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diff --git a/man-pages-posix-2017/man3p/semop.3p b/man-pages-posix-2017/man3p/semop.3p new file mode 100644 index 0000000..d311aa3 --- /dev/null +++ b/man-pages-posix-2017/man3p/semop.3p @@ -0,0 +1,482 @@ +'\" et +.TH SEMOP "3P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual" +.\" +.SH PROLOG +This manual page is part of the POSIX Programmer's Manual. +The Linux implementation of this interface may differ (consult +the corresponding Linux manual page for details of Linux behavior), +or the interface may not be implemented on Linux. +.\" +.SH NAME +semop +\(em XSI semaphore operations +.SH SYNOPSIS +.LP +.nf +#include <sys/sem.h> +.P +int semop(int \fIsemid\fP, struct sembuf *\fIsops\fP, size_t \fInsops\fP); +.fi +.SH DESCRIPTION +The +\fIsemop\fR() +function operates on XSI semaphores (see the Base Definitions volume of POSIX.1\(hy2017, +.IR "Section 4.17" ", " "Semaphore"). +It is unspecified whether this function interoperates with the +realtime interprocess communication facilities defined in +.IR "Section 2.8" ", " "Realtime". +.P +The +\fIsemop\fR() +function shall perform atomically a user-defined array of semaphore +operations in array order on the set of semaphores associated with the +semaphore identifier specified by the argument +.IR semid . +.P +The argument +.IR sops +is a pointer to a user-defined array of semaphore operation +structures. The implementation shall not modify elements of this array +unless the application uses implementation-defined extensions. +.P +The argument +.IR nsops +is the number of such structures in the array. +.P +Each structure, +.BR sembuf , +includes the following members: +.TS +center box tab(!); +cB | cB | cB +lw(1.25i)B | lw(1.25i)I | lw(2.5i). +Member Type!Member Name!Description +_ +unsigned short!sem_num!Semaphore number. +short!sem_op!Semaphore operation. +short!sem_flg!Operation flags. +.TE +.P +Each semaphore operation specified by +.IR sem_op +is performed on the corresponding semaphore specified by +.IR semid +and +.IR sem_num . +.P +The variable +.IR sem_op +specifies one of three semaphore operations: +.IP " 1." 4 +If +.IR sem_op +is a negative integer and the calling process has alter permission, one +of the following shall occur: +.RS 4 +.IP " *" 4 +If +.IR semval (see +.IR <sys/sem.h> ) +is greater than or equal to the absolute value of +.IR sem_op , +the absolute value of +.IR sem_op +is subtracted from +.IR semval . +Also, if (\fIsem_flg\fP &SEM_UNDO) is non-zero, the absolute value of +.IR sem_op +shall be added to the +.IR semadj +value of the calling process for the specified semaphore. +.IP " *" 4 +If +.IR semval +is less than the absolute value of +.IR sem_op +and (\fIsem_flg\fP &IPC_NOWAIT) is non-zero, +\fIsemop\fR() +shall return immediately. +.IP " *" 4 +If +.IR semval +is less than the absolute value of +.IR sem_op +and (\fIsem_flg\fP &IPC_NOWAIT) is 0, +\fIsemop\fR() +shall increment the +.IR semncnt +associated with the specified semaphore and suspend execution of the +calling thread until one of the following conditions occurs: +.RS 4 +.IP -- 4 +The value of +.IR semval +becomes greater than or equal to the absolute value of +.IR sem_op . +When this occurs, the value of +.IR semncnt +associated with the specified semaphore shall be decremented, the +absolute value of +.IR sem_op +shall be subtracted from +.IR semval +and, if (\fIsem_flg\fP &SEM_UNDO) is non-zero, the absolute value of +.IR sem_op +shall be added to the +.IR semadj +value of the calling process for the specified semaphore. +.IP -- 4 +The +.IR semid +for which the calling thread is awaiting action is removed from the +system. When this occurs, +.IR errno +shall be set to +.BR [EIDRM] +and \-1 shall be returned. +.IP -- 4 +The calling thread receives a signal that is to be caught. When this +occurs, the value of +.IR semncnt +associated with the specified semaphore shall be decremented, and the +calling thread shall resume execution in the manner prescribed in +.IR "\fIsigaction\fR\^(\|)". +.RE +.RE +.IP " 2." 4 +If +.IR sem_op +is a positive integer and the calling process has alter permission, the +value of +.IR sem_op +shall be added to +.IR semval +and, if (\fIsem_flg\fP &SEM_UNDO) is non-zero, the value of +.IR sem_op +shall be subtracted from the +.IR semadj +value of the calling process for the specified semaphore. +.IP " 3." 