[citadel.git] / citadel / threads.c

/*
 * Thread handling stuff for Citadel server
 *
 * Copyright (c) 1987-2011 by the citadel.org team
 *
 * This program is open source software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with this program; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */

#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/types.h>
#include <errno.h>
#include <sys/socket.h>
#include <unistd.h>
#include <fcntl.h>
#include <signal.h>
#include <syslog.h>

#include "sysdep.h"
#if TIME_WITH_SYS_TIME
# include <sys/time.h>
# include <time.h>
#else
# if HAVE_SYS_TIME_H
#  include <sys/time.h>
# else
#  include <time.h>
# endif
#endif

#ifdef HAVE_SYSCALL_H
# include <syscall.h>
#else 
# if HAVE_SYS_SYSCALL_H
#  include <sys/syscall.h>
# endif
#endif

#include <libcitadel.h>

#include "threads.h"
#include "ctdl_module.h"
#include "modules_init.h"
#include "housekeeping.h"
#include "config.h"
#include "citserver.h"
#include "sysdep_decls.h"
#include "context.h"


/*
 * To create a thread you must call one of the create thread functions.
 * You must pass it the address of (a pointer to a CtdlThreadNode initialised to NULL) like this
 * struct CtdlThreadNode *node = NULL;
 * pass in &node
 * If the thread is created *node will point to the thread control structure for the created thread.
 * If the thread creation fails *node remains NULL
 * Do not free the memory pointed to by *node, it doesn't belong to you.
 * This new interface duplicates much of the eCrash stuff. We should go for closer integration since that would
 * remove the need for the calls to eCrashRegisterThread and friends
 */

static int num_threads = 0;                     /* Current number of threads */
static int num_workers = 0;                     /* Current number of worker threads */

CtdlThreadNode *CtdlThreadList = NULL;
CtdlThreadNode *CtdlThreadSchedList = NULL;

static CtdlThreadNode *GC_thread = NULL;
static char *CtdlThreadStates[CTDL_THREAD_LAST_STATE];
double CtdlThreadLoadAvg = 0;
double CtdlThreadWorkerAvg = 0;
citthread_key_t ThreadKey;

citthread_mutex_t Critters[MAX_SEMAPHORES];     /* Things needing locking */



void InitialiseSemaphores(void)
{
        int i;

        /* Set up a bunch of semaphores to be used for critical sections */
        for (i=0; i<MAX_SEMAPHORES; ++i) {
                citthread_mutex_init(&Critters[i], NULL);
        }
}




/*
 * Obtain a semaphore lock to begin a critical section.
 * but only if no one else has one
 */
int try_critical_section(int which_one)
{
        /* For all types of critical sections except those listed here,
         * ensure nobody ever tries to do a critical section within a
         * transaction; this could lead to deadlock.
         */
        if (    (which_one != S_FLOORCACHE)
                && (which_one != S_RPLIST)
        ) {
                cdb_check_handles();
        }
        return (citthread_mutex_trylock(&Critters[which_one]));
}


/*
 * Obtain a semaphore lock to begin a critical section.
 */
void begin_critical_section(int which_one)
{
        /* syslog(LOG_DEBUG, "begin_critical_section(%d)\n", which_one); */

        /* For all types of critical sections except those listed here,
         * ensure nobody ever tries to do a critical section within a
         * transaction; this could lead to deadlock.
         */
        if (    (which_one != S_FLOORCACHE)
                && (which_one != S_RPLIST)
        ) {
                cdb_check_handles();
        }
        citthread_mutex_lock(&Critters[which_one]);
}

/*
 * Release a semaphore lock to end a critical section.
 */
void end_critical_section(int which_one)
{
        citthread_mutex_unlock(&Critters[which_one]);
}


/*
 * A function to destroy the TSD
 */
static void ctdl_thread_internal_dest_tsd(void *arg)
{
        if (arg != NULL) {
                check_handles(arg);
                free(arg);
        }
}


/*
 * A function to initialise the thread TSD
 */
void ctdl_thread_internal_init_tsd(void)
{
        int ret;
        
        if ((ret = citthread_key_create(&ThreadKey, ctdl_thread_internal_dest_tsd))) {
                syslog(LOG_EMERG, "citthread_key_create: %s\n", strerror(ret));
                exit(CTDLEXIT_DB);
        }
}

