/*
 * %W% %E%
 * 
 * Copyright (c) 2006, Oracle and/or its affiliates. All rights reserved.
 * 
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 * 
 * -Redistribution of source code must retain the above copyright notice, this
 *  list of conditions and the following disclaimer.
 * 
 * -Redistribution in binary form must reproduce the above copyright notice, 
 *  this list of conditions and the following disclaimer in the documentation
 *  and/or other materials provided with the distribution.
 * 
 * Neither the name of Oracle or the names of contributors may 
 * be used to endorse or promote products derived from this software without 
 * specific prior written permission.
 * 
 * This software is provided "AS IS," without a warranty of any kind. ALL 
 * EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND WARRANTIES, INCLUDING
 * ANY IMPLIED WARRANTY OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE
 * OR NON-INFRINGEMENT, ARE HEREBY EXCLUDED. SUN MICROSYSTEMS, INC. ("SUN")
 * AND ITS LICENSORS SHALL NOT BE LIABLE FOR ANY DAMAGES SUFFERED BY LICENSEE
 * AS A RESULT OF USING, MODIFYING OR DISTRIBUTING THIS SOFTWARE OR ITS
 * DERIVATIVES. IN NO EVENT WILL SUN OR ITS LICENSORS BE LIABLE FOR ANY LOST 
 * REVENUE, PROFIT OR DATA, OR FOR DIRECT, INDIRECT, SPECIAL, CONSEQUENTIAL, 
 * INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER CAUSED AND REGARDLESS OF THE THEORY 
 * OF LIABILITY, ARISING OUT OF THE USE OF OR INABILITY TO USE THIS SOFTWARE, 
 * EVEN IF SUN HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
 * 
 * You acknowledge that this software is not designed, licensed or intended
 * for use in the design, construction, operation or maintenance of any
 * nuclear facility.
 */

#include "stdlib.h"

#include "mtrace.h"
#include "java_crw_demo.h"
	    
	   
/* ------------------------------------------------------------------- */
/* Some constant maximum sizes */

#define MAX_TOKEN_LENGTH	16
#define MAX_THREAD_NAME_LENGTH 	512
#define MAX_METHOD_NAME_LENGTH  1024

/* Some constant names that tie to Java class/method names.
 *    We assume the Java class whose static methods we will be calling
 *    looks like:
 *
 * public class Mtrace {
 *     private static int engaged; 
 *     private static native void _method_entry(Object thr, int cnum, int mnum);
 *     public static void method_entry(int cnum, int mnum)
 *     {
 *   	   if ( engaged != 0 ) {
 *	       _method_entry(Thread.currentThread(), cnum, mnum);
 *	   }
 *     }
 *     private static native void _method_exit(Object thr, int cnum, int mnum);
 *     public static void method_exit(int cnum, int mnum)
 *     {
 * 	   if ( engaged != 0 ) {
 *	       _method_exit(Thread.currentThread(), cnum, mnum);
 *	   }
 *     }
 * }
 *
 *    The engaged field allows us to inject all classes (even system classes)
 *    and delay the actual calls to the native code until the VM has reached
 *    a safe time to call native methods (Past the JVMTI VM_START event).
 * 
 */

#define MTRACE_class	    Mtrace	    /* Name of class we are using */
#define MTRACE_entry        method_entry    /* Name of java entry method */
#define MTRACE_exit         method_exit     /* Name of java exit method */
#define MTRACE_native_entry _method_entry   /* Name of java entry native */
#define MTRACE_native_exit  _method_exit    /* Name of java exit native */
#define MTRACE_engaged      engaged         /* Name of java static field */

/* C macros to create strings from tokens */
#define _STRING(s) #s
#define STRING(s) _STRING(s)

