common: Adding Select class

The Select class implements ::select (2) API with multiple tables or
file-descriptor.

Usage:
  Select cs;
  cs.addSelectable(&netlink);
  cs.addSelectable(&consumerTable);

  while (true)
  {
    Selectable *object;
    int tempfd;
    if (s.select(&object, &tempfd) != Select::OBJECT)
      break;

    // Check if object is consumerTable or netlink
  }

Signed-off-by: Elad Raz <[email protected]>

common/Makefile.am

@@ -14,7 +14,8 @@ libswsscommon_la_SOURCES = \
 	dbconnector.cpp           \
 	table.cpp                 \
 	json.cpp                  \
-	producertable.cpp
+	producertable.cpp         \
+	select.cpp
 
 libswsscommon_la_CFLAGS = $(DBGFLAGS) $(AM_CFLAGS) $(CFLAGS_COMMON)
 libswsscommon_la_CPPFLAGS = $(DBGFLAGS) $(AM_CFLAGS) $(CFLAGS_COMMON)

common/select.cpp

@@ -0,0 +1,81 @@
+#include "common/selectable.h"
+#include "common/select.h"
+#include <stdio.h>
+#include <sys/time.h>
+#include <sys/types.h>
+
+using namespace std;
+
+namespace swss {
+
+void Select::addSelectable(Selectable *c)
+{
+    m_objects.push_back(c);
+}
+
+void Select::addFd(int fd)
+{
+    m_fds.push_back(fd);
+}
+
+int Select::select(Selectable **c, int *fd, unsigned int timeout)
+{
+    struct timeval t = {0, (suseconds_t)(timeout)*1000};
+    struct timeval *pTimeout = NULL;
+    fd_set fs;
+    int err;
+
+    FD_ZERO(&fs);
+    *c = NULL;
+    *fd = 0;
+    if (timeout != std::numeric_limits<unsigned int>::max())
+        pTimeout = &t;
+
+    /* Checking caching from reader */
+    for (Selectable *i : m_objects)
+    {
+        err = i->readCache();
+        if (err == Selectable::ERROR)
+            return Select::ERROR;
+        else if (err == Selectable::DATA) {
+            *c = i;
+            return Select::OBJECT;
+        }
+        /* else, timeout = no data */
+
+        i->addFd(&fs);
+    }
+
+    for (int fd : m_fds)
+    {
+        FD_SET(fd, &fs);
+    }
+
+    err = ::select(FD_SETSIZE, &fs, NULL, NULL, pTimeout);
+    if (err < 0)
+        return Select::ERROR;
+    if (err == 0)
+        return Select::TIMEOUT;
+
+    /* Check other consumer-table */
+    for (Selectable *i : m_objects)
+        if (i->isMe(&fs))
+        {
+            i->readMe();
+            *c = i;
+            return Select::OBJECT;
+        }
+
+    /* Check other FDs */
+    for (int f : m_fds)
+        if (FD_ISSET(f, &fs))
+        {
+            *fd = f;
+            return Select::FD;
+        }
+
+    /* Shouldn't reach here */
+    return Select::ERROR;
+}
+
+};

common/select.h

@@ -0,0 +1,44 @@
+#ifndef __CONSUMERSELECT__
+#define __CONSUMERSELECT__
+
+#include <string>
+#include <vector>
+#include <limits>
+#include <hiredis/hiredis.h>
+#include "common/selectable.h"
+
+namespace swss {
+
+class Select
+{
+public:
+    /* Add object for select */
+    void addSelectable(Selectable *c);
+
+    /* Add file-descriptor for select  */
+    void addFd(int fd);
+
+    /*
+     * Wait until data will arrived, returns the object on which select()
+     * was signaled.
+     */
+    enum {
+        OBJECT = 0,
+        FD = 1,
+        ERROR = 2,
+        TIMEOUT = 3
+    };
+    int select(Selectable **c, int *fd,
+               unsigned int timeout = std::numeric_limits<unsigned int>::max());
+
+private:
+    /* Create a new redisContext, SELECT DB and SUBSRIBE */
+    void subsribe();
+
+    std::vector<Selectable * > m_objects;
+    std::vector<int> m_fds;
+};
+
+}
+
+#endif