rfkill list yields the following: 0: dell-wifi: Wireless LAN Soft blocked: yes Hard block: yes 1: phy0: Wireless LAN Soft blocked: no Hard blocked: yes I'm in way over my head, and my computer is now useless. Help!!!

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• Atheros 922 PCI WIFI is disabled in Unity but enabled in terminal - How to get it to work?

  - by zewone

  I am trying to get my PCI Wireless Atheros 922 card to work. It is disabled in Unity: both the network utility and the desktop (see screenshot http://www.amisdurailhalanzy.be/Screenshot%20from%202012-10-25%2013:19:54.png) I tried many different advises on many different forums. Installed 12.10 instead of 12.04, enabled all interfaces... etc. I have read about the aht9 driver... The terminal shows no hw or sw lock for the Atheros card, nevertheless, it is still disabled. Nothing worked so far, the card is still disabled. Any help is much appreciated. Here are more tech details: myuser@adri1:~$ sudo lshw -C network *-network:0 DISABLED description: Wireless interface product: AR922X Wireless Network Adapter vendor: Atheros Communications Inc. physical id: 2 bus info: pci@0000:03:02.0 logical name: wlan1 version: 01 serial: 00:18:e7:cd:68:b1 width: 32 bits clock: 66MHz capabilities: pm bus_master cap_list ethernet physical wireless configuration: broadcast=yes driver=ath9k driverversion=3.5.0-17-generic firmware=N/A latency=168 link=no multicast=yes wireless=IEEE 802.11bgn resources: irq:18 memory:d8000000-d800ffff *-network:1 description: Ethernet interface product: VT6105/VT6106S [Rhine-III] vendor: VIA Technologies, Inc. physical id: 6 bus info: pci@0000:03:06.0 logical name: eth0 version: 8b serial: 00:11:09:a3:76:4a size: 10Mbit/s capacity: 100Mbit/s width: 32 bits clock: 33MHz capabilities: pm bus_master cap_list ethernet physical tp mii 10bt 10bt-fd 100bt 100bt-fd autonegotiation configuration: autonegotiation=on broadcast=yes driver=via-rhine driverversion=1.5.0 duplex=half latency=32 link=no maxlatency=8 mingnt=3 multicast=yes port=MII speed=10Mbit/s resources: irq:18 ioport:d300(size=256) memory:d8013000-d80130ff *-network DISABLED description: Wireless interface physical id: 1 bus info: usb@1:8.1 logical name: wlan0 serial: 00:11:09:51:75:36 capabilities: ethernet physical wireless configuration: broadcast=yes driver=rt2500usb driverversion=3.5.0-17-generic firmware=N/A link=no multicast=yes wireless=IEEE 802.11bg myuser@adri1:~$ sudo rfkill list all 0: hci0: Bluetooth Soft blocked: no Hard blocked: no 1: phy1: Wireless LAN Soft blocked: no Hard blocked: yes 2: phy0: Wireless LAN Soft blocked: no Hard blocked: no myuser@adri1:~$ dmesg | grep wlan0 [ 15.114235] IPv6: ADDRCONF(NETDEV_UP): wlan0: link is not ready myuser@adri1:~$ dmesg | egrep 'ath|firm' [ 14.617562] ath: EEPROM regdomain: 0x30 [ 14.617568] ath: EEPROM indicates we should expect a direct regpair map [ 14.617572] ath: Country alpha2 being used: AM [ 14.617575] ath: Regpair used: 0x30 [ 14.637778] ieee80211 phy0: >Selected rate control algorithm 'ath9k_rate_control' [ 14.639410] Registered led device: ath9k-phy0 myuser@adri1:~$ dmesg | grep wlan1 [ 15.119922] IPv6: ADDRCONF(NETDEV_UP): wlan1: link is not ready myuser@adri1:~$ lspci -nn | grep 'Atheros' 03:02.0 Network controller [0280]: Atheros Communications Inc. AR922X Wireless Network Adapter [168c:0029] (rev 01) myuser@adri1:~$ sudo ifconfig eth0 Link encap:Ethernet HWaddr 00:11:09:a3:76:4a inet addr:192.168.2.2 Bcast:192.168.2.255 Mask:255.255.255.0 inet6 addr: fe80::211:9ff:fea3:764a/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:5457 errors:0 dropped:0 overruns:0 frame:0 TX packets:2548 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:3425684 (3.4 MB) TX bytes:282192 (282.1 KB) lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:16436 Metric:1 RX packets:590 errors:0 dropped:0 overruns:0 frame:0 TX packets:590 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:53729 (53.7 KB) TX bytes:53729 (53.7 KB) myuser@adri1:~$ sudo iwconfig wlan0 IEEE 802.11bg ESSID:off/any Mode:Managed Access Point: Not-Associated Tx-Power=off Retry long limit:7 RTS thr:off Fragment thr:off Encryption key:off Power Management:on lo no wireless extensions. eth0 no wireless extensions. wlan1 IEEE 802.11bgn ESSID:off/any Mode:Managed Access Point: Not-Associated Tx-Power=0 dBm Retry long limit:7 RTS thr:off Fragment thr:off Encryption key:off Power Management:off myuser@adri1:~$ lsmod | grep "ath9k" ath9k 116549 0 mac80211 461161 3 rt2x00usb,rt2x00lib,ath9k ath9k_common 13783 1 ath9k ath9k_hw 376155 2 ath9k,ath9k_common ath 19187 3 ath9k,ath9k_common,ath9k_hw cfg80211 175375 4 rt2x00lib,ath9k,mac80211,ath myuser@adri1:~$ iwlist scan wlan0 Failed to read scan data : Network is down lo Interface doesn't support scanning. eth0 Interface doesn't support scanning. wlan1 Failed to read scan data : Network is down myuser@adri1:~$ lsb_release -d Description: Ubuntu 12.10 myuser@adri1:~$ uname -mr 3.5.0-17-generic i686  Any help much appreciated... Thanks, Philippe 31-10-2012 ... I have some more updates. When I do the following command it does see my Wifi router... So even if it is still disabled... the card seems to work and see the router (ESSID:"5791BC26-CE9C-11D1-97BF-0000F81E") See below: sudo iwlist wlan1 scanning wlan1 Scan completed : Cell 01 - Address: 00:19:70:8F:B0:EA Channel:10 Frequency:2.457 GHz (Channel 10) Quality=51/70 Signal level=-59 dBm Encryption key:on ESSID:"5791BC26-CE9C-11D1-97BF-0000F81E" Bit Rates:1 Mb/s; 2 Mb/s; 5.5 Mb/s; 11 Mb/s; 6 Mb/s 9 Mb/s; 12 Mb/s; 18 Mb/s Bit Rates:24 Mb/s; 36 Mb/s; 48 Mb/s; 54 Mb/s Mode:Master Extra:tsf=000000025dbf2188 Extra: Last beacon: 108ms ago IE: Unknown: 002035373931424332362D434539432D313144312D393742462D3030303046383145 IE: Unknown: 010882848B960C121824 IE: Unknown: 03010A IE: Unknown: 0706424520010D14 IE: IEEE 802.11i/WPA2 Version 1 Group Cipher : TKIP Pairwise Ciphers (2) : CCMP TKIP Authentication Suites (1) : PSK IE: Unknown: 2A0100 IE: Unknown: 32043048606C IE: Unknown: DD180050F2020101030003A4000027A4000042435E0062322F00 IE: Unknown: DD0900037F01010000FF7F IE: Unknown: DD0A00037F04010000000000

