Suggest some fine-tuning for foreign PR

In [PR_127] we got miscellaneous improvements. But we do no longer use
poll and therefore are back to the FD_SETSIZE limit of *select*.

This commit suggests some fine-tuning to [PR_127]. It does so by
replacing a possible SEGFAULT (aka crashing the whole JVM) by throwing a
java exception instead. This improves the reported error and even
enables user code to react to the situation.

Still not perfect. But IMHO good enough for now. We can still improve
later (for example as soon there's enough time to do so).

[PR_127]: java-native#127

src/main/cpp/_nix_based/jssc.cpp

@@ -40,19 +40,9 @@
 #endif
 #ifdef __APPLE__
     #include <serial/ioss.h>//Needed for IOSSIOSPEED in Mac OS X (Non standard baudrate)
-#elif !defined(HAVE_POLL)
-    // Seems as poll has some portability issues on OsX (Search for "poll" in
-    // "https://cr.yp.to/docs/unixport.html"). So we only make use of poll on
-    // all platforms except "__APPLE__".
-    // If you want to force usage of 'poll', pass "-DHAVE_POLL=1" to gcc.
-    #define HAVE_POLL 1
 #endif
 
-#if HAVE_POLL == 0
-    #include <sys/select.h>
-#else
-    #include <poll.h>
-#endif
+#include <sys/select.h>
 
 #include <jni.h>
 #include <jssc_SerialNativeInterface.h>
@@ -527,15 +517,23 @@ JNIEXPORT jboolean JNICALL Java_jssc_SerialNativeInterface_setDTR
  */
 JNIEXPORT jboolean JNICALL Java_jssc_SerialNativeInterface_writeBytes
   (JNIEnv *env, jobject, jlong portHandle, jbyteArray buffer){
-    jbyte* jBuffer = env->GetByteArrayElements(buffer, JNI_FALSE);
+    jbyte* jBuffer = NULL;
     jint bufferSize = env->GetArrayLength(buffer);
     fd_set write_fd_set;
     int byteRemains = bufferSize;
     struct timeval timeout;
     int result;
     jclass threadClass = env->FindClass("java/lang/Thread");
     jmethodID areWeInterruptedMethod = env->GetStaticMethodID(threadClass, "interrupted", "()Z");
-
+
+    if (portHandle < 0 || portHandle > FD_SETSIZE) {
+        char msg[95];
+        snprintf(msg, sizeof msg, "select(): file descriptor %ld outside expected range 0..%d", portHandle, FD_SETSIZE);
+        return env->ThrowNew(env->FindClass("java/lang/IndexOutOfBoundsException"), msg);
+    }
+
+    jBuffer = env->GetByteArrayElements(buffer, JNI_FALSE);
+
     while(byteRemains > 0) {
 
         // Check if the java thread has been interrupted, and if so, throw the exception
@@ -576,70 +574,29 @@ JNIEXPORT jboolean JNICALL Java_jssc_SerialNativeInterface_writeBytes
     return JNI_TRUE; //result == bufferSize ? JNI_TRUE : JNI_FALSE;
 }
 
-/**
- * Waits until 'read()' has something to tell for the specified filedescriptor.
- */
-/*
-static void awaitReadReady(JNIEnv*, jlong fd){
-#if HAVE_POLL == 0
-    // Alternative impl using 'select' as 'poll' isn't available (or broken).
-
-    //assert(fd < FD_SETSIZE); // <- Might help when hunting SEGFAULTs.
-    fd_set readFds;
-    while(true) {
-        FD_ZERO(&readFds);
-        FD_SET(fd, &readFds);
-        int result = select(fd + 1, &readFds, NULL, NULL, NULL);
-        if(result < 0){
-            // man select: On error, -1 is returned, and errno is set to indicate the error
-            // TODO: Maybe a candidate to raise a java exception. But won't do
-            //       yet for backward compatibility.
-            continue;
-        }
-        // Did wait successfully.
-        break;
-    }
-    FD_CLR(fd, &readFds);
-
-#else
-    // Default impl using 'poll'. This is more robust against fd>=1024 (eg
-    // SEGFAULT problems).
-
-    struct pollfd fds[1];
-    fds[0].fd = fd;
-    fds[0].events = POLLIN;
-    while(true){
-        int result = poll(fds, 1, -1);
-        if(result < 0){
-            // man poll: On error, -1 is returned, and errno is set to indicate the error.
-            // TODO: Maybe a candidate to raise a java exception. But won't do
-            //       yet for backward compatibility.
-            continue;
-        }
-        // Did wait successfully.
-        break;
-    }
 
-#endif
-}
-*/
-
-/* OK */
 /*
  * Reading data from the port
- *
- * Rewritten to use poll() instead of select() to handle fd>=1024
  */
 JNIEXPORT jbyteArray JNICALL Java_jssc_SerialNativeInterface_readBytes
   (JNIEnv *env, jobject, jlong portHandle, jint byteCount){
     fd_set read_fd_set;
-    jbyte *lpBuffer = new jbyte[byteCount];
+    jbyte *lpBuffer = NULL;
     int byteRemains = byteCount;
     struct timeval timeout;
     int result;
     jclass threadClass = env->FindClass("java/lang/Thread");
     jmethodID areWeInterruptedMethod = env->GetStaticMethodID(threadClass, "interrupted", "()Z");
-
+
+    if (portHandle < 0 || portHandle > FD_SETSIZE) {
+        char msg[95];
+        snprintf(msg, sizeof msg, "select(): file descriptor %ld outside expected range 0..%d", portHandle, FD_SETSIZE);
+        env->ThrowNew(env->FindClass("java/lang/IndexOutOfBoundsException"), msg);
+        return NULL;
+    }
+
+    lpBuffer = new jbyte[byteCount];
+
     while(byteRemains > 0) {
 
         // Check if the java thread has been interrupted, and if so, throw the exception