{"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\/nl\/blog\/administrirovanie\/znakomimsya-s-semaforami-v-linux","title":{"rendered":"Laten we semaforen in Linux verkennen","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"<p><b><i>De vertaling van het artikel is voorbereid ter voorbereiding op de start van de cursus <noindex><a rel=\"nofollow\" href=\"https:\/\/otus.pw\/kRX0\/\">\u00abAdministrator Linux.Basic\u00bb<\/a><\/noindex>.<\/p>\n<p><img decoding=\"async\" alt=\"Laten we semaforen in Linux verkennen\" src=\"\/wp-content\/uploads\/2020\/10\/93604a8804db099834e873de072cbfc9.jpg\" style=\"display:block;margin: 0 auto;\" \/><br \/>\n<br \/>\n<\/i><\/b><\/p>\n<p>Een semafoor is een mechanisme dat concurrente processen en threads in staat stelt om met gedeelde bronnen te werken en helpt bij het oplossen van verschillende synchronisatieproblemen zoals racecondities, deadlocks (wederzijdse blokkeringen) en onjuist gedrag van threads.<\/p>\n<p>Om deze problemen op te lossen zijn er in de kernel middelen aanwezig zoals mutexen, semaforen, signalen en barri\u00e8res.<\/p>\n<p>Er zijn drie soorten semaforen:<\/p>\n<ol>\n<li>Binaire semaforen (binary semaphore)<\/li>\n<li>Teller-semafory (counting semaphore)<\/li>\n<li>Semaphore arrays (semaphore set)<\/li>\n<\/ol>\n<p><noindex><a rel=\"nofollow\" name=\"habracut\"><\/a><\/noindex><\/p>\n<h3>Bekijk de status van IPC<\/h3>\n<p>\nMet de onderstaande commando's kunt u informatie krijgen over de huidige status van inter-process communicatie (IPC) middelen.<\/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>Actieve semafoor arrays<\/h3>\n<p>\nOverzicht van informatie over actieve semafoor arrays.<\/p>\n<pre><code class=\"bash\"># ipcs -s\n------ Semaphore Arrays --------\nkey semid owner perms nsems<\/code><\/pre>\n<p><\/p>\n<h3>Segmenten van gedeelde geheugen<\/h3>\n<p>\nBekijk informatie over actieve gedeelde geheugen segmenten.<\/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>Limieten<\/h3>\n<p>\nOpdracht <code>ipcs -l<\/code> toont de limieten van gedeeld geheugen, semaforen en berichten.<\/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>Gedeeld geheugen<\/h3>\n<p>\nHet onderstaande commando toont het gedeelde geheugen.<\/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>Resourcecreators<\/h3>\n<p>\nDit commando toont de gebruiker en groep van de eigenaar en creator van de resource.<\/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>Gebruik van IPC middelen<\/h3>\n<p>\nIn het onderstaande voorbeeld toont de parameter <code>-u<\/code> een samenvatting van het gebruik van alle IPC middelen.<\/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>\nBij het stoppen van diensten moeten semaforen en gedeelde geheugen segmenten ook worden verwijderd. Als ze niet worden verwijderd, kan dit worden gedaan met het commando ipcrm, door de ID van het IPC-object door te geven.<\/p>\n<pre><code class=\"bash\"># ipcs -a\n# ipcrm -s &lt; sem id&gt;<\/code><\/pre>\n<p>\nHet is ook mogelijk om de limieten van semaforen te wijzigen met <code>, beschikbaar zijn voor<\/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=\"Laten we semaforen in Linux verkennen\" src=\"\/wp-content\/uploads\/2020\/10\/e9f6606dbef02ed0dd83662ed9b40015.jpg\" style=\"display:block;margin: 0 auto;\" \/><\/a><\/noindex><br \/>\n<br \/>Bron: <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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