/* ------------------------------------------------------------------- */

/* Data structure to hold method and class information in agent */

typedef struct MethodInfo {
    const char *name;          /* Method name */
    const char *signature;     /* Method signature */
    int         calls;         /* Method call count */
    int         returns;       /* Method return count */
} MethodInfo;

typedef struct ClassInfo {
    const char *name;          /* Class name */
    int         mcount;        /* Method count */
    MethodInfo *methods;       /* Method information */
    int         calls;         /* Method call count for this class */
} ClassInfo;

/* Global agent data structure */

typedef struct {
    /* JVMTI Environment */
    jvmtiEnv      *jvmti;
    jboolean       vm_is_dead;
    jboolean       vm_is_started;
    /* Data access Lock */
    jrawMonitorID  lock;
    /* Options */
    char           *include;
    char           *exclude;
    int             max_count;
    /* ClassInfo Table */
    ClassInfo      *classes;
    jint            ccount;
} GlobalAgentData;

static GlobalAgentData *gdata;

/* Enter a critical section by doing a JVMTI Raw Monitor Enter */
static void
enter_critical_section(jvmtiEnv *jvmti)
{
    jvmtiError error;
    
    error = (*jvmti)->RawMonitorEnter(jvmti, gdata->lock);
    check_jvmti_error(jvmti, error, "Cannot enter with raw monitor");
}

/* Exit a critical section by doing a JVMTI Raw Monitor Exit */
static void
exit_critical_section(jvmtiEnv *jvmti)
{
    jvmtiError error;
    
    error = (*jvmti)->RawMonitorExit(jvmti, gdata->lock);
    check_jvmti_error(jvmti, error, "Cannot exit with raw monitor");
}

/* Get a name for a jthread */
static void
get_thread_name(jvmtiEnv *jvmti, jthread thread, char *tname, int maxlen)
{
    jvmtiThreadInfo info;
    jvmtiError      error;

    /* Make sure the stack variables are garbage free */
    (void)memset(&info,0, sizeof(info));
    
    /* Assume the name is unknown for now */
    (void)strcpy(tname, "Unknown");
   
    /* Get the thread information, which includes the name */
    error = (*jvmti)->GetThreadInfo(jvmti, thread, &info);
    check_jvmti_error(jvmti, error, "Cannot get thread info");
  
    /* The thread might not have a name, be careful here. */
    if ( info.name != NULL ) {
	int len;

	/* Copy the thread name into tname if it will fit */
	len = (int)strlen(info.name);
	if ( len < maxlen ) {
	    (void)strcpy(tname, info.name);
	}
	
	/* Every string allocated by JVMTI needs to be freed */
	deallocate(jvmti, (void*)info.name);
    }
}

/* Qsort class compare routine */
static int
class_compar(const void *e1, const void *e2)
{
    ClassInfo *c1 = (ClassInfo*)e1;
    ClassInfo *c2 = (ClassInfo*)e2;
    if ( c1->calls > c2->calls ) return  1;
    if ( c1->calls < c2->calls ) return -1;
    return 0;
}

/* Qsort method compare routine */
static int
method_compar(const void *e1, const void *e2)
{
    MethodInfo *m1 = (MethodInfo*)e1;
    MethodInfo *m2 = (MethodInfo*)e2;
    if ( m1->calls > m2->calls ) return  1;
    if ( m1->calls < m2->calls ) return -1;
    return 0;
}

/* Callback from java_crw_demo() that gives us mnum mappings */
static void
mnum_callbacks(unsigned cnum, const char **names, const char**sigs, int mcount)
{
    ClassInfo  *cp;
    int         mnum;

    if ( cnum >= (unsigned)gdata->ccount ) {
	fatal_error("ERROR: Class number out of range\n");
    }
    if ( mcount == 0 ) {
	return;
    }
    
    cp           = gdata->classes + (int)cnum;
    cp->calls    = 0;
    cp->mcount   = mcount;
    cp->methods  = (MethodInfo*)calloc(mcount, sizeof(MethodInfo));
    if ( cp->methods == NULL ) {
	fatal_error("ERROR: Out of malloc memory\n");
    }
    
