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Date: Mon, 16 May 2016 22:20:12 +0000 (UTC)
From: "Stephen Bovy (JIRA)" <jira@apache.org>
To: hdfs-dev@hadoop.apache.org
Message-ID: <JIRA.12970177.1463437165000.202441.1463437212907@Atlassian.JIRA>
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Subject: [jira] [Created] (HDFS-10412) Add optional non-thread support for
 better perfromance
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archived-at: Mon, 16 May 2016 22:20:15 -0000

Stephen Bovy created HDFS-10412:
-----------------------------------

             Summary: Add optional non-thread support for better perfromance
                 Key: HDFS-10412
                 URL: https://issues.apache.org/jira/browse/HDFS-10412
             Project: Hadoop HDFS
          Issue Type: Improvement
          Components: libhdfs
            Reporter: Stephen Bovy
            Priority: Minor


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();

    ( ... )

}


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