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Hopefully improve commenting of #5126.

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Reading the PR gave me the opportunity to better specify what the code
was doing in places where I was not immediately sure about what was
going on. Moreover I documented the structure in server.h so that people
reading the header file will immediately understand what the structure
is useful for.
This commit is contained in:
antirez 2018-07-16 17:56:54 +02:00
parent e22a1218bc
commit f9c84d6d39
2 changed files with 22 additions and 10 deletions
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30
src/networking.c
View File

@ -245,12 +245,15 @@ void _addReplyStringToList(client *c, const char *s, size_t len) {
listNode *ln = listLast(c->reply);
clientReplyBlock *tail = ln? listNodeValue(ln): NULL;
/* It is possible that we have a tail list node, but no tail buffer.
* if addDeferredMultiBulkLength() was used. */
/* Note that 'tail' may be NULL even if we have a tail node, becuase when
* addDeferredMultiBulkLength() is used, it sets a dummy node to NULL just
* fo fill it later, when the size of the bulk length is set. */
/* Append to tail string when possible. */
if (tail) {
/* Copy the part we can fit into the tail, and leave the rest for a new node */
/* Copy the part we can fit into the tail, and leave the rest for a
* new node */
size_t avail = tail->size - tail->used;
size_t copy = avail >= len? len: avail;
memcpy(tail->buf + tail->used, s, copy);
@ -259,7 +262,8 @@ void _addReplyStringToList(client *c, const char *s, size_t len) {
len -= copy;
}
if (len) {
/* Create a new node, make sure it is allocated to at least PROTO_REPLY_CHUNK_BYTES */
/* Create a new node, make sure it is allocated to at
* least PROTO_REPLY_CHUNK_BYTES */
size_t size = len < PROTO_REPLY_CHUNK_BYTES? PROTO_REPLY_CHUNK_BYTES: len;
tail = zmalloc(size + sizeof(clientReplyBlock));
/* take over the allocation's internal fragmentation */
@ -408,11 +412,17 @@ void setDeferredMultiBulkLength(client *c, void *node, long length) {
if (node == NULL) return;
serverAssert(!listNodeValue(ln));
/* Glue into next node when:
* - the next node is non-NULL,
* - it has enough room already allocated
* - and not too large (avoid large memmove) */
if (ln->next != NULL && (next = listNodeValue(ln->next)) &&
/* Normally we fill this dummy NULL node, added by addDeferredMultiBulkLength(),
* with a new buffer structure containing the protocol needed to specify
* the length of the array following. However sometimes when there is
* little memory to move, we may instead remove this NULL node, and prefix
* our protocol in the node immediately after to it, in order to save a
* write(2) syscall later. Conditions needed to do it:
*
* - The next node is non-NULL,
* - It has enough room already allocated
* - And not too large (avoid large memmove) */
if (ln->next != NULL && (next = listNodeValue(ln->next)) &&
next->size - next->used >= lenstr_len &&
next->used < PROTO_REPLY_CHUNK_BYTES * 4) {
memmove(next->buf + lenstr_len, next->buf, next->used);
@ -422,7 +432,7 @@ void setDeferredMultiBulkLength(client *c, void *node, long length) {
} else {
/* Create a new node */
clientReplyBlock *buf = zmalloc(lenstr_len + sizeof(clientReplyBlock));
/* take over the allocation's internal fragmentation */
/* Take over the allocation's internal fragmentation */
buf->size = zmalloc_usable(buf) - sizeof(clientReplyBlock);
buf->used = lenstr_len;
memcpy(buf->buf, lenstr, lenstr_len);

2
src/server.h
View File

@ -619,6 +619,8 @@ typedef struct redisObject {
struct evictionPoolEntry; /* Defined in evict.c */
/* This structure is used in order to represent the output buffer of a client,
* which is actually a linked list of blocks like that, that is: client->reply. */
typedef struct clientReplyBlock {
size_t size, used;
char buf[];