    for ( mnum = 0 ; mnum < mcount ; mnum++ ) {
        MethodInfo *mp;

	mp            = cp->methods + mnum;
        mp->name      = (const char *)strdup(names[mnum]);
	if ( mp->name == NULL ) {
	    fatal_error("ERROR: Out of malloc memory\n");
	}
        mp->signature = (const char *)strdup(sigs[mnum]);
	if ( mp->signature == NULL ) {
	    fatal_error("ERROR: Out of malloc memory\n");
	}
    }
}

/* Java Native Method for entry */
static void
MTRACE_native_entry(JNIEnv *env, jclass klass, jobject thread, jint cnum, jint mnum)
{
    enter_critical_section(gdata->jvmti); {
	/* It's possible we get here right after VmDeath event, be careful */
	if ( !gdata->vm_is_dead ) {
            ClassInfo  *cp;
            MethodInfo *mp;
	    
	    if ( cnum >= gdata->ccount ) {
		fatal_error("ERROR: Class number out of range\n");
	    }
            cp = gdata->classes + cnum;
	    if ( mnum >= cp->mcount ) {
		fatal_error("ERROR: Method number out of range\n");
	    }
	    mp = cp->methods + mnum;
            if ( interested((char*)cp->name, (char*)mp->name, 
	                    gdata->include, gdata->exclude)  ) {
		mp->calls++;
		cp->calls++;
	    }
	}
    } exit_critical_section(gdata->jvmti);
}

/* Java Native Method for exit */
static void
MTRACE_native_exit(JNIEnv *env, jclass klass, jobject thread, jint cnum, jint mnum)
{
    enter_critical_section(gdata->jvmti); {
	/* It's possible we get here right after VmDeath event, be careful */
	if ( !gdata->vm_is_dead ) {
            ClassInfo  *cp;
            MethodInfo *mp;
	    
	    if ( cnum >= gdata->ccount ) {
		fatal_error("ERROR: Class number out of range\n");
	    }
            cp = gdata->classes + cnum;
	    if ( mnum >= cp->mcount ) {
		fatal_error("ERROR: Method number out of range\n");
	    }
	    mp = cp->methods + mnum;
            if ( interested((char*)cp->name, (char*)mp->name, 
	                    gdata->include, gdata->exclude)  ) {
		mp->returns++;
	    }
	}
    } exit_critical_section(gdata->jvmti);
}

/* Callback for JVMTI_EVENT_VM_START */
static void JNICALL
cbVMStart(jvmtiEnv *jvmti, JNIEnv *env)
{
    enter_critical_section(jvmti); {
        jclass   klass;
	jfieldID field;
	int      rc;

	/* Java Native Methods for class */
	static JNINativeMethod registry[2] = {
	    {STRING(MTRACE_native_entry), "(Ljava/lang/Object;II)V", 
		(void*)&MTRACE_native_entry},
	    {STRING(MTRACE_native_exit),  "(Ljava/lang/Object;II)V", 
		(void*)&MTRACE_native_exit}
        };
	
	/* The VM has started. */
	stdout_message("VMStart\n");

	/* Register Natives for class whose methods we use */
	klass = (*env)->FindClass(env, STRING(MTRACE_class));
	if ( klass == NULL ) {
	    fatal_error("ERROR: JNI: Cannot find %s with FindClass\n", 
			STRING(MTRACE_class));
	}
	rc = (*env)->RegisterNatives(env, klass, registry, 2);
	if ( rc != 0 ) {
	    fatal_error("ERROR: JNI: Cannot register native methods for %s\n", 
			STRING(MTRACE_class));
	}
	
