Xinu7/man/man2/Intro2.2

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Section 2: System Calls
.IX "system call"
.SX "Xinu" "system calls"
.sp 3
.ps 10
.PP
The Xinu operating system kernel consists of a set of run-time procedures
to implement operating system services on an LSI 11/2 microcomputer.
The system supports multiple processes, I/O, synchronization
based on counting semaphores, preemptive scheduling, and
communication with other machines.
Each page in this section describes a system routine that can be
called by a user process.
.PP
Each page describes one system call,
giving the number and types of arguments
that must be passed to the procedure under the
heading "SYNOPSIS"
(by giving their declaration
in C syntax).
The heading "SEE ALSO" suggests the names of other system
calls that may be related to the described function.
For example, the "SEE ALSO" entry for system call \f2wait\f1
suggests that the programmer may want to look at
the page for \f2signal\f1 because both routines operate on
semaphores.
.PP
In general, Xinu blocks processes when requested services are
not available.
Unless the manual page suggests otherwise, the programmer should
assume that the process requesting system services may be delayed
until the request can be satisfied.
For example, calling \f2read\f1 may cause an arbitrary delay until
data can be obtained from the device.