/*
 * Ensure that we have a key for thread-specific data. 
 *
 * This should be called immediately after startup by any thread 
 * 
 */
void CtdlThreadAllocTSD(void)
{
        ThreadTSD *tsd;

        if (citthread_getspecific(ThreadKey) != NULL)
                return;

        tsd = malloc(sizeof(ThreadTSD));

        tsd->tid = NULL;

        memset(tsd->cursors, 0, sizeof tsd->cursors);
        tsd->self = NULL;
        
        citthread_setspecific(ThreadKey, tsd);
}


void ctdl_thread_internal_free_tsd(void)
{
        ctdl_thread_internal_dest_tsd(citthread_getspecific(ThreadKey));
        citthread_setspecific(ThreadKey, NULL);
}


void ctdl_thread_internal_cleanup(void)
{
        int i;
        CtdlThreadNode *this_thread, *that_thread;
        
        for (i=0; i<CTDL_THREAD_LAST_STATE; i++)
        {
                free (CtdlThreadStates[i]);
        }
        
        /* Clean up the scheduled thread list */
        this_thread = CtdlThreadSchedList;
        while (this_thread)
        {
                that_thread = this_thread;
                this_thread = this_thread->next;
                citthread_mutex_destroy(&that_thread->ThreadMutex);
                citthread_cond_destroy(&that_thread->ThreadCond);
                citthread_mutex_destroy(&that_thread->SleepMutex);
                citthread_cond_destroy(&that_thread->SleepCond);
                citthread_attr_destroy(&that_thread->attr);
                free(that_thread);
        }
        ctdl_thread_internal_free_tsd();
}

void ctdl_thread_internal_init(void)
{
        CtdlThreadNode *this_thread;
        int ret = 0;
        
        CtdlThreadStates[CTDL_THREAD_INVALID] = strdup ("Invalid Thread");
        CtdlThreadStates[CTDL_THREAD_VALID] = strdup("Valid Thread");
        CtdlThreadStates[CTDL_THREAD_CREATE] = strdup("Thread being Created");
        CtdlThreadStates[CTDL_THREAD_CANCELLED] = strdup("Thread Cancelled");
        CtdlThreadStates[CTDL_THREAD_EXITED] = strdup("Thread Exited");
        CtdlThreadStates[CTDL_THREAD_STOPPING] = strdup("Thread Stopping");
        CtdlThreadStates[CTDL_THREAD_STOP_REQ] = strdup("Thread Stop Requested");
        CtdlThreadStates[CTDL_THREAD_SLEEPING] = strdup("Thread Sleeping");
        CtdlThreadStates[CTDL_THREAD_RUNNING] = strdup("Thread Running");
        CtdlThreadStates[CTDL_THREAD_BLOCKED] = strdup("Thread Blocked");
        
        /* Get ourself a thread entry */
        this_thread = malloc(sizeof(CtdlThreadNode));
        if (this_thread == NULL) {
                syslog(LOG_EMERG, "Thread system, can't allocate CtdlThreadNode, exiting\n");
                return;
        }
        // Ensuring this is zero'd means we make sure the thread doesn't start doing its thing until we are ready.
        memset (this_thread, 0, sizeof(CtdlThreadNode));
        
        citthread_mutex_init (&(this_thread->ThreadMutex), NULL);
        citthread_cond_init (&(this_thread->ThreadCond), NULL);
        citthread_mutex_init (&(this_thread->SleepMutex), NULL);
        citthread_cond_init (&(this_thread->SleepCond), NULL);
        
        /* We are garbage collector so create us as running */
        this_thread->state = CTDL_THREAD_RUNNING;
        
        if ((ret = citthread_attr_init(&this_thread->attr))) {
                syslog(LOG_EMERG, "Thread system, citthread_attr_init: %s\n", strerror(ret));
                free(this_thread);
                return;
        }

        this_thread->name = "Garbage Collection Thread";
        
        this_thread->tid = citthread_self();
        GC_thread = this_thread;
        CT = this_thread;
        
        num_threads++;  // Increase the count of threads in the system.