	/* Engage calls. */
	field = (*env)->GetStaticFieldID(env, klass, STRING(MTRACE_engaged), "I");
	if ( field == NULL ) {
	    fatal_error("ERROR: JNI: Cannot get field from %s\n", 
			STRING(MTRACE_class));
	}
	(*env)->SetStaticIntField(env, klass, field, 1);

        /* Indicate VM has started */
        gdata->vm_is_started = JNI_TRUE;
    
    } exit_critical_section(jvmti);
}

/* Callback for JVMTI_EVENT_VM_INIT */
static void JNICALL
cbVMInit(jvmtiEnv *jvmti, JNIEnv *env, jthread thread)
{
    enter_critical_section(jvmti); {
	char  tname[MAX_THREAD_NAME_LENGTH];
	static jvmtiEvent events[] = 
		{ JVMTI_EVENT_THREAD_START, JVMTI_EVENT_THREAD_END };
	int        i;

	/* The VM has started. */
	get_thread_name(jvmti, thread, tname, sizeof(tname));
	stdout_message("VMInit %s\n", tname);

	/* The VM is now initialized, at this time we make our requests
	 *   for additional events.
	 */

	for( i=0; i < (int)(sizeof(events)/sizeof(jvmtiEvent)); i++) {
	    jvmtiError error;

	    /* Setup event  notification modes */
	    error = (*jvmti)->SetEventNotificationMode(jvmti, JVMTI_ENABLE, 
				  events[i], (jthread)NULL);
	    check_jvmti_error(jvmti, error, "Cannot set event notification");
	}

    } exit_critical_section(jvmti);
}

/* Callback for JVMTI_EVENT_VM_DEATH */
static void JNICALL
cbVMDeath(jvmtiEnv *jvmti, JNIEnv *env)
{
    enter_critical_section(jvmti); {
        jclass   klass;
	jfieldID field;

	/* The VM has died. */
	stdout_message("VMDeath\n");

	/* Disengage calls in MTRACE_class. */
	klass = (*env)->FindClass(env, STRING(MTRACE_class));
	if ( klass == NULL ) {
	    fatal_error("ERROR: JNI: Cannot find %s with FindClass\n", 
			STRING(MTRACE_class));
	}
	field = (*env)->GetStaticFieldID(env, klass, STRING(MTRACE_engaged), "I");
	if ( field == NULL ) {
	    fatal_error("ERROR: JNI: Cannot get field from %s\n", 
			STRING(MTRACE_class));
	}
	(*env)->SetStaticIntField(env, klass, field, 0);

	/* The critical section here is important to hold back the VM death
	 *    until all other callbacks have completed.
	 */

	/* Since this critical section could be holding up other threads
	 *   in other event callbacks, we need to indicate that the VM is
	 *   dead so that the other callbacks can short circuit their work.
	 *   We don't expect any further events after VmDeath but we do need
	 *   to be careful that existing threads might be in our own agent
	 *   callback code.
	 */
	gdata->vm_is_dead = JNI_TRUE;

	/* Dump out stats */
	stdout_message("Begin Class Stats\n");
	if ( gdata->ccount > 0 ) {
	    int cnum;
	    
	    /* Sort table (in place) by number of method calls into class. */
	    /*  Note: Do not use this table after this qsort! */
	    qsort(gdata->classes, gdata->ccount, sizeof(ClassInfo),
			&class_compar);
	    
	    /* Dump out gdata->max_count most called classes */
	    for ( cnum=gdata->ccount-1 ; 
		  cnum >= 0 && cnum >= gdata->ccount - gdata->max_count; 
		  cnum-- ) {
		ClassInfo *cp;
	        int        mnum;
		
		cp = gdata->classes + cnum;
		stdout_message("Class %s %d calls\n", cp->name, cp->calls);
		if ( cp->calls==0 ) continue;
		
