Add support for listen(2) backlog definition

In high RPS environments, the default listen backlog is not sufficient, so
giving users the power to configure it is the right approach, especially
since it requires only minor modifications to the code.

1 files changed, 10 insertions, 13 deletions

diff --git a/src/anet.c b/src/anet.c
index fc585c8d1..2851318e2 100644
--- a/src/anet.c
+++ b/src/anet.c
@@ -361,17 +361,14 @@ int anetWrite(int fd, char *buf, int count)
     return totlen;
 }
 
-static int anetListen(char *err, int s, struct sockaddr *sa, socklen_t len) {
+static int anetListen(char *err, int s, struct sockaddr *sa, socklen_t len, int backlog) {
     if (bind(s,sa,len) == -1) {
         anetSetError(err, "bind: %s", strerror(errno));
         close(s);
         return ANET_ERR;
     }
 
-    /* Use a backlog of 512 entries. We pass 511 to the listen() call because
-     * the kernel does: backlogsize = roundup_pow_of_two(backlogsize + 1);
-     * which will thus give us a backlog of 512 entries */
-    if (listen(s, 511) == -1) {
+    if (listen(s, backlog) == -1) {
         anetSetError(err, "listen: %s", strerror(errno));
         close(s);
         return ANET_ERR;
@@ -389,7 +386,7 @@ static int anetV6Only(char *err, int s) {
     return ANET_OK;
 }
 
-static int _anetTcpServer(char *err, int port, char *bindaddr, int af)
+static int _anetTcpServer(char *err, int port, char *bindaddr, int af, int backlog)
 {
     int s, rv;
     char _port[6];  /* strlen("65535") */
@@ -411,7 +408,7 @@ static int _anetTcpServer(char *err, int port, char *bindaddr, int af)
 
         if (af == AF_INET6 && anetV6Only(err,s) == ANET_ERR) goto error;
         if (anetSetReuseAddr(err,s) == ANET_ERR) goto error;
-        if (anetListen(err,s,p->ai_addr,p->ai_addrlen) == ANET_ERR) goto error;
+        if (anetListen(err,s,p->ai_addr,p->ai_addrlen,backlog) == ANET_ERR) goto error;
         goto end;
     }
     if (p == NULL) {
@@ -426,17 +423,17 @@ end:
     return s;
 }
 
-int anetTcpServer(char *err, int port, char *bindaddr)
+int anetTcpServer(char *err, int port, char *bindaddr, int backlog)
 {
-    return _anetTcpServer(err, port, bindaddr, AF_INET);
+    return _anetTcpServer(err, port, bindaddr, AF_INET, backlog);
 }
 
-int anetTcp6Server(char *err, int port, char *bindaddr)
+int anetTcp6Server(char *err, int port, char *bindaddr, int backlog)
 {
-    return _anetTcpServer(err, port, bindaddr, AF_INET6);
+    return _anetTcpServer(err, port, bindaddr, AF_INET6, backlog);
 }
 
-int anetUnixServer(char *err, char *path, mode_t perm)
+int anetUnixServer(char *err, char *path, mode_t perm, int backlog)
 {
     int s;
     struct sockaddr_un sa;
@@ -447,7 +444,7 @@ int anetUnixServer(char *err, char *path, mode_t perm)
     memset(&sa,0,sizeof(sa));
     sa.sun_family = AF_LOCAL;
     strncpy(sa.sun_path,path,sizeof(sa.sun_path)-1);
-    if (anetListen(err,s,(struct sockaddr*)&sa,sizeof(sa)) == ANET_ERR)
+    if (anetListen(err,s,(struct sockaddr*)&sa,sizeof(sa),backlog) == ANET_ERR)
         return ANET_ERR;
     if (perm)
         chmod(sa.sun_path, perm);