Lock the socket_mutex inside Socket_getReadySocket()

To reduce the performance penalty of commit 779ca42a
Ian has recommended to release the socket_mutex during the call of select.
See https://github.com/eclipse/paho.mqtt.c/issues/385#issuecomment-372299490

As a preparation for this, the locking of the socket_mutex is moved inside
the Socket_getReadySocket() function.
Signed-off-by: Juergen Kosel <juergen.kosel@softing.com>

src/MQTTAsync.c

@@ -2967,10 +2967,8 @@ static MQTTPacket* MQTTAsync_cycle(int* sock, unsigned long timeout, int* rc)
 	if ((*sock = SSLSocket_getPendingRead()) == -1)
 	{
 #endif
-		Thread_lock_mutex(socket_mutex);
 		/* 0 from getReadySocket indicates no work to do, -1 == error, but can happen normally */
-		*sock = Socket_getReadySocket(0, &tp);
-		Thread_unlock_mutex(socket_mutex);
+		*sock = Socket_getReadySocket(0, &tp,socket_mutex);
 		if (!tostop && *sock == 0 && (tp.tv_sec > 0L || tp.tv_usec > 0L))
 			MQTTAsync_sleep(100L);
 #if defined(OPENSSL)

src/MQTTClient.c

@@ -1684,9 +1684,7 @@ static MQTTPacket* MQTTClient_cycle(int* sock, unsigned long timeout, int* rc)
 	{
 		/* 0 from getReadySocket indicates no work to do, -1 == error, but can happen normally */
 #endif
-		Thread_lock_mutex(socket_mutex);
-		*sock = Socket_getReadySocket(0, &tp);
-		Thread_unlock_mutex(socket_mutex);
+		*sock = Socket_getReadySocket(0, &tp, socket_mutex);
 #if defined(OPENSSL)
 	}
 #endif

src/Socket.c

@@ -228,7 +228,7 @@ int isReady(int socket, fd_set* read_set, fd_set* write_set)
  *  @param tp the timeout to be used for the select, unless overridden
  *  @return the socket next ready, or 0 if none is ready
  */
-int Socket_getReadySocket(int more_work, struct timeval *tp)
+int Socket_getReadySocket(int more_work, struct timeval *tp, mutex_type mutex)
 {
 	int rc = 0;
 	static struct timeval zero = {0L, 0L}; /* 0 seconds */
@@ -236,6 +236,7 @@ int Socket_getReadySocket(int more_work, struct timeval *tp)
 	struct timeval timeout = one;
 
 	FUNC_ENTRY;
+	Thread_lock_mutex(mutex);
 	if (s.clientsds->count == 0)
 		goto exit;
 
@@ -301,6 +302,7 @@ int Socket_getReadySocket(int more_work, struct timeval *tp)
 		ListNextElement(s.clientsds, &s.cur_clientsds);
 	}
 exit:
+	Thread_unlock_mutex(mutex);
 	FUNC_EXIT_RC(rc);
 	return rc;
 } /* end getReadySocket */

src/Socket.h

@@ -18,6 +18,7 @@
 #if !defined(SOCKET_H)
 #define SOCKET_H
 
+#include "Thread.h" /* Needed for mutex_type */
 #include <sys/types.h>
 
 #if defined(WIN32) || defined(WIN64)
@@ -124,7 +125,7 @@ typedef struct
 
 void Socket_outInitialize(void);
 void Socket_outTerminate(void);
-int Socket_getReadySocket(int more_work, struct timeval *tp);
+int Socket_getReadySocket(int more_work, struct timeval *tp,mutex_type mutex);
 int Socket_getch(int socket, char* c);
 char *Socket_getdata(int socket, size_t bytes, size_t* actual_len);
 int Socket_putdatas(int socket, char* buf0, size_t buf0len, int count, char** buffers, size_t* buflens, int* frees);