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Re:Race condition in Oracle C Interface?

From: <dgoulet_at_vicr.com>
Date: Mon, 20 Nov 2000 09:17:15 -0500
Message-Id: <10686.122489@fatcity.com> 





Michael,



    Sorry, but I'm not a OCI person.  I personally prefer Pro*C as it's much
easier to maintain & read.  To your point though, I've written many a Pro*C
program that does exactly what your trying without any difficulty and they all
behave very well.  Is there a reason why your using OCI?  I've found it to be a
very good way to shoot oneself in the foot regularly over the years.



Dick Goulet


____________________Reply Separator____________________


Subject:    Race condition in Oracle C Interface?
Author: Michael Haggerty <mhagger_at_alum.mit.edu>
Date:       11/19/00 3:00 PM



I am trying to use Oracle in a multithreaded application that creates
and destroys multiple database connections.  It seems to have tickled
a bug in Oracle, though, because the application hangs up deep in
Oracle.  I simplified the application into the trivial C program
appended below, which on my system locks up about half of the time.
It just opens up two database connections and some associated
structures and then closes them.  I don't think there is a problem
with code, but if you are sceptical just take a look; it is quite
trivial.



Has anybody seen this problem?  Does anyone know a workaround?



I am running Oracle 8.1.6.1 under Linux/Intel with kernel version
2.2.14.  The program locks up within OCIServerDetach and has to be
kill -6'ed or stronger.  Only the client seems to lock up; the server
seems unaffected.



Thanks,


Michael



--



Michael Haggerty


mhagger_at_alum.mit.edu


/* ==================== main.c ======================== */





/* compile with:


    gcc -I/ora8/m01/app/oracle/product/8.1.6/rdbms/demo


-I/ora8/m01/app/oracle/product/8.1.6/network/public

-I/ora8/m01/app/oracle/product/8.1.6/plsql/public

-I/ora8/m01/app/oracle/product/8.1.6/rdbms/public -DORACLE8i -g -o main



-L/ora8/m01/app/oracle/product/8.1.6/lib/ -lclntsh

-Wl,-rpath,/ora8/m01/app/oracle/product/8.1.6/lib ./main.c




*/


#include <assert.h>
#include <stdio.h>
#include <string.h>
#include <malloc.h>
#include <oci.h>


typedef struct {
        OCIEnv          *envhp;                 /* Environment handle   */
        OCIError        *errhp;                 /* Error handle         */
        OCIServer       *srvhp;                 /* Server handle        */
        OCISession      *usrhp;                 /* User handle          */
        OCISvcCtx       *svchp;                 /* Service Context      */


} ServerContext;




ServerContext *Connect(char *user, char *password, char *database) {

        ServerContext *sc;
        int     userlen;
        int     passwordlen;
        int     databaselen;
        sword   status;
        sword   credentials = OCI_CRED_RDBMS;

        userlen = strlen(user);
        passwordlen = strlen(password);
        databaselen = strlen(database);

        sc = (ServerContext *)malloc(sizeof(ServerContext));

        sc->envhp = NULL;
        sc->errhp = NULL;
        sc->svchp = NULL;
        sc->srvhp = NULL;
        sc->usrhp = NULL;

        status = OCIEnvCreate(&sc->envhp, OCI_THREADED, NULL, NULL, NULL, NULL,
                              0, NULL);
        assert(status == OCI_SUCCESS);

        /* Allocate the error handle */
        status = OCIHandleAlloc(sc->envhp, (dvoid **)&sc->errhp,
                                OCI_HTYPE_ERROR, 0, NULL);
        assert(status == OCI_SUCCESS);

        /* Allocate the server handle */
        status = OCIHandleAlloc(sc->envhp, (dvoid **) &sc->srvhp,
                                OCI_HTYPE_SERVER, 0, NULL);
        assert(status == OCI_SUCCESS);

        /* Connect to database */
        status = OCIServerAttach(sc->srvhp, sc->errhp, database, databaselen,
                                 OCI_DEFAULT);
        assert(status == OCI_SUCCESS);