		/* Sort method table (in place) by number of method calls. */
		/*  Note: Do not use this table after this qsort! */
		qsort(cp->methods, cp->mcount, sizeof(MethodInfo),
			    &method_compar);
		for ( mnum=cp->mcount-1 ; mnum >= 0 ; mnum-- ) {
		    MethodInfo *mp;

		    mp = cp->methods + mnum;
		    if ( mp->calls==0 ) continue;
		    stdout_message("\tMethod %s %s %d calls %d returns\n",
			mp->name, mp->signature, mp->calls, mp->returns);
		}
	    }
	}
	stdout_message("End Class Stats\n");
	(void)fflush(stdout);
    
    } exit_critical_section(jvmti);
	
}  

/* Callback for JVMTI_EVENT_THREAD_START */
static void JNICALL
cbThreadStart(jvmtiEnv *jvmti, JNIEnv *env, jthread thread)
{
    enter_critical_section(jvmti); {
	/* It's possible we get here right after VmDeath event, be careful */
	if ( !gdata->vm_is_dead ) {
	    char  tname[MAX_THREAD_NAME_LENGTH];
	    
	    get_thread_name(jvmti, thread, tname, sizeof(tname));
	    stdout_message("ThreadStart %s\n", tname);
	}
    } exit_critical_section(jvmti);
}

/* Callback for JVMTI_EVENT_THREAD_END */
static void JNICALL
cbThreadEnd(jvmtiEnv *jvmti, JNIEnv *env, jthread thread)
{
    enter_critical_section(jvmti); {
	/* It's possible we get here right after VmDeath event, be careful */
	if ( !gdata->vm_is_dead ) {
	    char  tname[MAX_THREAD_NAME_LENGTH];
	    
	    get_thread_name(jvmti, thread, tname, sizeof(tname));
	    stdout_message("ThreadEnd %s\n", tname);
	}
    } exit_critical_section(jvmti);
}

/* Callback for JVMTI_EVENT_CLASS_FILE_LOAD_HOOK */
static void JNICALL
cbClassFileLoadHook(jvmtiEnv *jvmti, JNIEnv* env,
                jclass class_being_redefined, jobject loader,
                const char* name, jobject protection_domain,
                jint class_data_len, const unsigned char* class_data,
                jint* new_class_data_len, unsigned char** new_class_data)
{
    enter_critical_section(jvmti); {
	/* It's possible we get here right after VmDeath event, be careful */
	if ( !gdata->vm_is_dead ) {

	    const char *classname;

            /* Name could be NULL */
	    if ( name == NULL ) {
		classname = java_crw_demo_classname(class_data, class_data_len,
			NULL);
		if ( classname == NULL ) {
		    fatal_error("ERROR: No classname inside classfile\n");
		}
	    } else {
		classname = strdup(name);
		if ( classname == NULL ) {
		    fatal_error("ERROR: Out of malloc memory\n");
		}
	    }
	    
	    *new_class_data_len = 0;
            *new_class_data     = NULL;

            /* The tracker class itself? */
            if ( interested((char*)classname, "", gdata->include, gdata->exclude) 
		  &&  strcmp(classname, STRING(MTRACE_class)) != 0 ) {
                jint           cnum;
                int            system_class;
                unsigned char *new_image;
                long           new_length;
		ClassInfo     *cp;

                /* Get unique number for every class file image loaded */
                cnum = gdata->ccount++;

		/* Save away class information */
		if ( gdata->classes == NULL ) {
		    gdata->classes = (ClassInfo*)malloc(
				gdata->ccount*sizeof(ClassInfo));
                } else {
		    gdata->classes = (ClassInfo*)
				realloc((void*)gdata->classes,
				gdata->ccount*sizeof(ClassInfo));
		}
		if ( gdata->classes == NULL ) {
		    fatal_error("ERROR: Out of malloc memory\n");
		}
		cp           = gdata->classes + cnum;
		cp->name     = (const char *)strdup(classname);
		if ( cp->name == NULL ) {
		    fatal_error("ERROR: Out of malloc memory\n");
		}
		cp->calls    = 0;
		cp->mcount   = 0;
		cp->methods  = NULL;

