Path length limits on Windows leads to obscure class loading failures

As reported in the analysis of JDK-8187884

Calvin Cheung added a comment - 5 hours ago
I did more investigation by instrumenting the ClassPathDirEntry::open_stream() in classLoader.cpp
and found that when it failed, it is due to the jio_snprintf() failed and returning NULL.
  if (jio_snprintf(path, JVM_MAXPATHLEN, "%s%s%s", _dir, os::file_separator(), name) == -1) {
    FREE_RESOURCE_ARRAY(char, path, JVM_MAXPATHLEN);
    return NULL;
  }

Returning NULL in the above subsequently causes the systemDictionary.cpp throws a CNFE as indicated by David in the above comment.

jio_snprintf() fails due to the JVM_MAXPATHLEN is too short on windows.

In jvm_windows.h:

#define JVM_MAXPATHLEN _MAX_PATH

According to MSDN, MAX_PATH is defined as 260

https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247(v=vs.85).aspx

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We need to get rid of this small path limitation if possible and also improve the error diagnostics so that it is evident why we are failing to load the class!