[HDFS-10412] Add optional non-thread support for better perfromance

• Type: Improvement
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Component/s: libhdfs
• Assignee: Unassigned
• Reporter: Stephen Bovy
• Created: 16/May/16 22:19
• Updated: 16/May/16 22:19

Description

I would like to propose some simple optional changes that would be activated by a compiler flag. These changes would enable a typical monolithic single threaded application to use libhdfs without the need to incur additional overhead for threads that is not needed.

Here is a proposed for these changes:

#1 add a new function to "jni_helper.c"

/** getSoloJNIEnv: A helper function to get the JNIEnv* for non-threaded use.

• If no JVM exists, then one will be created. JVM command line arguments
• are obtained from the LIBHDFS_OPTS environment variable.
• @param: None.
• @return The JNIEnv* for non-thread use.
• */
  JNIEnv* getSoloJNIEnv(void)
  {
  JNIEnv *env;
  env = getGlobalJNIEnv();
  if (!env) { fprintf(stderr, "getJNIEnv: getGlobalJNIEnv failed\n"); return NULL; }

  return env;
  }

Add the following the following to "hdfs.c"

#1 a static global variable : "JNIEnv* hdfsJNIEnv;"
#2 a MACRO: "GETJNIENV();"

#ifdef NOTHREAD
static JNIEnv* hdfsJNIEnv = NULL;
#define GETJNIENV() \
if (hdfsJNIEnv == NULL)

{ \ hdfsJNIEnv = getSoloJNIEnv(); \ }

\
env = hdfsJNIEnv;
#else
#define GETJNIENV() env = getJNIEnv();
#endif

The above NEW MACRO would be used as in the following example:

int hdfsFileGetReadStatistics(hdfsFile file,
struct hdfsReadStatistics **stats)

{ jthrowable jthr; jobject readStats = NULL; jvalue jVal; struct hdfsReadStatistics *s = NULL; int ret; JNIEnv* env; // JNIEnv* env = getJNIEnv(); GETJNIENV(); ( ... ) }