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• Intel Centrino Wireless-N 1000 Again ! Ubuntu 13.04 x64

  - by vafa

  First I have to say that I tried everything written about this concept. The problem is that it stops working randomly in 3 main forms : 1 - sometimes it disconnect from wireless network and reconnect automatically 2 - sometimes it disconnect and wont connect no matter what (needs reboot) 3 - some times it's still connected but cannot ping or surf or whatever. I already tried disabling N mod using these commands : sudo modprobe -r iwlwifi modprobe iwlwifi 11n_disable=1 (or 0, whatever) it didn't help . these are the results of lspci, sudo lshw -C network, ifconfig, iwconfig, rfkill list when it disconnected and didn't connect till reboot : ifconfig : eth0 Link encap:Ethernet HWaddr c8:0a:a9:34:65:77 UP BROADCAST MULTICAST MTU:1500 Metric:1 RX packets:1563213476557380 errors:9379306629148050 dropped:3126435543049350 overruns:1563217771524675 frame:7816088857623375 TX packets:1563217771524675 errors:6252871086098700 dropped:0 overruns:1563217771524675 carrier:3126435543049350 collisions:7816088857623375 txqueuelen:1000 RX bytes:1563217771524675 (1.5 PB) TX bytes:1563217771524675 (1.5 PB) ham0 Link encap:Ethernet HWaddr 7a:79:19:a5:e4:93 inet addr:25.165.228.147 Bcast:25.255.255.255 Mask:255.0.0.0 inet6 addr: fe80::7879:19ff:fea5:e493/64 Scope:Link inet6 addr: 2620:9b::19a5:e493/96 Scope:Global UP BROADCAST RUNNING MULTICAST MTU:1404 Metric:1 RX packets:7743 errors:0 dropped:0 overruns:0 frame:0 TX packets:1250 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:500 RX bytes:665642 (665.6 KB) TX bytes:204056 (204.0 KB) lo Link encap:Local Loopback inet addr:127.0.0.1 Mask:255.0.0.0 inet6 addr: ::1/128 Scope:Host UP LOOPBACK RUNNING MTU:65536 Metric:1 RX packets:41138 errors:0 dropped:0 overruns:0 frame:0 TX packets:41138 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:6420962 (6.4 MB) TX bytes:6420962 (6.4 MB) wlan0 Link encap:Ethernet HWaddr 00:1e:64:45:fb:70 inet6 addr: fe80::21e:64ff:fe45:fb70/64 Scope:Link UP BROADCAST MULTICAST MTU:1500 Metric:1 RX packets:286999 errors:0 dropped:0 overruns:0 frame:0 TX packets:226966 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:1000 RX bytes:324386887 (324.3 MB) TX bytes:30674804 (30.6 MB) iwconfig : ham0 no wireless extensions. eth0 no wireless extensions. lo no wireless extensions. wlan0 IEEE 802.11bg ESSID:off/any Mode:Managed Access Point: Not-Associated Tx-Power=14 dBm Retry long limit:7 RTS thr:off Fragment thr:off Power Management:off sudo lshw -C network: *-network description: Wireless interface product: Centrino Wireless-N 1000 [Condor Peak] vendor: Intel Corporation physical id: 0 bus info: pci@0000:07:00.0 logical name: wlan0 version: 00 serial: 00:1e:64:45:fb:70 width: 64 bits clock: 33MHz capabilities: pm msi pciexpress bus_master cap_list ethernet physical wireless configuration: broadcast=yes driver=iwlwifi driverversion=3.8.0-30-generic firmware=39.31.5.1 build 35138 latency=0 link=no multicast=yes wireless=IEEE 802.11bg resources: irq:46 memory:c0400000-c0401fff *-network description: Ethernet interface product: AR8131 Gigabit Ethernet vendor: Qualcomm Atheros physical id: 0 bus info: pci@0000:09:00.0 logical name: eth0 version: c0 serial: c8:0a:a9:34:65:77 capacity: 1Gbit/s width: 64 bits clock: 33MHz capabilities: pm msi pciexpress vpd cap_list ethernet physical tp 10bt 10bt-fd 100bt 100bt-fd 1000bt-fd autonegotiation configuration: autonegotiation=on broadcast=yes driver=atl1c driverversion=1.0.1.1-NAPI latency=0 link=no multicast=yes port=twisted pair resources: irq:47 memory:c0900000-c093ffff ioport:5000(size=128) *-network description: Ethernet interface physical id: 2 logical name: ham0 serial: 7a:79:19:a5:e4:93 size: 10Mbit/s capabilities: ethernet physical configuration: autonegotiation=off broadcast=yes driver=tun driverversion=1.6 duplex=full ip=25.165.228.147 link=yes multicast=yes port=twisted pair speed=10Mbit/s lspci: 00:00.0 Host bridge: Intel Corporation Mobile 4 Series Chipset Memory Controller Hub (rev 07) 00:01.0 PCI bridge: Intel Corporation Mobile 4 Series Chipset PCI Express Graphics Port (rev 07) 00:1a.0 USB controller: Intel Corporation 82801I (ICH9 Family) USB UHCI Controller #4 (rev 03) 00:1a.1 USB controller: Intel Corporation 82801I (ICH9 Family) USB UHCI Controller #5 (rev 03) 00:1a.7 USB controller: Intel Corporation 82801I (ICH9 Family) USB2 EHCI Controller #2 (rev 03) 00:1b.0 Audio device: Intel Corporation 82801I (ICH9 Family) HD Audio Controller (rev 03) 00:1c.0 PCI bridge: Intel Corporation 82801I (ICH9 Family) PCI Express Port 1 (rev 03) 00:1c.3 PCI bridge: Intel Corporation 82801I (ICH9 Family) PCI Express Port 4 (rev 03) 00:1c.5 PCI bridge: Intel Corporation 82801I (ICH9 Family) PCI Express Port 6 (rev 03) 00:1d.0 USB controller: Intel Corporation 82801I (ICH9 Family) USB UHCI Controller #1 (rev 03) 00:1d.1 USB controller: Intel Corporation 82801I (ICH9 Family) USB UHCI Controller #2 (rev 03) 00:1d.2 USB controller: Intel Corporation 82801I (ICH9 Family) USB UHCI Controller #3 (rev 03) 00:1d.3 USB controller: Intel Corporation 82801I (ICH9 Family) USB UHCI Controller #6 (rev 03) 00:1d.7 USB controller: Intel Corporation 82801I (ICH9 Family) USB2 EHCI Controller #1 (rev 03) 00:1e.0 PCI bridge: Intel Corporation 82801 Mobile PCI Bridge (rev 93) 00:1f.0 ISA bridge: Intel Corporation ICH9M LPC Interface Controller (rev 03) 00:1f.2 SATA controller: Intel Corporation 82801IBM/IEM (ICH9M/ICH9M-E) 4 port SATA Controller [AHCI mode] (rev 03) 00:1f.3 SMBus: Intel Corporation 82801I (ICH9 Family) SMBus Controller (rev 03) 01:00.0 VGA compatible controller: NVIDIA Corporation G98M [GeForce G 105M] (rev a1) 07:00.0 Network controller: Intel Corporation Centrino Wireless-N 1000 [Condor Peak] 09:00.0 Ethernet controller: Qualcomm Atheros AR8131 Gigabit Ethernet (rev c0) rfkill list : 1: acer-wireless: Wireless LAN Soft blocked: no Hard blocked: no 2: acer-bluetooth: Bluetooth Soft blocked: yes Hard blocked: no 9: phy0: Wireless LAN Soft blocked: no Hard blocked: no any help will be REALLLYYYY appreciated

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• Does the Instant Preview in Google webmaster tools takes Robot.txt in account?