                /* Is it a system class? If the class load is before VmStart
		 *   then we will consider it a system class that should
		 *   be treated carefully. (See java_crw_demo)
		 */
                system_class = 0;
                if ( !gdata->vm_is_started ) {
                    system_class = 1;
                }

                new_image = NULL;
                new_length = 0;

                /* Call the class file reader/write demo code */
                java_crw_demo(cnum,
                    classname,
                    class_data,
                    class_data_len,
                    system_class,
                    STRING(MTRACE_class), "L" STRING(MTRACE_class) ";",
                    STRING(MTRACE_entry), "(II)V",
                    STRING(MTRACE_exit), "(II)V",
                    NULL, NULL,
                    NULL, NULL,
                    &new_image,
                    &new_length,
                    NULL,
                    &mnum_callbacks);

		/* If we got back a new class image, return it back as "the"
		 *   new class image. This must be JVMTI Allocate space.
		 */
                if ( new_length > 0 ) {
                    unsigned char *jvmti_space;

                    jvmti_space = (unsigned char *)allocate(jvmti, (jint)new_length);
                    (void)memcpy((void*)jvmti_space, (void*)new_image, (int)new_length);
                    *new_class_data_len = (jint)new_length;
                    *new_class_data     = jvmti_space; /* VM will deallocate */
                }

		/* Always free up the space we get from java_crw_demo() */
                if ( new_image != NULL ) {
                    (void)free((void*)new_image); /* Free malloc() space with free() */
                }
            }
	    (void)free((void*)classname);
	}
    } exit_critical_section(jvmti);
}

/* Parse the options for this mtrace agent */
static void
parse_agent_options(char *options)
{
    char token[MAX_TOKEN_LENGTH];
    char *next;

    gdata->max_count = 10; /* Default max=n */
    
    /* Parse options and set flags in gdata */
    if ( options==NULL ) {
	return;
    }
   
    /* Get the first token from the options string. */
    next = get_token(options, ",=", token, sizeof(token));

    /* While not at the end of the options string, process this option. */
    while ( next != NULL ) {
	if ( strcmp(token,"help")==0 ) {
	    stdout_message("The mtrace JVMTI demo agent\n");
	    stdout_message("\n");
	    stdout_message(" java -agent:mtrace[=options] ...\n");
	    stdout_message("\n");
	    stdout_message("The options are comma separated:\n");
	    stdout_message("\t help\t\t\t Print help information\n");
	    stdout_message("\t max=n\t\t Only list top n classes\n");
	    stdout_message("\t include=item\t\t Only these classes/methods\n");
	    stdout_message("\t exclude=item\t\t Exclude these classes/methods\n");
	    stdout_message("\n");
	    stdout_message("item\t Qualified class and/or method names\n");
	    stdout_message("\t\t e.g. (*.<init>;Foobar.method;sun.*)\n");
	    stdout_message("\n");
	    exit(0);
	} else if ( strcmp(token,"max")==0 ) {
            char number[MAX_TOKEN_LENGTH];
	    
	    /* Get the numeric option */
	    next = get_token(next, ",=", number, (int)sizeof(number));
	    /* Check for token scan error */
	    if ( next==NULL ) {
		fatal_error("ERROR: max=n option error\n");
	    }
	    /* Save numeric value */
	    gdata->max_count = atoi(number);
	} else if ( strcmp(token,"include")==0 ) {
	    int   used;
	    int   maxlen;