        /* Allocate a service context */
        status = OCIHandleAlloc(sc->envhp, (dvoid **) &sc->svchp,
                                OCI_HTYPE_SVCCTX, 0, NULL);
        assert(status == OCI_SUCCESS);

        /* Attach the server to the service context */
        status = OCIAttrSet(sc->svchp, OCI_HTYPE_SVCCTX, (dvoid *) sc->srvhp,
                            (ub4) 0, OCI_ATTR_SERVER, sc->errhp);
        assert(status == OCI_SUCCESS);

        /* Allocate a session */
        status = OCIHandleAlloc(sc->envhp, (dvoid **) &sc->usrhp,
                                OCI_HTYPE_SESSION, 0, NULL);
        assert(status == OCI_SUCCESS);

        /* Were credentials provided? if so, set them in the session */
        status = OCIAttrSet(sc->usrhp, OCI_HTYPE_SESSION,
                            (dvoid *) user, (ub4) userlen,
                            OCI_ATTR_USERNAME, sc->errhp);
        assert(status == OCI_SUCCESS);

        status = OCIAttrSet(sc->usrhp, OCI_HTYPE_SESSION,
                            (dvoid *) password, (ub4) passwordlen,
                            OCI_ATTR_PASSWORD, sc->errhp);
        assert(status == OCI_SUCCESS);
        
        /* Now begin the session */
        status = OCISessionBegin(sc->svchp, sc->errhp, sc->usrhp,
                                 credentials, OCI_DEFAULT);
        assert(status == OCI_SUCCESS);

        /* Now attach the session to the service context */
        status = OCIAttrSet(sc->svchp, OCI_HTYPE_SVCCTX,
                            sc->usrhp, 0, OCI_ATTR_SESSION, sc->errhp);
        assert(status == OCI_SUCCESS);

        return sc;




}


/*
** ServerContext_dealloc
**
** Called when a server context goes out of scope; hang up the connection
** to the database!




*/



void ServerContext_dealloc(ServerContext *self) {


        sword status;


        /* End the session */
        assert(self->svchp);
        status = OCISessionEnd(self->svchp, self->errhp, self->usrhp,
                               OCI_DEFAULT);
        assert(status == OCI_SUCCESS);

        /* Disconnect from the server */
        assert(self->srvhp);
        status = OCIServerDetach(self->srvhp, self->errhp, OCI_DEFAULT);
        assert(status == OCI_SUCCESS);

        /* Deallocate the session handle */
        assert(self->usrhp);
        status = OCIHandleFree(self->usrhp, OCI_HTYPE_SESSION);
        assert(status == OCI_SUCCESS);

        /* Deallocate the server handle */
        assert(self->srvhp);
        status = OCIHandleFree(self->srvhp, OCI_HTYPE_SERVER);
        assert(status == OCI_SUCCESS);

        /* Deallocate the service context handle */
        assert(self->svchp);
        status = OCIHandleFree(self->svchp, OCI_HTYPE_SVCCTX);
        assert(status == OCI_SUCCESS);

        /* Deallocate the error handle */
        assert(self->errhp);
        status = OCIHandleFree(self->errhp, OCI_HTYPE_ERROR);
        assert(status == OCI_SUCCESS);

        /* Deallocate the environment handle */
        assert(self->envhp);
        status = OCIHandleFree(self->envhp, OCI_HTYPE_ENV);
        assert(status == OCI_SUCCESS);

        free(self);




}



int main(int argc, char *argv[]) {

    char *user;
    char *password;
    char *database;




    ServerContext *db1;


    ServerContext *db2;


    assert(argc == 4);


    user = argv[1];


    password = argv[2];


    database = argv[3];


    db1 = Connect(user, password, database);
    db2 = Connect(user, password, database);
    fprintf(stderr, "Deleting db2.\n");


    ServerContext_dealloc(db2);


    fprintf(stderr, "Deleting db1.\n");


    ServerContext_dealloc(db1);


    fprintf(stderr, "This line often not reached.\n");
    return 0;


}



-- 



Please see the official ORACLE-L FAQ: http://www.orafaq.com


-- 



Author: Michael Haggerty


  INET: mhagger_at_alum.mit.edu


Fat City Network Services    -- (858) 538-5051  FAX: (858) 538-5051
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