  - by rockyraw

  Is that the way to go If I want to visually see what the googlebot see? I'm trying to check a folder which I have just blocked in my robots.txt. If I fetch the folder as google bot, It fetches ok, so that doesn't tell me nothing about whether the block is working I know there's a tool to check for blocking, but it is dependent on the input of the robots.txt Therefore I've tried the Instant preview, and I don't get a preview for what the bot sees ("pre-render), so I think that means that it's because the robots.txt blocks it; however - I don't see the bot tried beforehand to access my updated robots.txt, so I'm not sure how does it know that this folder is blocked? (it does preview another new folder, that is not blocked)

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• Thread scheduling Round Robin / scheduling dispatch

  - by MRP

  #include <pthread.h> #include <stdio.h> #include <stdlib.h> #include <semaphore.h> #define NUM_THREADS 4 #define COUNT_LIMIT 13 int done = 0; int count = 0; int quantum = 2; int thread_ids[4] = {0,1,2,3}; int thread_runtime[4] = {0,5,4,7}; pthread_mutex_t count_mutex; pthread_cond_t count_threshold_cv; void * inc_count(void * arg); static sem_t count_sem; int quit = 0; ///////// Inc_Count//////////////// void *inc_count(void *t) { long my_id = (long)t; int i; sem_wait(&count_sem); /////////////CRIT SECTION////////////////////////////////// printf("run_thread = %d\n",my_id); printf("%d \n",thread_runtime[my_id]); for( i=0; i < thread_runtime[my_id];i++) { printf("runtime= %d\n",thread_runtime[my_id]); pthread_mutex_lock(&count_mutex); count++; if (count == COUNT_LIMIT) { pthread_cond_signal(&count_threshold_cv); printf("inc_count(): thread %ld, count = %d Threshold reached.\n", my_id, count); } printf("inc_count(): thread %ld, count = %d, unlocking mutex\n",my_id, count); pthread_mutex_unlock(&count_mutex); sleep(1) ; }//End For sem_post(&count_sem); // Next Thread Enters Crit Section pthread_exit(NULL); } /////////// Count_Watch //////////////// void *watch_count(void *t) { long my_id = (long)t; printf("Starting watch_count(): thread %ld\n", my_id); pthread_mutex_lock(&count_mutex); if (count<COUNT_LIMIT) { pthread_cond_wait(&count_threshold_cv, &count_mutex); printf("watch_count(): thread %ld Condition signal received.\n", my_id); printf("watch_count(): thread %ld count now = %d.\n", my_id, count); } pthread_mutex_unlock(&count_mutex); pthread_exit(NULL); } ////////////////// Main //////////////// int main (int argc, char *argv[]) { int i; long t1=0, t2=1, t3=2, t4=3; pthread_t threads[4]; pthread_attr_t attr; sem_init(&count_sem, 0, 1); /* Initialize mutex and condition variable objects */ pthread_mutex_init(&count_mutex, NULL); pthread_cond_init (&count_threshold_cv, NULL); /* For portability, explicitly create threads in a joinable state */ pthread_attr_init(&attr); pthread_attr_setdetachstate(&attr, PTHREAD_CREATE_JOINABLE); pthread_create(&threads[0], &attr, watch_count, (void *)t1); pthread_create(&threads[1], &attr, inc_count, (void *)t2); pthread_create(&threads[2], &attr, inc_count, (void *)t3); pthread_create(&threads[3], &attr, inc_count, (void *)t4); /* Wait for all threads to complete */ for (i=0; i<NUM_THREADS; i++) { pthread_join(threads[i], NULL); } printf ("Main(): Waited on %d threads. Done.\n", NUM_THREADS); /* Clean up and exit */ pthread_attr_destroy(&attr); pthread_mutex_destroy(&count_mutex); pthread_cond_destroy(&count_threshold_cv); pthread_exit(NULL); } I am trying to learn thread scheduling, there is a lot of technical coding that I don't know. I do know in theory how it should work, but having trouble getting started in code... I know, at least I think, this program is not real time and its not meant to be. Some how I need to create a scheduler dispatch to control the threads in the order they should run... RR FCFS SJF ect. Right now I don't have a dispatcher. What I do have is semaphores/ mutex to control the threads. This code does run FCFS... and I have been trying to use semaphores to create a RR.. but having a lot of trouble. I believe it would be easier to create a dispatcher but I dont know how. I need help, I am not looking for answers just direction.. some sample code will help to understand a bit more. Thank you.

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• gdb : multithreading

  - by Arpit

  Hi Wish to know that I have a program which uses two threads I have put the break point in both the threads. While running the program under gdb I want to switch between the threads and make them run. (thread t1 is active and running and thread t2 hold on the breakpoint I want to stop T1 running and run the T2) Is there any way that I can schedule the threads in gdb. Thanks Arpit

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• Fast inter-process (inter-threaded) communications IPC on large multi-cpu system.

  - by IPC

  What would be the fastest portable bi-directional communication mechanism for inter-process communication where threads from one application need to communicate to multiple threads in another application on the same computer, and the communicating threads can be on different physical CPUs). I assume that it would involve a shared memory and a circular buffer and shared synchronization mechanisms. But shared mutexes are very expensive (and there are limited number of them too) to synchronize when threads are running on different physical CPUs.

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• time required to finish the multithreaded program??

  - by user275131

  A java process starts 5 threads , each thread takes 5 minutes. what will be the minimum and maximum time taken by process? will be of great help if one can explain in java threads and OS threads. Edit : I want to know how java schedule threads at OS level.

