Semaphore
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guten morgen
hab folgende frage und zwar existieren unter Linux Semaphore, die man in C++ Programmen verwenden kann. Mit welchen Befehlen kann man sie erzeugen, initialisieren, zerstören.
danke für eure hilfe
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Moin Moin
man 2 semget
Eine abstrakte Klasse dafür, die sich darüber legt und C++ ist, ist u.a. in der CommonC++ Lib zu finden.
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wenn ich man 2 semget eingebe kommt die antwort
kein manual-eintrag für semget vorhanden in sektion 2kannst du mir nicht mal den teil kopieren (wenn er nicht zu gross ist)
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Hier bitte sehr die Ausgabe von "man 2 semget"
SEMGET(2) Linux Programmer's Manual SEMGET(2) NAME semget - get a semaphore set identifier SYNOPSIS # include <sys/types.h> # include <sys/ipc.h> # include <sys/sem.h> int semget ( key_t key, int nsems, int semflg ) DESCRIPTION The function returns the semaphore set identifier associated to the value of the argument key. A new set of nsems semaphores is created if key has value IPC_PRI VATE or key isn't IPC_PRIVATE, no existing semaphore set is associated to key, and IPC_CREAT is asserted in semflg (i.e. semflg & IPC_CREAT isn't zero). The pres ence in semflg of the fields IPC_CREAT and IPC_EXCL plays the same role, with respect to the existence of the semaphore set, as the presence of O_CREAT and O_EXCL in the mode argument of the open(2) system call: i.e. the semget function fails if semflg asserts both IPC_CREAT and IPC_EXCL and a semaphore set already exists for key. Upon creation, the lower 9 bits of the argument semflg define the access permis sions (for owner, group and others) to the semaphore set in the same format, and with the same meaning, as for the access permissions parameter in the open(2) or creat(2) system calls (though the execute permissions are not used by the system, and write permissions, for a semaphore set, effectively means alter permissions). Furthermore, while creating, the system call initializes the system semaphore set data structure semid_ds as follows: sem_perm.cuid and sem_perm.uid are set to the effective user-ID of the call ing process. sem_perm.cgid and sem_perm.gid are set to the effective group-ID of the calling process. The lowest order 9 bits of sem_perm.mode are set to the lowest order 9 bit of semflg. sem_nsems is set to the value of nsems. sem_otime is set to 0. sem_ctime is set to the current time. The argument nsems can be 0 (a don't care) when the system call isn't a create one. Otherwise nsems must be greater than 0 and less or equal to the maximum number of semaphores per semid, (SEMMSL). If the semaphore set already exists, the access permissions are verified, and a check is made to see if it is marked for destruction. RETURN VALUE If successful, the return value will be the semaphore set identifier (a positive integer), otherwise -1 with errno indicating the error. ERRORS For a failing return, errno will be set to one among the following values: EACCES A semaphore set exists for key, but the calling process has no access permissions to the set. EEXIST A semaphore set exists for key and semflg was asserting both IPC_CREAT and IPC_EXCL. EIDRM The semaphore set is marked as to be deleted. ENOENT No semaphore set exists for key and semflg wasn't asserting IPC_CREAT. ENOMEM A semaphore set has to be created but the system has not enough memory for the new data structure. ENOSPC A semaphore set has to be created but the system limit for the maximum number of semaphore sets (SEMMNI), or the system wide maximum number of semaphores (SEMMNS), would be exceeded. NOTES IPC_PRIVATE isn't a flag field but a key_t type. If this special value is used for key, the system call ignores everything but the lowest order 9 bits of semflg and creates a new semaphore set (on success). The followings are limits on semaphore set resources affecting a semget call: SEMMNI System wide maximum number of semaphore sets: policy dependent. SEMMSL Maximum number of semaphores per semid: implementation dependent (500 currently). SEMMNS System wide maximum number of semaphores: policy dependent. Values greater than SEMMSL * SEMMNI makes it irrelevant. BUGS Use of IPC_PRIVATE doesn't inhibit to other processes the access to the allocated semaphore set. As for the files, there is currently no intrinsic way for a process to ensure exclusive access to a semaphore set. Asserting both IPC_CREAT and IPC_EXCL in sem flg only ensures (on success) that a new semaphore set will be created, it doesn't imply exclusive access to the semaphore set. The data structure associated with each semaphore in the set isn't initialized by the system call. In order to initialize those data structures, one has to execute a subsequent call to semctl(2) to perform a SETVAL or a SETALL command on the semaphore set. CONFORMING TO SVr4, SVID. SVr4 documents additional error conditions EINVAL, EFBIG, E2BIG, EAGAIN, ERANGE, EFAULT. SEE ALSO ftok(3), ipc(5), semctl(2), semop(2) Linux 0.99.13 1993-11-01 SEMGET(2)
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Manpages findest du auch online z.B. unter:
http://www.freebsd.org/cgi/man.cgi?manpath=Red+Hat+Linux%2Fi386+7.3&format=html
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kann mir jemand die befehle sem_wait , sem_trywait und sem_post erklären in der man sind sie nicht drin und bei google hab ich bis jetzt nichts gescheites gefunden
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Wieso nichts gescheites gefunden?
mit "man irgendwas" im google auch nicht
?
z.B.
http://www.st.carnet.hr/cgi-bin/man-cgi?sem_wait+3
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@solaris
danke, ist halt so ne sache mit google
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@stef
> @solaris
> danke, ist halt so ne sache mit google
dazu brauchts kein GoogelWenn du meinen Link gefolgt wärest hättest du nur mit dem Pull-Down-Menü ein bisschen spielen müssen:
FreeBSD 5.0-current
http://www.freebsd.org/cgi/man.cgi?query=sem_wait&apropos=0&sektion=0&manpath=SunOS+5.8&format=html
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@descartes
erstmals danke für deine hilfe.
da ich Suse linux verwende und ich unter diesem punkt nichts gefunden hab dachte ich das es vielleicht nicht aktuell ist.