core/Lucy/Store/SharedLock.c

/* Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#define C_LUCY_SHAREDLOCK
#include "Lucy/Util/ToolSet.h"

#include <errno.h>
#include <stdio.h>
#include <ctype.h>

#include "Lucy/Store/SharedLock.h"
#include "Lucy/Store/DirHandle.h"
#include "Lucy/Store/Folder.h"
#include "Lucy/Store/OutStream.h"

SharedLock*
ShLock_new(Folder *folder, const CharBuf *name, const CharBuf *host,
           int32_t timeout, int32_t interval) {
    SharedLock *self = (SharedLock*)VTable_Make_Obj(SHAREDLOCK);
    return ShLock_init(self, folder, name, host, timeout, interval);
}

SharedLock*
ShLock_init(SharedLock *self, Folder *folder, const CharBuf *name,
            const CharBuf *host, int32_t timeout, int32_t interval) {
    LFLock_init((LockFileLock*)self, folder, name, host, timeout, interval);

    // Override.
    DECREF(self->lock_path);
    self->lock_path = (CharBuf*)INCREF(&EMPTY);

    return self;
}

bool_t
ShLock_shared(SharedLock *self) {
    UNUSED_VAR(self);
    return true;
}

bool_t
ShLock_request(SharedLock *self) {
    uint32_t i = 0;
    ShLock_request_t super_request
        = (ShLock_request_t)SUPER_METHOD(SHAREDLOCK, ShLock, Request);

    // EMPTY lock_path indicates whether this particular instance is locked.
    if (self->lock_path != (CharBuf*)&EMPTY
        && Folder_Exists(self->folder, self->lock_path)
       ) {
        // Don't allow double obtain.
        Err_set_error((Err*)LockErr_new(CB_newf("Lock already obtained via '%o'",
                                                self->lock_path)));
        return false;
    }

    DECREF(self->lock_path);
    self->lock_path = CB_new(CB_Get_Size(self->name) + 10);
    do {
        CB_setf(self->lock_path, "locks/%o-%u32.lock", self->name, ++i);
    } while (Folder_Exists(self->folder, self->lock_path));

    bool_t success = super_request(self);
    if (!success) { ERR_ADD_FRAME(Err_get_error()); }
    return success;
}

void
ShLock_release(SharedLock *self) {
    if (self->lock_path != (CharBuf*)&EMPTY) {
        ShLock_release_t super_release
            = (ShLock_release_t)SUPER_METHOD(SHAREDLOCK, ShLock, Release);
        super_release(self);

        // Empty out lock_path.
        DECREF(self->lock_path);
        self->lock_path = (CharBuf*)INCREF(&EMPTY);
    }
}


void
ShLock_clear_stale(SharedLock *self) {
    DirHandle *dh;
    CharBuf   *entry;
    CharBuf   *candidate = NULL;
    CharBuf   *lock_dir_name = (CharBuf*)ZCB_WRAP_STR("locks", 5);

    if (Folder_Find_Folder(self->folder, lock_dir_name)) {
        dh = Folder_Open_Dir(self->folder, lock_dir_name);
        if (!dh) { RETHROW(INCREF(Err_get_error())); }
        entry = DH_Get_Entry(dh);
    }
    else {
        return;
    }

    // Take a stab at any file that begins with our lock name.
    while (DH_Next(dh)) {
        if (CB_Starts_With(entry, self->name)
            && CB_Ends_With_Str(entry, ".lock", 5)
           ) {
            candidate = candidate ? candidate : CB_new(0);
            CB_setf(candidate, "%o/%o", lock_dir_name, entry);
            ShLock_Maybe_Delete_File(self, candidate, false, true);
        }
    }

    DECREF(candidate);
    DECREF(dh);
}

bool_t
ShLock_is_locked(SharedLock *self) {
    DirHandle *dh;
    CharBuf   *entry;

    CharBuf *lock_dir_name = (CharBuf*)ZCB_WRAP_STR("locks", 5);
    if (Folder_Find_Folder(self->folder, lock_dir_name)) {
        dh = Folder_Open_Dir(self->folder, lock_dir_name);
        if (!dh) { RETHROW(INCREF(Err_get_error())); }
        entry = DH_Get_Entry(dh);
    }
    else {
        return false;
    }

    while (DH_Next(dh)) {
        // Translation:  $locked = 1 if $entry =~ /^\Q$name-\d+\.lock$/
        if (CB_Starts_With(entry, self->name)
            && CB_Ends_With_Str(entry, ".lock", 5)
           ) {
            ZombieCharBuf *scratch = ZCB_WRAP(entry);
            ZCB_Chop(scratch, sizeof(".lock") - 1);
            while (isdigit(ZCB_Code_Point_From(scratch, 1))) {
                ZCB_Chop(scratch, 1);
            }
            if (ZCB_Code_Point_From(scratch, 1) == '-') {
                ZCB_Chop(scratch, 1);
                if (ZCB_Equals(scratch, (Obj*)self->name)) {
                    DECREF(dh);
                    return true;
                }
            }
        }
    }

    DECREF(dh);
    return false;
}