        this_thread->next = CtdlThreadList;
        CtdlThreadList = this_thread;
        if (this_thread->next)
                this_thread->next->prev = this_thread;
        /* Set up start times */
        gettimeofday(&this_thread->start_time, NULL);           /* Time this thread started */
        memcpy(&this_thread->last_state_change, &this_thread->start_time, sizeof (struct timeval));     /* Changed state so mark it. */
}


/*
 * A function to chenge the state of a thread
 */
void ctdl_thread_internal_change_state (CtdlThreadNode *this_thread, enum CtdlThreadState new_state)
{
        /*
         * Wether we change state or not we need update the load values
         */
        /* This mutex not needed here? */
        citthread_mutex_lock(&this_thread->ThreadMutex); /* To prevent race condition of a sleeping thread */
        if ((new_state == CTDL_THREAD_STOP_REQ) && (this_thread->state > CTDL_THREAD_STOP_REQ))
                this_thread->state = new_state;
        if (((new_state == CTDL_THREAD_SLEEPING) || (new_state == CTDL_THREAD_BLOCKED)) && (this_thread->state == CTDL_THREAD_RUNNING))
                this_thread->state = new_state;
        if ((new_state == CTDL_THREAD_RUNNING) && ((this_thread->state == CTDL_THREAD_SLEEPING) || (this_thread->state == CTDL_THREAD_BLOCKED)))
                this_thread->state = new_state;
        citthread_mutex_unlock(&this_thread->ThreadMutex);
}


/*
 * A function to tell all threads to exit
 */
void CtdlThreadStopAll(void)
{
        /* First run any registered shutdown hooks.  This probably doesn't belong here. */
        PerformSessionHooks(EVT_SHUTDOWN);
        
        /* then close all tcp ports so nobody else can talk to us anymore. */
        CtdlShutdownServiceHooks();
        //FIXME: The signalling of the condition should not be in the critical_section
        // We need to build a list of threads we are going to signal and then signal them afterwards
        
        CtdlThreadNode *this_thread;
        
        begin_critical_section(S_THREAD_LIST);
        this_thread = CtdlThreadList;
        // Ask the GC thread to stop first so everything knows we are shutting down.
        GC_thread->state = CTDL_THREAD_STOP_REQ;
        while(this_thread)
        {
                if (!citthread_equal(this_thread->tid, GC_thread->tid))
                        citthread_kill(this_thread->tid, SIGHUP);

                ctdl_thread_internal_change_state (this_thread, CTDL_THREAD_STOP_REQ);
                citthread_cond_signal(&this_thread->ThreadCond);
                citthread_cond_signal(&this_thread->SleepCond);
                this_thread->stop_ticker = time(NULL);
                syslog(LOG_DEBUG, "Thread system stopping thread \"%s\" (0x%08lx).\n",
                        this_thread->name, this_thread->tid);
                this_thread = this_thread->next;
        }
        end_critical_section(S_THREAD_LIST);
}


/*
 * A function to wake up all sleeping threads
 */
void CtdlThreadWakeAll(void)
{
        CtdlThreadNode *this_thread;
        
        syslog(LOG_DEBUG, "Thread system waking all threads.\n");
        
        begin_critical_section(S_THREAD_LIST);
        this_thread = CtdlThreadList;
        while(this_thread)
        {
                if (!this_thread->thread_func)
                {
                        citthread_cond_signal(&this_thread->ThreadCond);
                        citthread_cond_signal(&this_thread->SleepCond);
                }
                this_thread = this_thread->next;
        }
        end_critical_section(S_THREAD_LIST);
}


/*
 * A function to return the number of threads running in the system
 */
int CtdlThreadGetCount(void)
{
        return  num_threads;
}

int CtdlThreadGetWorkers(void)
{
        return  num_workers;
}

double CtdlThreadGetWorkerAvg(void)
{
        double ret;
        
        begin_critical_section(S_THREAD_LIST);
        ret =  CtdlThreadWorkerAvg;
        end_critical_section(S_THREAD_LIST);
        return ret;
}

double CtdlThreadGetLoadAvg(void)
{
        double load_avg[3] = {0.0, 0.0, 0.0};

        int ret = 0;
        int smp_num_cpus;

