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/* blocked.c - generic support for blocking operations like BLPOP & WAIT.
*
* Copyright (c) 2009-2012, Salvatore Sanfilippo <antirez at gmail dot com>
* All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions are met:
*
* * Redistributions of source code must retain the above copyright notice,
* this list of conditions and the following disclaimer.
* * Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* * Neither the name of Redis nor the names of its contributors may be used
* to endorse or promote products derived from this software without
* specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
* AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
* IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
* ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
* LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
* CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
* SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
* INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
* CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
* ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
* ---------------------------------------------------------------------------
*
* API:
*
* getTimeoutFromObjectOrReply() is just an utility function to parse a
* timeout argument since blocking operations usually require a timeout.
*
* blockClient() set the CLIENT_BLOCKED flag in the client, and set the
* specified block type 'btype' filed to one of BLOCKED_* macros.
*
* unblockClient() unblocks the client doing the following:
* 1) It calls the btype-specific function to cleanup the state.
* 2) It unblocks the client by unsetting the CLIENT_BLOCKED flag.
* 3) It puts the client into a list of just unblocked clients that are
* processed ASAP in the beforeSleep() event loop callback, so that
* if there is some query buffer to process, we do it. This is also
* required because otherwise there is no 'readable' event fired, we
* already read the pending commands. We also set the CLIENT_UNBLOCKED
* flag to remember the client is in the unblocked_clients list.
*
* processUnblockedClients() is called inside the beforeSleep() function
* to process the query buffer from unblocked clients and remove the clients
* from the blocked_clients queue.
*
* replyToBlockedClientTimedOut() is called by the cron function when
* a client blocked reaches the specified timeout (if the timeout is set
* to 0, no timeout is processed).
* It usually just needs to send a reply to the client.
*
* When implementing a new type of blocking opeation, the implementation
* should modify unblockClient() and replyToBlockedClientTimedOut() in order
* to handle the btype-specific behavior of this two functions.
* If the blocking operation waits for certain keys to change state, the
* clusterRedirectBlockedClientIfNeeded() function should also be updated.
*/
#include "server.h"
/* Get a timeout value from an object and store it into 'timeout'.
* The final timeout is always stored as milliseconds as a time where the
* timeout will expire, however the parsing is performed according to
* the 'unit' that can be seconds or milliseconds.
*
* Note that if the timeout is zero (usually from the point of view of
* commands API this means no timeout) the value stored into 'timeout'
* is zero. */
int getTimeoutFromObjectOrReply(client *c, robj *object, mstime_t *timeout, int unit) {
long long tval;
if (getLongLongFromObjectOrReply(c,object,&tval,
"timeout is not an integer or out of range") != C_OK)
return C_ERR;
if (tval < 0) {
addReplyError(c,"timeout is negative");
return C_ERR;
}
if (tval > 0) {
if (unit == UNIT_SECONDS) tval *= 1000;
tval += mstime();
}
*timeout = tval;
return C_OK;
}
/* Block a client for the specific operation type. Once the CLIENT_BLOCKED
* flag is set client query buffer is not longer processed, but accumulated,
* and will be processed when the client is unblocked. */
void blockClient(client *c, int btype) {
c->flags |= CLIENT_BLOCKED;
c->btype = btype;
server.bpop_blocked_clients++;
}
/* This function is called in the beforeSleep() function of the event loop
* in order to process the pending input buffer of clients that were
* unblocked after a blocking operation. */
void processUnblockedClients(void) {
listNode *ln;
client *c;
while (listLength(server.unblocked_clients)) {
ln = listFirst(server.unblocked_clients);
serverAssert(ln != NULL);
c = ln->value;
listDelNode(server.unblocked_clients,ln);
c->flags &= ~CLIENT_UNBLOCKED;
/* Process remaining data in the input buffer, unless the client
* is blocked again. Actually processInputBuffer() checks that the
* client is not blocked before to proceed, but things may change and
* the code is conceptually more correct this way. */
if (!(c->flags & CLIENT_BLOCKED)) {
if (c->querybuf && sdslen(c->querybuf) > 0) {
processInputBuffer(c);
}
}
}
}
/* Unblock a client calling the right function depending on the kind
* of operation the client is blocking for. */
void unblockClient(client *c) {
if (c->btype == BLOCKED_LIST) {
unblockClientWaitingData(c);
} else if (c->btype == BLOCKED_WAIT) {
unblockClientWaitingReplicas(c);
} else {
serverPanic("Unknown btype in unblockClient().");
}
/* Clear the flags, and put the client in the unblocked list so that
* we'll process new commands in its query buffer ASAP. */
c->flags &= ~CLIENT_BLOCKED;
c->btype = BLOCKED_NONE;
server.bpop_blocked_clients--;
/* The client may already be into the unblocked list because of a previous
* blocking operation, don't add back it into the list multiple times. */
if (!(c->flags & CLIENT_UNBLOCKED)) {
c->flags |= CLIENT_UNBLOCKED;
listAddNodeTail(server.unblocked_clients,c);
}
}
/* This function gets called when a blocked client timed out in order to
* send it a reply of some kind. */
void replyToBlockedClientTimedOut(client *c) {
if (c->btype == BLOCKED_LIST) {
addReply(c,shared.nullmultibulk);
} else if (c->btype == BLOCKED_WAIT) {
addReplyLongLong(c,replicationCountAcksByOffset(c->bpop.reploffset));
} else {
serverPanic("Unknown btype in replyToBlockedClientTimedOut().");
}
}
/* Mass-unblock clients because something changed in the instance that makes
* blocking no longer safe. For example clients blocked in list operations
* in an instance which turns from master to slave is unsafe, so this function
* is called when a master turns into a slave.
*
* The semantics is to send an -UNBLOCKED error to the client, disconnecting
* it at the same time. */
void disconnectAllBlockedClients(void) {
listNode *ln;
listIter li;
listRewind(server.clients,&li);
while((ln = listNext(&li))) {
client *c = listNodeValue(ln);
if (c->flags & CLIENT_BLOCKED) {
addReplySds(c,sdsnew(
"-UNBLOCKED force unblock from blocking operation, "
"instance state changed (master -> slave?)\r\n"));
unblockClient(c);
c->flags |= CLIENT_CLOSE_AFTER_REPLY;
}
}
}
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