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• centos dedicated Server unresponsive for the first time

  - by Ambrose Bwangatto

  server was unresponsive for an hour so i rebooted it and checked /var/log/messages and found this. can anybody point out whats wrong ? Sep 28 07:39:35 www kernel: INFO: task mysqld:22749 blocked for more than 120 seconds. Sep 28 07:39:35 www kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. Sep 28 07:39:35 www kernel: mysqld D ffff810001015120 0 22749 3266 22792 22659 (NOTLB) Sep 28 07:39:35 www kernel: ffff810139d21e58 0000000000000086 ffff810036217000 ffffffff8000f758 Sep 28 07:39:35 www kernel: ffff81020dfd1408 0000000000000007 ffff8101cfbaf7e0 ffff81020fca5080 Sep 28 07:39:35 www kernel: 00017a451524782a 00000000000043b2 ffff8101cfbaf9c8 0000000280009a22 Sep 28 07:39:35 www kernel: Call Trace: Sep 28 07:39:35 www kernel: [<ffffffff8000f758>] generic_permission+0x52/0xca Sep 28 07:39:35 www kernel: [<ffffffff80063c63>] __mutex_lock_slowpath+0x60/0x9b Sep 28 07:39:35 www kernel: [<ffffffff8000cea2>] do_path_lookup+0x294/0x310 Sep 28 07:39:35 www kernel: [<ffffffff80063cad>] .text.lock.mutex+0xf/0x14 Sep 28 07:39:35 www kernel: [<ffffffff8003c618>] do_unlinkat+0x66/0x141 Sep 28 07:39:35 www kernel: [<ffffffff8005d229>] tracesys+0x71/0xe0 Sep 28 07:39:57 www kernel: [<ffffffff8005d28d>] tracesys+0xd5/0xe0 Sep 28 07:39:58 www kernel: Sep 28 07:39:59 www kernel: INFO: task httpd:22679 blocked for more than 120 seconds. Sep 28 07:40:04 www kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. Sep 28 07:40:08 www kernel: httpd D ffff81000100caa0 0 22679 22413 22680 22678 (NOTLB) Sep 28 07:40:51 www kernel: ffff81018b0dbc78 0000000000000086 ffff81018b0dbc88 0000004480063002 Sep 28 07:41:52 www kernel: ffff81000001cc00 0000000000000007 ffff81013ac5e860 ffff81020fc96100 Sep 28 07:43:10 www kernel: 00017a44de6376c8 000000000000a89f ffff81013ac5ea48 000000010001cc00 Sep 28 07:43:38 www kernel: Call Trace: Sep 28 07:44:06 www kernel: [<ffffffff80063c63>] __mutex_lock_slowpath+0x60/0x9b Sep 28 07:44:09 www kernel: [<ffffffff80063cad>] .text.lock.mutex+0xf/0x14 Sep 28 07:44:10 www kernel: [<ffffffff8000d0b2>] do_lookup+0x90/0x1e6 Sep 28 07:44:13 www kernel: [<ffffffff8000a2e9>] __link_path_walk+0xa3a/0xfd1 Sep 28 07:44:16 www kernel: [<ffffffff8000eb8e>] link_path_walk+0x45/0xb8 Sep 28 07:44:16 www kernel: [<ffffffff8000cea2>] do_path_lookup+0x294/0x310 Sep 28 07:44:29 www kernel: [<ffffffff800129ad>] getname+0x15b/0x1c2 Sep 28 07:44:38 www kernel: [<ffffffff80023b60>] __user_walk_fd+0x37/0x4c Sep 28 07:44:42 www kernel: [<ffffffff80028ada>] vfs_stat_fd+0x1b/0x4a Sep 28 07:44:43 www kernel: [<ffffffff8003c69a>] do_unlinkat+0xe8/0x141 Sep 28 07:45:02 www kernel: [<ffffffff80023890>] sys_newstat+0x19/0x31 Sep 28 07:46:18 www kernel: [<ffffffff8005d229>] tracesys+0x71/0xe0 Sep 28 07:46:43 www kernel: [<ffffffff8005d28d>] tracesys+0xd5/0xe0 Sep 28 07:46:55 www kernel: Sep 28 07:46:58 www kernel: INFO: task php:28906 blocked for more than 120 seconds. Sep 28 07:46:59 www kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. Sep 28 07:47:00 www kernel: php D ffff810165127000 0 28906 28905 (NOTLB) Sep 28 07:47:37 www kernel: ffff810078431e58 0000000000000082 ffff810165127000 ffffffff8000f758 Sep 28 07:48:29 www kernel: ffff81020dfd1408 0000000000000007 ffff8101247b9860 ffff810207d0e100 Sep 28 07:48:36 www kernel: 00017a4218932fae 0000000000377111 ffff8101247b9a48 0000000280009a22 Sep 28 07:48:37 www kernel: Call Trace: Sep 28 07:48:37 www kernel: [<ffffffff8000f758>] generic_permission+0x52/0xca Sep 28 07:48:37 www kernel: [<ffffffff80063c63>] __mutex_lock_slowpath+0x60/0x9b Sep 28 07:48:37 www kernel: [<ffffffff8000cea2>] do_path_lookup+0x294/0x310 Sep 28 