Increate backlog of lldb-platform's listener socket

lldb-platform's listener socket only had a backlog of one connection.
That means that if more than one client connected simultaneously, the
connection would be refused. The test suite can be run remotely with
dozens of threads connecting simultaneously. Raised this limit to 100
to effectively eliminate lost connections.

Test Plan:
run tests against a remote target

Differential Revision: http://reviews.llvm.org/D8696

llvm-svn: 233652

lldb/include/lldb/Host/Socket.h

@@ -56,7 +56,12 @@ class Socket : public IOObject
     // Initialize a Tcp Socket object in listening mode.  listen and accept are implemented
     // separately because the caller may wish to manipulate or query the socket after it is
     // initialized, but before entering a blocking accept.
-    static Error TcpListen(llvm::StringRef host_and_port, bool child_processes_inherit, Socket *&socket, Predicate<uint16_t>* predicate);
+    static Error TcpListen(
+        llvm::StringRef host_and_port,
+        bool child_processes_inherit,
+        Socket *&socket,
+        Predicate<uint16_t>* predicate,
+        int backlog = 5);
     static Error TcpConnect(llvm::StringRef host_and_port, bool child_processes_inherit, Socket *&socket);
     static Error UdpConnect(llvm::StringRef host_and_port, bool child_processes_inherit, Socket *&send_socket, Socket *&recv_socket);
     static Error UnixDomainConnect(llvm::StringRef host_and_port, bool child_processes_inherit, Socket *&socket);

lldb/source/Host/common/Socket.cpp

@@ -167,7 +167,12 @@ Error Socket::TcpConnect(llvm::StringRef host_and_port, bool child_processes_inh
     return error;
 }
 
-Error Socket::TcpListen(llvm::StringRef host_and_port, bool child_processes_inherit, Socket *&socket, Predicate<uint16_t>* predicate)
+Error Socket::TcpListen(
+    llvm::StringRef host_and_port,
+    bool child_processes_inherit,
+    Socket *&socket,
+    Predicate<uint16_t>* predicate,
+    int backlog)
 {
     std::unique_ptr<Socket> listen_socket;
     NativeSocket listen_sock = kInvalidSocketValue;
@@ -209,7 +214,7 @@ Error Socket::TcpListen(llvm::StringRef host_and_port, bool child_processes_inhe
             return error;
         }
 
-        err = ::listen (listen_sock, 1);
+        err = ::listen (listen_sock, backlog);
         if (err == -1)
         {
             // TODO: On Windows, use WSAGetLastError()

lldb/tools/lldb-server/lldb-platform.cpp

@@ -253,7 +253,12 @@ main_platform (int argc, char *argv[])
     Socket *socket = nullptr;
     printf ("Listening for a connection from %s...\n", listen_host_port.c_str());
     const bool children_inherit_listen_socket = false;
-    error = Socket::TcpListen(listen_host_port.c_str(), children_inherit_listen_socket, socket, NULL);
+
+    // the test suite makes many connections in parallel, let's not miss any.
+    // The highest this should get reasonably is a function of the number 
+    // of target CPUs.  For now, let's just use 100
+    const int backlog = 100;
+    error = Socket::TcpListen(listen_host_port.c_str(), children_inherit_listen_socket, socket, NULL, backlog);
     if (error.Fail())
     {
         printf("error: %s\n", error.AsCString());