4 +If +.IR sem_op +is 0 and the calling process has read permission, one of the following +shall occur: +.RS 4 +.IP " *" 4 +If +.IR semval +is 0, +\fIsemop\fR() +shall return immediately. +.IP " *" 4 +If +.IR semval +is non-zero and (\fIsem_flg\fP &IPC_NOWAIT) is non-zero, +\fIsemop\fR() +shall return immediately. +.IP " *" 4 +If +.IR semval +is non-zero and (\fIsem_flg\fP &IPC_NOWAIT) is 0, +\fIsemop\fR() +shall increment the +.IR semzcnt +associated with the specified semaphore and suspend execution of the +calling thread until one of the following occurs: +.RS 4 +.IP -- 4 +The value of +.IR semval +becomes 0, at which time the value of +.IR semzcnt +associated with the specified semaphore shall be decremented. +.IP -- 4 +The +.IR semid +for which the calling thread is awaiting action is removed from the +system. When this occurs, +.IR errno +shall be set to +.BR [EIDRM] +and \-1 shall be returned. +.IP -- 4 +The calling thread receives a signal that is to be caught. When this +occurs, the value of +.IR semzcnt +associated with the specified semaphore shall be decremented, and the +calling thread shall resume execution in the manner prescribed in +.IR "\fIsigaction\fR\^(\|)". +.RE +.RE +.P +Upon successful completion, the value of +.IR sempid +for each semaphore specified in the array pointed to by +.IR sops +shall be set to the process ID of the calling process. Also, the +.IR sem_otime +timestamp shall be set to the current time, as described in +.IR "Section 2.7.1" ", " "IPC General Description". +.SH "RETURN VALUE" +Upon successful completion, +\fIsemop\fR() +shall return 0; otherwise, it shall return \-1 and set +.IR errno +to indicate the error. +.SH ERRORS +The +\fIsemop\fR() +function shall fail if: +.TP +.BR E2BIG +The value of +.IR nsops +is greater than the system-imposed maximum. +.TP +.BR EACCES +Operation permission is denied to the calling process; see +.IR "Section 2.7" ", " "XSI Interprocess Communication". +.TP +.BR EAGAIN +The operation would result in suspension of the calling process but +(\fIsem_flg\fP &IPC_NOWAIT) is non-zero. +.TP +.BR EFBIG +The value of +.IR sem_num +is greater than or equal to the number of semaphores in the set +associated with +.IR semid . +.TP +.BR EIDRM +The semaphore identifier +.IR semid +is removed from the system. +.TP +.BR EINTR +The +\fIsemop\fR() +function was interrupted by a signal. +.TP +.BR EINVAL +The value of +.IR semid +is not a valid semaphore identifier, or the number of individual +semaphores for which the calling process requests a SEM_UNDO would +exceed the system-imposed limit. +.TP +.BR ENOSPC +The limit on the number of individual processes requesting a SEM_UNDO +would be exceeded. +.TP +.BR ERANGE +An operation would cause a +.IR semval +to overflow the system-imposed limit, or an operation would cause a +.IR semadj +value to overflow the system-imposed limit. +.LP +.IR "The following sections are informative." +.SH EXAMPLES +.SS "Setting Values in Semaphores" +.P +The following example sets the values of the two semaphores associated +with the +.IR semid +identifier to the values contained in the +.IR sb +array. +.sp +.RS 4 +.nf + +#include <sys/sem.h> +\&... +int semid; +struct sembuf sb[2]; +int nsops = 2; +int result; +.P +/* Code to initialize semid. */ +\&... +.P +/* Adjust value of semaphore in the semaphore array semid. */ +sb[0].sem_num = 0; +sb[0].sem_op = -1; +sb[0].sem_flg = SEM_UNDO | IPC_NOWAIT; +sb[1].sem_num = 1; +sb[1].sem_op = 1; +sb[1].sem_flg = 0; +.P +result = semop(semid, sb, nsops); +.fi +.P +.RE +.SS "Creating a Semaphore Identifier" +.P +The following example gets a unique semaphore key using the +\fIftok\fR() +function, then gets a semaphore ID associated with that key using the +\fIsemget\fR() +function (the first call also tests to make sure the semaphore exists). +If the semaphore does not exist, the program creates it, as shown by +the second call to +\fIsemget\fR(). +In creating the semaphore for the queuing process, the program +attempts to create one semaphore with read/write permission for all. It +also uses the IPC_EXCL flag, which forces +\fIsemget\fR() +to fail if the semaphore already exists. +.P +After creating the semaphore, the program uses calls to +\fIsemctl\fR() +and +\fIsemop\fR() +to