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/*
* Course data structures and locking
*
* Copyright (C) 2024 Runxi Yu <https://runxiyu.org>
* SPDX-License-Identifier: AGPL-3.0-or-later
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU Affero General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU Affero General Public License for more details.
*
* You should have received a copy of the GNU Affero General Public License
* along with this program. If not, see <https://www.gnu.org/licenses/>.
*/
package main
import (
"context"
"fmt"
"log/slog"
"sync"
"sync/atomic"
"github.com/coder/websocket"
)
type courseT struct {
/*
* Selected is usually accessed atomically, but a lock is still
* necessary as we need to sequentialize compare-with-Max-and-increment
* operations.
* We put Selected before other values to ensure 64-bit alignment on
* all systems, because it needs to be accessed atomically. See the
* "Bugs" section of sync/atomic.
*/
Selected uint32 /* atomic */
SelectedLock sync.Mutex
ID int
Max uint32
Title string
Type string
Group string
Teacher string
Location string
CourseID string
SectionID string
Usems sync.Map /* string, *usemT */
}
var courses sync.Map /* int, *courseT */
var numCourses uint32 /* atomic */
const staffDepartment = "Staff"
/*
* Read course information from the database. This should be called during
* setup.
*/
func setupCourses(ctx context.Context) error {
rows, err := db.Query(
ctx,
"SELECT id, nmax, title, ctype, cgroup, teacher, location, course_id, section_id FROM courses",
)
if err != nil {
return wrapError(errUnexpectedDBError, err)
}
for {
if !rows.Next() {
err := rows.Err()
if err != nil {
return wrapError(
errUnexpectedDBError,
err,
)
}
break
}
currentCourse := courseT{} //exhaustruct:ignore
err = rows.Scan(
¤tCourse.ID,
¤tCourse.Max,
¤tCourse.Title,
¤tCourse.Type,
¤tCourse.Group,
¤tCourse.Teacher,
¤tCourse.Location,
¤tCourse.CourseID,
¤tCourse.SectionID,
)
if err != nil {
return wrapError(errUnexpectedDBError, err)
}
if !checkCourseType(currentCourse.Type) {
return fmt.Errorf(
"%w: %d %s",
errInvalidCourseType,
currentCourse.ID,
currentCourse.Type,
)
}
if !checkCourseGroup(currentCourse.Group) {
return fmt.Errorf(
"%w: %d %s",
errInvalidCourseGroup,
currentCourse.ID,
currentCourse.Group,
)
}
err := db.QueryRow(
ctx,
"SELECT COUNT (*) FROM choices WHERE courseid = $1",
currentCourse.ID,
).Scan(¤tCourse.Selected)
if err != nil {
return wrapError(
errUnexpectedDBError,
err,
)
}
courses.Store(currentCourse.ID, ¤tCourse)
atomic.AddUint32(&numCourses, 1)
}
return nil
}
func (course *courseT) decrementSelectedAndPropagate(
ctx context.Context,
conn *websocket.Conn,
) error {
func() {
course.SelectedLock.Lock()
defer course.SelectedLock.Unlock()
atomic.AddUint32(&course.Selected, ^uint32(0))
}()
go func() {
defer func() {
if e := recover(); e != nil {
slog.Error("panic", "arg", e)
}
}()
propagateSelectedUpdate(course)
}()
err := sendSelectedUpdate(ctx, conn, course.ID)
if err != nil {
return wrapError(
errCannotSend,
err,
)
}
return nil
}
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