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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"
"sync"
)
type coursetypeT string
type courseT struct {
ID int
Selected int
SelectedLock sync.RWMutex
Max int
Title string
Type coursetypeT
Teacher string
Location string
}
/*
* const (
* sport coursetypeT = "Sport"
* enrichment coursetypeT = "Enrichment"
* culture coursetypeT = "Culture"
* )
*/
/*
* The courses are simply stored in a map indexed by the course ID, although
* the course struct itself also contains an ID field. A lock is embedded
* inside the struct; we use a lock here instead of a pointer to a lock as
* it would be easy to forget to initialize the lock when creating the
* struct. However, this means that the struct could not be copied (though
* this should only ever happen during creation anyways), therefore we use a
* pointer to the struct as the value of the map, instead of the struct itself.
*/
var courses map[int](*courseT)
/*
* This RWMutex is only for massive modifications of the course struct, since
* locking it on every write would be inefficient; in normal operation the only
* write that could occur to the courses struct is changing the Selected
* number, which should be handled with courseT.SelectedLock.
*/
var coursesLock sync.RWMutex
/*
* Read course information from the database. This should be called during
* setup. Failure to do so before accessing course information may lead to
* a null pointer dereference.
*/
func setupCourses() error {
coursesLock.Lock()
defer coursesLock.Unlock()
courses = make(map[int](*courseT))
rows, err := db.Query(
context.Background(),
"SELECT id, nmax, title, ctype, teacher, location FROM courses",
)
if err != nil {
return fmt.Errorf("error fetching courses: %w", err)
}
for {
if !rows.Next() {
err := rows.Err()
if err != nil {
return fmt.Errorf("error fetching courses: %w", err)
}
break
}
currentCourse := courseT{} //exhaustruct:ignore
err = rows.Scan(
¤tCourse.ID,
¤tCourse.Max,
¤tCourse.Title,
¤tCourse.Type,
¤tCourse.Teacher,
¤tCourse.Location,
)
if err != nil {
return fmt.Errorf("error fetching courses: %w", err)
}
err := db.QueryRow(context.Background(),
"SELECT COUNT (*) FROM choices WHERE courseid = $1",
currentCourse.ID,
).Scan(¤tCourse.Selected)
if err != nil {
return fmt.Errorf("error querying course member number: %w", err)
}
courses[currentCourse.ID] = ¤tCourse
}
return nil
}
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