initialize it to the values in the +.IR sbuf +array. The number of processes that can execute concurrently without +queuing is initially set to 2. The final call to +\fIsemget\fR() +creates a semaphore identifier that can be used later in the program. +.P +Processes that obtain +.IR semid +without creating it check that +.IR sem_otime +is non-zero, to ensure that the creating process has completed the +\fIsemop\fR() +initialization. +.P +The final call to +\fIsemop\fR() +acquires the semaphore and waits until it is free; the SEM_UNDO option +releases the semaphore when the process exits, waiting until there are +less than two processes running concurrently. +.br +.sp +.RS 4 +.nf + +#include <stdio.h> +#include <sys/sem.h> +#include <sys/stat.h> +#include <errno.h> +#include <stdlib.h> +\&... +key_t semkey; +int semid; +struct sembuf sbuf; +union semun { + int val; + struct semid_ds *buf; + unsigned short *array; +} arg; +struct semid_ds ds; +\&... +/* Get unique key for semaphore. */ +if ((semkey = ftok("/tmp", \(aqa\(aq)) == (key_t) -1) { + perror("IPC error: ftok"); exit(1); +} +.P +/* Get semaphore ID associated with this key. */ +if ((semid = semget(semkey, 0, 0)) == -1) { +.P + /* Semaphore does not exist - Create. */ + if ((semid = semget(semkey, 1, IPC_CREAT | IPC_EXCL | S_IRUSR | + S_IWUSR | S_IRGRP | S_IWGRP | S_IROTH | S_IWOTH)) != -1) + { + /* Initialize the semaphore. */ + arg.val = 0; + sbuf.sem_num = 0; + sbuf.sem_op = 2; /* This is the number of runs without queuing. */ + sbuf.sem_flg = 0; + if (semctl(semid, 0, SETVAL, arg) == -1 + || semop(semid, &sbuf, 1) == -1) { + perror("IPC error: semop"); exit(1); + } + } + else if (errno == EEXIST) { + if ((semid = semget(semkey, 0, 0)) == -1) { + perror("IPC error 1: semget"); exit(1); + } + goto check_init; + } + else { + perror("IPC error 2: semget"); exit(1); + } +} +else +{ + /* Check that semid has completed initialization. */ + /* An application can use a retry loop at this point rather than + exiting. */ + check_init: + arg.buf = &ds; + if (semctl(semid, 0, IPC_STAT, arg) < 0) { + perror("IPC error 3: semctl"); exit(1); + } + if (ds.sem_otime == 0) { + perror("IPC error 4: semctl"); exit(1); + } +} +\&... +sbuf.sem_num = 0; +sbuf.sem_op = -1; +sbuf.sem_flg = SEM_UNDO; +if (semop(semid, &sbuf, 1) == -1) { + perror("IPC Error: semop"); exit(1); +} +.fi +.P +.RE +.SH "APPLICATION USAGE" +The POSIX Realtime Extension defines alternative interfaces for interprocess +communication. Application developers who need to use IPC should +design their applications so that modules using the IPC routines +described in +.IR "Section 2.7" ", " "XSI Interprocess Communication" +can be easily modified to use the alternative interfaces. +.SH RATIONALE +None. +.SH "FUTURE DIRECTIONS" +None. +.SH "SEE ALSO" +.IR "Section 2.7" ", " "XSI Interprocess Communication", +.IR "Section 2.8" ", " "Realtime", +.IR "\fIexec\fR\^", +.IR "\fIexit\fR\^(\|)", +.IR "\fIfork\fR\^(\|)", +.IR "\fIsemctl\fR\^(\|)", +.IR "\fIsemget\fR\^(\|)", +.IR "\fIsem_close\fR\^(\|)", +.IR "\fIsem_destroy\fR\^(\|)", +.IR "\fIsem_getvalue\fR\^(\|)", +.IR "\fIsem_init\fR\^(\|)", +.IR "\fIsem_open\fR\^(\|)", +.IR "\fIsem_post\fR\^(\|)", +.IR "\fIsem_trywait\fR\^(\|)", +.IR "\fIsem_unlink\fR\^(\|)" +.P +The Base Definitions volume of POSIX.1\(hy2017, +.IR "Section 4.17" ", " "Semaphore", +.IR "\fB<sys_ipc.h>\fP", +.IR "\fB<sys_sem.h>\fP", +.IR "\fB<sys_types.h>\fP" +.\" +.SH COPYRIGHT +Portions of this text are reprinted and reproduced in electronic form +from IEEE Std 1003.1-2017, Standard for Information Technology +-- Portable Operating System Interface (POSIX), The Open Group Base +Specifications Issue 7, 2018 Edition, +Copyright (C) 2018 by the Institute of +Electrical and Electronics Engineers, Inc and The Open Group. +In the event of any discrepancy between this version and the original IEEE and +The Open Group Standard, the original IEEE and The Open Group Standard +is the referee document. The original Standard can be obtained online at +http://www.opengroup.org/unix/online.html . +.PP +Any typographical or formatting errors that appear +in this page are most likely +to have been introduced during the conversion of the source files to +man page format. To report such errors, see +https://www.kernel.org/doc/man-pages/reporting_bugs.html . |