	    maxlen = MAX_METHOD_NAME_LENGTH;
	    if ( gdata->include == NULL ) {
		gdata->include = (char*)calloc(maxlen+1, 1);
		used = 0;
	    } else {
		used  = (int)strlen(gdata->include);
		gdata->include[used++] = ',';
		gdata->include[used] = 0;
		gdata->include = (char*)
			     realloc((void*)gdata->include, used+maxlen+1);
	    }
	    if ( gdata->include == NULL ) {
		fatal_error("ERROR: Out of malloc memory\n");
	    }
	    /* Add this item to the list */
	    next = get_token(next, ",=", gdata->include+used, maxlen);
	    /* Check for token scan error */
	    if ( next==NULL ) {
		fatal_error("ERROR: include option error\n");
	    }
	} else if ( strcmp(token,"exclude")==0 ) {
	    int   used;
	    int   maxlen;

	    maxlen = MAX_METHOD_NAME_LENGTH;
	    if ( gdata->exclude == NULL ) {
		gdata->exclude = (char*)calloc(maxlen+1, 1);
		used = 0;
	    } else {
		used  = (int)strlen(gdata->exclude);
		gdata->exclude[used++] = ',';
		gdata->exclude[used] = 0;
		gdata->exclude = (char*)
			     realloc((void*)gdata->exclude, used+maxlen+1);
	    }
	    if ( gdata->exclude == NULL ) {
		fatal_error("ERROR: Out of malloc memory\n");
	    }
	    /* Add this item to the list */
	    next = get_token(next, ",=", gdata->exclude+used, maxlen);
	    /* Check for token scan error */
	    if ( next==NULL ) {
		fatal_error("ERROR: exclude option error\n");
	    }
	} else if ( token[0]!=0 ) {
	    /* We got a non-empty token and we don't know what it is. */
	    fatal_error("ERROR: Unknown option: %s\n", token);
	}
	/* Get the next token (returns NULL if there are no more) */
        next = get_token(next, ",=", token, sizeof(token));
    }
}

/* Agent_OnLoad: This is called immediately after the shared library is 
 *   loaded. This is the first code executed.
 */
JNIEXPORT jint JNICALL 
Agent_OnLoad(JavaVM *vm, char *options, void *reserved)
{
    static GlobalAgentData data;
    jvmtiEnv              *jvmti;
    jvmtiError             error;
    jint                   res;
    jvmtiCapabilities      capabilities;
    jvmtiEventCallbacks    callbacks;
    
    /* Setup initial global agent data area 
     *   Use of static/extern data should be handled carefully here.
     *   We need to make sure that we are able to cleanup after ourselves
     *     so anything allocated in this library needs to be freed in
     *     the Agent_OnUnload() function.
     */
    (void)memset((void*)&data, 0, sizeof(data));
    gdata = &data;
   
    /* First thing we need to do is get the jvmtiEnv* or JVMTI environment */
    res = (*vm)->GetEnv(vm, (void **)&jvmti, JVMTI_VERSION_1);
    if (res != JNI_OK) {
	/* This means that the VM was unable to obtain this version of the
	 *   JVMTI interface, this is a fatal error.
	 */
	fatal_error("ERROR: Unable to access JVMTI Version 1 (0x%x),"
                " is your JDK a 5.0 or newer version?"
                " JNIEnv's GetEnv() returned %d\n",
               JVMTI_VERSION_1, res);
    }

    /* Here we save the jvmtiEnv* for Agent_OnUnload(). */
    gdata->jvmti = jvmti;
   
    /* Parse any options supplied on java command line */
    parse_agent_options(options);
   
    /* Immediately after getting the jvmtiEnv* we need to ask for the
     *   capabilities this agent will need. In this case we need to make
     *   sure that we can get all class load hooks.
     */
    (void)memset(&capabilities,0, sizeof(capabilities));
    capabilities.can_generate_all_class_hook_events  = 1;
    error = (*jvmti)->AddCapabilities(jvmti, &capabilities);
    check_jvmti_error(jvmti, error, "Unable to get necessary JVMTI capabilities.");
    