07:48:41 www kernel: [<ffffffff80063cad>] .text.lock.mutex+0xf/0x14 Sep 28 07:48:41 www kernel: [<ffffffff8003c618>] do_unlinkat+0x66/0x141 Sep 28 07:48:42 www kernel: [<ffffffff8005d229>] tracesys+0x71/0xe0 Sep 28 07:48:42 www kernel: [<ffffffff8005d28d>] tracesys+0xd5/0xe0 Sep 28 07:48:42 www kernel: Sep 28 07:48:43 www kernel: INFO: task php:29032 blocked for more than 120 seconds. Sep 28 07:48:45 www kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. Sep 28 07:48:46 www kernel: php D 0000000000000004 0 29032 1 29050 29024 (NOTLB) Sep 28 07:48:46 www kernel: ffff81006b465dc8 0000000000000086 ffff81020dfd1408 ffffffff80009a22 Sep 28 07:48:46 www kernel: 0000000000000000 0000000000000007 ffff81002946e860 ffff81003c943100 Sep 28 07:48:46 www kernel: 00017a4211450766 000000000024be3d ffff81002946ea48 000000020e42b300 Sep 28 07:48:52 www kernel: Call Trace: Sep 28 07:48:54 www kernel: [<ffffffff80009a22>] __link_path_walk+0x173/0xfd1 Sep 28 07:48:54 www kernel: [<ffffffff8002cc58>] mntput_no_expire+0x19/0x89 Sep 28 07:48:55 www kernel: [<ffffffff8000ebf5>] link_path_walk+0xac/0xb8 Sep 28 07:48:55 www kernel: [<ffffffff80063c63>] __mutex_lock_slowpath+0x60/0x9b Sep 28 07:48:55 www kernel: [<ffffffff80023974>] __path_lookup_intent_open+0x56/0x97 Sep 28 07:48:55 www kernel: [<ffffffff80063cad>] .text.lock.mutex+0xf/0x14 Sep 28 07:48:55 www kernel: [<ffffffff8001b260>] open_namei+0xea/0x718 Sep 28 07:48:59 www kernel: [<ffffffff80067235>] do_page_fault+0x4cc/0x842 Sep 28 07:49:01 www kernel: [<ffffffff80027726>] do_filp_open+0x1c/0x38 Sep 28 07:49:01 www kernel: [<ffffffff8001a09c>] do_sys_open+0x44/0xbe Sep 28 07:49:02 www kernel: [<ffffffff8005d28d>] tracesys+0xd5/0xe0 Sep 28 07:49:03 www kernel: Sep 28 07:49:07 www kernel: INFO: task mysqld:22749 blocked for more than 120 seconds. Sep 28 07:49:09 www kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. Sep 28 07:49:09 www kernel: mysqld D ffff810001015120 0 22749 3266 22792 22659 (NOTLB) Sep 28 07:49:14 www kernel: ffff810139d21e58 0000000000000086 ffff810036217000 ffffffff8000f758 Sep 28 07:49:14 www kernel: ffff81020dfd1408 0000000000000007 ffff8101cfbaf7e0 ffff81020fca5080 Sep 28 07:49:15 www kernel: 00017a451524782a 00000000000043b2 ffff8101cfbaf9c8 0000000280009a22 Sep 28 07:49:15 www kernel: Call Trace: Sep 28 07:49:22 www kernel: [<ffffffff8000f758>] generic_permission+0x52/0xca Sep 28 07:49:23 www kernel: [<ffffffff80063c63>] __mutex_lock_slowpath+0x60/0x9b Sep 28 07:49:23 www kernel: [<ffffffff8000cea2>] do_path_lookup+0x294/0x310 Sep 28 07:49:23 www kernel: [<ffffffff80063cad>] .text.lock.mutex+0xf/0x14 Sep 28 07:49:23 www kernel: [<ffffffff8003c618>] do_unlinkat+0x66/0x141 Sep 28 07:49:23 www kernel: [<ffffffff8005d229>] tracesys+0x71/0xe0 Sep 28 07:49:23 www kernel: [<ffffffff8005d28d>] tracesys+0xd5/0xe0 Sep 28 07:49:23 www kernel: Sep 28 07:49:23 www kernel: INFO: task php:29024 blocked for more than 120 seconds. Sep 28 07:49:23 www kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. Sep 28 07:49:24 www kernel: php D ffff8101920a0000 0 29024 1 29032 29001 (NOTLB) Sep 28 07:49:26 www kernel: ffff8101cca8fe58 0000000000000086 ffff8101920a0000 ffffffff8000f758 Sep 28 07:49:26 www kernel: ffff81020dfd1408 0000000000000007 ffff81000b64b040 ffff8101e05337e0 Sep 28 07:49:26 www kernel: 00017a552aef9f35 0000000000009513 ffff81000b64b228 0000000180009a22 Sep 28 07:49:27 www kernel: Call Trace: Sep 28 07:49:27 www kernel: [<ffffffff8000f758>] generic_permission+0x52/0xca Sep 28 07:49:27 www kernel: [<ffffffff80063c63>] __mutex_lock_slowpath+0x60/0x9b Sep 28 07:49:27 www kernel: [<ffffffff8000cea2>] do_path_lookup+0x294/0x310 Sep 28 07:49:27 www kernel: [<ffffffff80063cad>] .text.lock.mutex+0xf/0x14 Sep 28 07:49:27 www