{"id":96138,"date":"2020-10-08T19:42:26","date_gmt":"2020-10-08T17:42:26","guid":{"rendered":"https:\/\/prohoster.info\/blog\/administrirovanie\/znakomimsya-s-semaforami-v-linux"},"modified":"2020-10-08T19:42:26","modified_gmt":"2020-10-08T17:42:26","slug":"znakomimsya-s-semaforami-v-linux","status":"publish","type":"post","link":"https:\/\/prohoster.info\/cs\/blog\/administrirovanie\/znakomimsya-s-semaforami-v-linux","title":{"rendered":"Seznamujeme se se semafory v Linuxu","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"<p><b><i>P\u0159eklad \u010dl\u00e1nku byl vyhotoven p\u0159ed za\u010d\u00e1tkem kurzu <noindex><a rel=\"nofollow\" href=\"https:\/\/otus.pw\/kRX0\/\">\u201eAdministrator Linux.Basic\u201c<\/a><\/noindex>.<\/p>\n<p><img decoding=\"async\" alt=\"Seznamujeme se se semafory v Linuxu\" src=\"\/wp-content\/uploads\/2020\/10\/93604a8804db099834e873de072cbfc9.jpg\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<br \/>\n<\/i><\/b><\/p>\n<p>Semafor je mechanismus, kter\u00fd umo\u017e\u0148uje konkuruj\u00edc\u00edm proces\u016fm a vl\u00e1kn\u016fm pracovat se sd\u00edlen\u00fdmi zdroji a pom\u00e1h\u00e1 \u0159e\u0161it r\u016fzn\u00e9 probl\u00e9my synchronizace, jako jsou z\u00e1vody, deadlocky (vz\u00e1jemn\u00e9 blokace) a nespr\u00e1vn\u00e9 chov\u00e1n\u00ed vl\u00e1ken.<\/p>\n<p>Pro \u0159e\u0161en\u00ed t\u011bchto probl\u00e9m\u016f j\u00e1dro obsahuje prost\u0159edky jako mutexy, semafory, sign\u00e1ly a bari\u00e9ry.<\/p>\n<p>Existuj\u00ed t\u0159i typy semafor\u016f:<\/p>\n<ol>\n<li>Bin\u00e1rn\u00ed semafory (binary semaphore)<\/li>\n<li>Semafory-\u010d\u00edsla (counting semaphore)<\/li>\n<li>Aplikace semafor\u016f (semaphore set)<\/li>\n<\/ol>\n<p><noindex><a rel=\"nofollow\" name=\"habracut\"><\/a><\/noindex><\/p>\n<h3>Zobrazen\u00ed stavu IPC<\/h3>\n<p>\nPomoc\u00ed n\u00ed\u017ee uveden\u00fdch p\u0159\u00edkaz\u016f m\u016f\u017eete z\u00edskat informace o aktu\u00e1ln\u00edm stavu prost\u0159edk\u016f meziprocesov\u00e9 komunikace (inter-process communication, IPC).<\/p>\n<pre><code class=\"bash\"># ipcs\n------ Shared Memory Segments --------\nkey shmid owner perms bytes nattch status\n0x00000000 65536 root 600 393216 2 dest\n0x00000000 98305 root 600 393216 2 dest\n0x00000000 131074 root 600 393216 2 dest\n0x00000000 163843 root 600 393216 2 dest\n0x00000000 196612 root 600 393216 2 dest\n0x00000000 229381 root 600 393216 2 dest\n0x00000000 262150 root 600 393216 2 dest\n0x00000000 294919 root 600 393216 2 dest\n0x00000000 327688 root 600 393216 2 dest\n------ Semaphore Arrays --------\n\nkey semid owner perms nsems\n\n------ Message Queues --------\nkey msqid owner perms used-bytes messages<\/code><\/pre>\n<p><\/p>\n<h3>Aktivn\u00ed aplikace semafor\u016f<\/h3>\n<p>\nZobrazen\u00ed informac\u00ed o aktivn\u00edch aplikac\u00edch semafor\u016f.<\/p>\n<pre><code class=\"bash\"># ipcs -s\n------ Semaphore Arrays --------\nkey semid owner perms nsems<\/code><\/pre>\n<p><\/p>\n<h3>Segmenty sd\u00edlen\u00e9 pam\u011bti<\/h3>\n<p>\nZobrazen\u00ed informac\u00ed o aktivn\u00edch segmentech sd\u00edlen\u00e9 pam\u011bti.