    /* Next we need to provide the pointers to the callback functions to
     *   to this jvmtiEnv*
     */
    (void)memset(&callbacks,0, sizeof(callbacks));
    /* JVMTI_EVENT_VM_START */
    callbacks.VMStart           = &cbVMStart;      
    /* JVMTI_EVENT_VM_INIT */
    callbacks.VMInit            = &cbVMInit;      
    /* JVMTI_EVENT_VM_DEATH */
    callbacks.VMDeath           = &cbVMDeath;     
    /* JVMTI_EVENT_CLASS_FILE_LOAD_HOOK */
    callbacks.ClassFileLoadHook = &cbClassFileLoadHook; 
    /* JVMTI_EVENT_THREAD_START */
    callbacks.ThreadStart       = &cbThreadStart; 
    /* JVMTI_EVENT_THREAD_END */
    callbacks.ThreadEnd         = &cbThreadEnd;   
    error = (*jvmti)->SetEventCallbacks(jvmti, &callbacks, (jint)sizeof(callbacks));
    check_jvmti_error(jvmti, error, "Cannot set jvmti callbacks");
   
    /* At first the only initial events we are interested in are VM
     *   initialization, VM death, and Class File Loads. 
     *   Once the VM is initialized we will request more events.
     */
    error = (*jvmti)->SetEventNotificationMode(jvmti, JVMTI_ENABLE, 
			  JVMTI_EVENT_VM_START, (jthread)NULL);
    check_jvmti_error(jvmti, error, "Cannot set event notification");
    error = (*jvmti)->SetEventNotificationMode(jvmti, JVMTI_ENABLE, 
			  JVMTI_EVENT_VM_INIT, (jthread)NULL);
    check_jvmti_error(jvmti, error, "Cannot set event notification");
    error = (*jvmti)->SetEventNotificationMode(jvmti, JVMTI_ENABLE, 
			  JVMTI_EVENT_VM_DEATH, (jthread)NULL);
    check_jvmti_error(jvmti, error, "Cannot set event notification");
    error = (*jvmti)->SetEventNotificationMode(jvmti, JVMTI_ENABLE, 
			  JVMTI_EVENT_CLASS_FILE_LOAD_HOOK, (jthread)NULL);
    check_jvmti_error(jvmti, error, "Cannot set event notification");
   
    /* Here we create a raw monitor for our use in this agent to
     *   protect critical sections of code.
     */
    error = (*jvmti)->CreateRawMonitor(jvmti, "agent data", &(gdata->lock));
    check_jvmti_error(jvmti, error, "Cannot create raw monitor");

    /* Add demo jar file to boot classpath */
    add_demo_jar_to_bootclasspath(jvmti, "mtrace");

    /* We return JNI_OK to signify success */
    return JNI_OK;
}

/* Agent_OnUnload: This is called immediately before the shared library is 
 *   unloaded. This is the last code executed.
 */
JNIEXPORT void JNICALL 
Agent_OnUnload(JavaVM *vm)
{
    /* Make sure all malloc/calloc/strdup space is freed */
    if ( gdata->include != NULL ) {
	(void)free((void*)gdata->include);
	gdata->include = NULL;
    }
    if ( gdata->exclude != NULL ) {
	(void)free((void*)gdata->exclude);
	gdata->exclude = NULL;
    }
    if ( gdata->classes != NULL ) {
	int cnum;
	
	for ( cnum = 0 ; cnum < gdata->ccount ; cnum++ ) {
	    ClassInfo *cp;

	    cp = gdata->classes + cnum;
	    (void)free((void*)cp->name);
	    if ( cp->mcount > 0 ) {
	        int mnum;
		
		for ( mnum = 0 ; mnum < cp->mcount ; mnum++ ) {
		    MethodInfo *mp;

		    mp = cp->methods + mnum;
		    (void)free((void*)mp->name);
		    (void)free((void*)mp->signature);
		}
		(void)free((void*)cp->methods);
	    }
	}
	(void)free((void*)gdata->classes);
	gdata->classes = NULL;
    }
}