kernel: [<ffffffff8003c618>] do_unlinkat+0x66/0x141 Sep 28 07:49:27 www kernel: [<ffffffff8005d229>] tracesys+0x71/0xe0 Sep 28 07:49:27 www kernel: [<ffffffff8005d28d>] tracesys+0xd5/0xe0 Sep 28 07:49:27 www kernel: Sep 28 07:49:27 www kernel: INFO: task php:29050 blocked for more than 120 seconds. Sep 28 07:49:28 www kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. Sep 28 07:49:28 www kernel: php D ffff810201d95000 0 29050 1 29032 (NOTLB) Sep 28 07:49:28 www kernel: ffff810051e45e58 0000000000000086 ffff810201d95000 ffffffff8000f758 Sep 28 07:49:28 www kernel: ffff81020dfd1408 0000000000000007 ffff81001c23f080 ffff81020f5e2080 Sep 28 07:49:29 www kernel: 00017a5d0bc2aa75 0000000000d0ecfe ffff81001c23f268 0000000280009a22 Sep 28 07:49:29 www kernel: Call Trace: Sep 28 07:49:29 www kernel: [<ffffffff8000f758>] generic_permission+0x52/0xca Sep 28 07:49:29 www kernel: [<ffffffff80063c63>] __mutex_lock_slowpath+0x60/0x9b Sep 28 07:49:29 www kernel: [<ffffffff8000cea2>] do_path_lookup+0x294/0x310 Sep 28 07:49:34 www kernel: [<ffffffff80063cad>] .text.lock.mutex+0xf/0x14 Sep 28 07:49:35 www kernel: [<ffffffff8003c618>] do_unlinkat+0x66/0x141 Sep 28 07:49:37 www kernel: [<ffffffff8005d229>] tracesys+0x71/0xe0 Sep 28 07:49:37 www kernel: [<ffffffff8005d28d>] tracesys+0xd5/0xe0 Sep 28 07:49:37 www kernel: Sep 28 07:49:37 www kernel: INFO: task php:29064 blocked for more than 120 seconds. Sep 28 07:49:37 www kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. Sep 28 07:49:37 www kernel: php D ffff81009c231000 0 29064 29057 (NOTLB) Sep 28 07:49:38 www kernel: ffff8100a5dc7e58 0000000000000086 ffff81009c231000 ffffffff8000f758 Sep 28 07:49:38 www kernel: ffff81020dfd1408 0000000000000007 ffff81000a850820 ffff8102038037a0 Sep 28 07:49:38 www kernel: 00017a5bb5c6846e 000000000000861a ffff81000a850a08 0000000080009a22 Sep 28 07:49:38 www kernel: Call Trace: Sep 28 07:49:38 www kernel: [<ffffffff8000f758>] generic_permission+0x52/0xca Sep 28 07:49:38 www kernel: [<ffffffff80063c63>] __mutex_lock_slowpath+0x60/0x9b Sep 28 07:49:38 www kernel: [<ffffffff8000cea2>] do_path_lookup+0x294/0x310 Sep 28 07:49:38 www kernel: [<ffffffff80063cad>] .text.lock.mutex+0xf/0x14 Sep 28 07:49:38 www kernel: [<ffffffff8003c618>] do_unlinkat+0x66/0x141 Sep 28 07:49:38 www kernel: [<ffffffff8005d229>] tracesys+0x71/0xe0 Sep 28 07:49:40 www kernel: [<ffffffff8005d28d>] tracesys+0xd5/0xe0 Sep 28 07:49:42 www kernel: Sep 28 07:49:42 www kernel: INFO: task mysqld:24612 blocked for more than 120 seconds. Sep 28 07:49:43 www kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. Sep 28 07:49:46 www kernel: mysqld D ffff81020dfd14c0 0 24612 3266 19643 3599 (NOTLB) Sep 28 07:49:46 www kernel: ffff81019e517c78 0000000000000086 ffff81019e517c88 ffffffff80063002 Sep 28 07:49:47 www kernel: ffff810201966558 0000000000000009 ffff81015fa560c0 ffff8101c263b860 Sep 28 07:49:51 www kernel: 00017a9d113e27fe 0000000000008d5a ffff81015fa562a8 000000018006ec9f Sep 28 07:49:52 www kernel: Call Trace: Sep 28 07:49:52 www kernel: [<ffffffff80063002>] thread_return+0x62/0xfe Sep 28 07:49:52 www kernel: [<ffffffff8005a46a>] getnstimeofday+0x10/0x29 Sep 28 07:49:53 www kernel: [<ffffffff80063c63>] __mutex_lock_slowpath+0x60/0x9b Sep 28 07:49:54 www kernel: [<ffffffff80063cad>] .text.lock.mutex+0xf/0x14 Sep 28 07:49:54 www kernel: [<ffffffff8000d0b2>] do_lookup+0x90/0x1e6 Sep 28 07:49:56 www kernel: [<ffffffff8000a2e9>] __link_path_walk+0xa3a/0xfd1 Sep 28 07:50:00 www kernel: [<ffffffff8000eb8e>] link_path_walk+0x45/0xb8 Sep 28 07:50:03 www kernel: [<ffffffff8000cea2>] do_path_lookup+0x294/0x310 Sep 28 07:50:04 www kernel: [<ffffffff800129ad>] getname+0x15b/0x1c2 Sep 28 07:50:06 www kernel: [<ffffffff80023b60>] __user_walk_fd+0x37/0x4c Sep 