<\/p>\n<pre><code class=\"bash\"># ipcs -m\n------ Shared Memory Segments --------\nkey shmid owner perms bytes nattch status\n0x00000000 65536 root 600 393216 2 dest\n0x00000000 98305 root 600 393216 2 dest<\/code><\/pre>\n<p><\/p>\n<h3>Limity<\/h3>\n<p>\nT\u00fdm <code>ipcs -l<\/code> zobrazuje limity sd\u00edlen\u00e9 pam\u011bti, semafor\u016f a zpr\u00e1v.<\/p>\n<pre><code class=\"bash\"># ipcs -l\n------ Shared Memory Limits --------\nmax number of segments = 4096\nmax seg size (kbytes) = 4194303\nmax total shared memory (kbytes) = 1073741824\nmin seg size (bytes) = 1\n\n------ Semaphore Limits --------\nmax number of arrays = 128\nmax semaphores per array = 250\nmax semaphores system wide = 32000\nmax ops per semop call = 32\nsemaphore max value = 32767\n\n------ Messages: Limits --------\nmax queues system wide = 16\nmax size of message (bytes) = 65536\ndefault max size of queue (bytes) = 65536<\/code><\/pre>\n<p><\/p>\n<h3>Sd\u00edlen\u00e1 pam\u011b\u0165<\/h3>\n<p>\nN\u00ed\u017ee uveden\u00fd p\u0159\u00edkaz zobrazuje sd\u00edlenou pam\u011b\u0165.<\/p>\n<pre><code class=\"bash\"># ipcs -m\n------ Shared Memory Segments --------\nkey shmid owner perms bytes nattch status\n0x00000000 65536 root 600 393216 2 dest\n0x00000000 98305 root 600 393216 2 dest\n0x00000000 131074 root 600 393216 2 dest\n0x00000000 163843 root 600 393216 2 dest\n0x00000000 196612 root 600 393216 2 dest\n0x00000000 229381 root 600 393216 2 dest\n0x00000000 262150 root 600 393216 2 dest\n0x00000000 294919 root 600 393216 2 dest\n0x00000000 327688 root 600 393216 2 dest<\/code><\/pre>\n<p><\/p>\n<h3>Tv\u016frci zdroj\u016f<\/h3>\n<p>\nP\u0159\u00edkaz zobrazuje u\u017eivatele a skupinu vlastn\u00edka a tv\u016frce zdroje.<\/p>\n<pre><code class=\"bash\"># ipcs -m -c\n\n------ Shared Memory Segment Creators\/Owners --------\nshmid perms cuid cgid uid gid\n65536 600 root root root root\n98305 600 root root root root\n131074 600 root root root root\n163843 600 root root root root\n196612 600 root root root root\n229381 600 root root root root\n262150 600 root root root root\n294919 600 root root root root\n327688 600 root root root root<\/code><\/pre>\n<p><\/p>\n<h3>Vyu\u017eit\u00ed prost\u0159edk\u016f IPC<\/h3>\n<p>\nV p\u0159\u00edkladu uveden\u00e9m n\u00ed\u017ee parametr <code>-u<\/code> zobrazuje shrnut\u00ed o pou\u017eit\u00ed v\u0161ech prost\u0159edk\u016f IPC.<\/p>\n<pre><code class=\"bash\"># ipcs -u\n\n------ Shared Memory Status --------\nsegments allocated 9\npages allocated 864\npages resident 477\npages swapped 0\nSwap performance: 0 attempts 0 successes\n\n------ Semaphore Status --------\nused arrays = 0\nallocated semaphores = 0\n\n------ Messages: Status --------\nallocated queues = 0\nused headers = 0\nused space = 0 bytes<\/code><\/pre>\n<p>\nP\u0159i zastaven\u00ed slu\u017eeb by m\u011bly b\u00fdt tak\u00e9 odstran\u011bny semafory a segmenty sd\u00edlen\u00e9 pam\u011bti. Pokud nejsou odstran\u011bny, lze je odstranit pomoc\u00ed p\u0159\u00edkazu ipcrm, p\u0159ed\u00e1n\u00edm identifik\u00e1toru IPC-objektu.