28 07:50:06 www kernel: [<ffffffff8003f013>] vfs_lstat_fd+0x18/0x47 Sep 28 07:50:08 www kernel: [<ffffffff8002ad91>] sys_newlstat+0x19/0x31 Sep 28 07:50:10 www kernel: [<ffffffff8005d229>] tracesys+0x71/0xe0 Sep 28 07:50:15 www kernel: [<ffffffff8005d28d>] tracesys+0xd5/0xe0 Sep 28 07:50:19 www kernel: Sep 28 07:50:19 www kernel: INFO: task php:29178 blocked for more than 120 seconds. Sep 28 07:50:23 www kernel: "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. Sep 28 07:50:23 www kernel: php D 0000000000000003 0 29178 29123 (NOTLB) Sep 28 07:50:23 www kernel: ffff81004a95bdc8 0000000000000086 ffff81020dfd1408 ffffffff80009a22 Sep 28 07:50:24 www kernel: ffffffff800a2fd0 0000000000000007 ffff8101937a4040 ffff81010bde27a0 Sep 28 07:50:26 www kernel: 00017aa3a1d89c9b 000000000000d66e ffff8101937a4228 000000020e42b300 Sep 28 07:50:26 www kernel: Call Trace: Sep 28 07:50:26 www kernel: [<ffffffff80009a22>] __link_path_walk+0x173/0xfd1 Sep 28 07:50:27 www kernel: [<ffffffff800a2fd0>] wake_bit_function+0x0/0x23 Sep 28 07:50:27 www kernel: [<ffffffff8002cc58>] mntput_no_expire+0x19/0x89 Sep 28 07:50:27 www kernel: [<ffffffff8000ebf5>] link_path_walk+0xac/0xb8 Sep 28 07:50:28 www kernel: [<ffffffff80063c63>] __mutex_lock_slowpath+0x60/0x9b Sep 28 07:50:32 www kernel: [<ffffffff80023974>] __path_lookup_intent_open+0x56/0x97 Sep 28 07:50:32 www kernel: [<ffffffff80063cad>] .text.lock.mutex+0xf/0x14 Sep 28 07:50:34 www kernel: [<ffffffff8001b260>] open_namei+0xea/0x718 Sep 28 07:50:34 www kernel: [<ffffffff80067235>] do_page_fault+0x4cc/0x842 Sep 28 07:50:35 www kernel: [<ffffffff80027726>] do_filp_open+0x1c/0x38 Sep 28 07:50:35 www kernel: [<ffffffff8001a09c>] do_sys_open+0x44/0xbe Sep 28 07:50:35 www kernel: [<ffffffff8005d28d>] tracesys+0xd5/0xe0 Sep 28 07:50:35 www kernel: Sep 28 07:56:41 www kernel: proftpd invoked oom-killer: gfp_mask=0x201d2, order=0, oomkilladj=0 Sep 28 07:56:41 www kernel: Sep 28 07:56:41 www kernel: Call Trace: Sep 28 07:56:41 www kernel: [<ffffffff800c9f35>] out_of_memory+0x8e/0x2f3 Sep 28 07:56:41 www kernel: [<ffffffff800a2fa2>] autoremove_wake_function+0x0/0x2e Sep 28 07:56:41 www kernel: [<ffffffff8000f67d>] __alloc_pages+0x27f/0x308 Sep 28 07:56:41 www kernel: [<ffffffff80013047>] __do_page_cache_readahead+0x96/0x17b Sep 28 07:56:41 www kernel: [<ffffffff80013984>] filemap_nopage+0x14c/0x360 Sep 28 07:56:41 www kernel: [<ffffffff80008972>] __handle_mm_fault+0x1fd/0x103b Sep 28 07:56:41 www kernel: [<ffffffff800a4fe1>] ktime_get_ts+0x1a/0x4e Sep 28 07:56:41 www kernel: [<ffffffff80067202>] do_page_fault+0x499/0x842 Sep 28 07:56:41 www kernel: [<ffffffff8003ad91>] hrtimer_try_to_cancel+0x4a/0x53 Sep 28 07:58:10 www kernel: [<ffffffff80033541>] do_setitimer+0xd0/0x689 Sep 28 08:26:22 www syslogd 1.4.1: restart. Sep 28 08:26:22 www kernel: klogd 1.4.1, log source = /proc/kmsg started. Sep 28 08:26:22 www kernel: Linux version 2.6.18-274.17.1.el5 ([email protected]) (gcc version 4.1.2 20080704 (Red Hat 4.1.2-51)) #1 SMP Tue Jan 10 17:25:58 EST 2012 Sep 28 08:26:22 www kernel: Command line: ro root=LABEL=/

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• How long does a blocked connection from Iptables last? Is there a way to set the timeout?

  - by Josh

  iptables -A INPUT -m state --state NEW -m recent --set # If we receive more than 10 connections in 10 seconds block our friend. iptables -A INPUT -m state --state NEW -m recent --update --seconds 5 --hitcount 15 -j Log-N-Drop I have these two relevant rules from iptables. if more than 15 connections are made in 5 seconds it logs the attempt and blocks it. How long does iptables maintain the counter? Does it refresh if connections are attempted again?

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