<\/p>\n<pre><code class=\"bash\"># ipcs -a\n# ipcrm -s &lt; sem id&gt;<\/code><\/pre>\n<p>\nLimity semafor\u016f je tak\u00e9 mo\u017en\u00e9 upravit pomoc\u00ed <code>sysctl<\/code>.<\/p>\n<pre><code class=\"bash\"># \/sbin\/sysctl -w kernel.sem=250\n<\/code><\/pre>\n<p>\n<noindex><a rel=\"nofollow\" href=\"https:\/\/otus.pw\/kRX0\/\"><img decoding=\"async\" alt=\"Seznamujeme se se semafory v Linuxu\" src=\"\/wp-content\/uploads\/2020\/10\/e9f6606dbef02ed0dd83662ed9b40015.jpg\" style=\"display:block;margin: 0 auto;\" \/><\/a><\/noindex><br \/>\n<br \/>Zdroj: <a content=\"nofollow\" rel=\"nofollow\" href=\"https:\/\/habr.com\/ru\/company\/otus\/blog\/522418\/\">habr.com<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"<p>\u041f\u0435\u0440\u0435\u0432\u043e\u0434 \u0441\u0442\u0430\u0442\u044c\u0438 \u043f\u043e\u0434\u0433\u043e\u0442\u043e\u0432\u043b\u0435\u043d \u0432 \u043f\u0440\u0435\u0434\u0434\u0432\u0435\u0440\u0438\u0438 \u0441\u0442\u0430\u0440\u0442\u0430 \u043a\u0443\u0440\u0441\u0430 \u00abAdministrator Linux.Basic\u00bb. \u0421\u0435\u043c\u0430\u0444\u043e\u0440 \u2013 \u044d\u0442\u043e \u043c\u0435\u0445\u0430\u043d\u0438\u0437\u043c, \u043a\u043e\u0442\u043e\u0440\u044b\u0439 \u043f\u043e\u0437\u0432\u043e\u043b\u044f\u0435\u0442 \u043a\u043e\u043d\u043a\u0443\u0440\u0438\u0440\u0443\u044e\u0449\u0438\u043c \u043f\u0440\u043e\u0446\u0435\u0441\u0441\u0430\u043c \u0438 \u043f\u043e\u0442\u043e\u043a\u0430\u043c \u0440\u0430\u0431\u043e\u0442\u0430\u0442\u044c \u0441 \u043e\u0431\u0449\u0438\u043c\u0438 \u0440\u0435\u0441\u0443\u0440\u0441\u0430\u043c\u0438 \u0438 \u043f\u043e\u043c\u043e\u0433\u0430\u0435\u0442 \u0432 \u0440\u0435\u0448\u0435\u043d\u0438\u0438 \u0440\u0430\u0437\u043b\u0438\u0447\u043d\u044b\u0445 \u043f\u0440\u043e\u0431\u043b\u0435\u043c \u0441\u0438\u043d\u0445\u0440\u043e\u043d\u0438\u0437\u0430\u0446\u0438\u0438 \u0442\u0430\u043a\u0438\u0445 \u043a\u0430\u043a \u0433\u043e\u043d\u043a\u0438, \u0434\u0435\u0434\u043b\u043e\u043a\u0438 (\u0432\u0437\u0430\u0438\u043c\u043d\u044b\u0435 \u0431\u043b\u043e\u043a\u0438\u0440\u043e\u0432\u043a\u0438) \u0438 \u043d\u0435\u043f\u0440\u0430\u0432\u0438\u043b\u044c\u043d\u043e\u0435 \u043f\u043e\u0432\u0435\u0434\u0435\u043d\u0438\u0435 \u043f\u043e\u0442\u043e\u043a\u043e\u0432. \u0414\u043b\u044f \u0440\u0435\u0448\u0435\u043d\u0438\u044f \u044d\u0442\u0438\u0445 \u043f\u0440\u043e\u0431\u043b\u0435\u043c \u0432 \u044f\u0434\u0440\u0435 \u043f\u0440\u0438\u0441\u0443\u0442\u0441\u0442\u0432\u0443\u044e\u0442 \u0442\u0430\u043a\u0438\u0435 \u0441\u0440\u0435\u0434\u0441\u0442\u0432\u0430 \u043a\u0430\u043a \u043c\u044c\u044e\u0442\u0435\u043a\u0441\u044b, \u0441\u0435\u043c\u0430\u0444\u043e\u0440\u044b, \u0441\u0438\u0433\u043d\u0430\u043b\u044b \u0438 \u0431\u0430\u0440\u044c\u0435\u0440\u044b. 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