        /* Borrowed this straight from procps */
        smp_num_cpus = sysconf(_SC_NPROCESSORS_ONLN);
        if(smp_num_cpus<1) smp_num_cpus=1; /* SPARC glibc is buggy */

#ifdef HAVE_GETLOADAVG
        ret = getloadavg(load_avg, 3);
#endif
        if (ret < 0)
                return 0;
        return load_avg[0] / smp_num_cpus;
/*
 * This old chunk of code return a value that indicated the load on citserver
 * This value could easily reach 100 % even when citserver was doing very little and
 * hence the machine has much more spare capacity.
 * Because this value was used to determine if the machine was under heavy load conditions
 * from other processes in the system then citserver could be strangled un-necesarily
 * What we are actually trying to achieve is to strangle citserver if the machine is heavily loaded.
 * So we have changed this.

        begin_critical_section(S_THREAD_LIST);
        ret =  CtdlThreadLoadAvg;
        end_critical_section(S_THREAD_LIST);
        return ret;
*/
}




/*
 * A function to rename a thread
 * Returns a const char *
 */
const char *CtdlThreadName(const char *name)
{
        const char *old_name;
        
        if (!CT)
        {
                syslog(LOG_WARNING, "Thread system WARNING. Attempt to CtdlThreadRename() a non thread. %s\n", name);
                return NULL;
        }
        old_name = CT->name;
        if (name)
                CT->name = name;
        return (old_name);
}       


/*
 * A function to force a thread to exit
 */
void CtdlThreadCancel(CtdlThreadNode *thread)
{
        CtdlThreadNode *this_thread;
        
        if (!thread)
                this_thread = CT;
        else
                this_thread = thread;
        if (!this_thread)
        {
                syslog(LOG_EMERG, "Thread system PANIC. Attempt to CtdlThreadCancel() a non thread.\n");
                CtdlThreadStopAll();
                return;
        }
        
        if (!this_thread->thread_func)
        {
                syslog(LOG_EMERG, "Thread system PANIC. Attempt to CtdlThreadCancel() the garbage collector.\n");
                CtdlThreadStopAll();
                return;
        }
        
        ctdl_thread_internal_change_state (this_thread, CTDL_THREAD_CANCELLED);
        citthread_cancel(this_thread->tid);
}


/*
 * A function for a thread to check if it has been asked to stop
 */
int CtdlThreadCheckStop(void)
{
        int state;
        
        if (!CT)
        {
                syslog(LOG_EMERG, "Thread system PANIC, CtdlThreadCheckStop() called by a non thread.\n");
                CtdlThreadStopAll();
                return -1;
        }
        
        state = CT->state;

        if (CT->signal)
        {
                syslog(LOG_DEBUG, "Thread \"%s\" caught signal %d.\n", CT->name, CT->signal);
                if (CT->signal == SIGHUP)
                        CT->state = CTDL_THREAD_STOP_REQ;
                CT->signal = 0;
        }
        if(state == CTDL_THREAD_STOP_REQ)
        {
                CT->state = CTDL_THREAD_STOPPING;
                return -1;
        }
        else if((state < CTDL_THREAD_STOP_REQ) && (state > CTDL_THREAD_CREATE))
        {
                return -1;
        }
        return 0;
}


/*
 * A function to ask a thread to exit
 * The thread must call CtdlThreadCheckStop() periodically to determine if it should exit
 */
void CtdlThreadStop(CtdlThreadNode *thread)
{
        CtdlThreadNode *this_thread;
        
        if (!thread)
                this_thread = CT;
        else
                this_thread = thread;
        if (!this_thread)
                return;
        if (!(this_thread->thread_func))
                return;         // Don't stop garbage collector

        if (!citthread_equal(this_thread->tid, GC_thread->tid))
                citthread_kill(this_thread->tid, SIGHUP);

        ctdl_thread_internal_change_state (this_thread, CTDL_THREAD_STOP_REQ);
        citthread_cond_signal(&this_thread->ThreadCond);
        citthread_cond_signal(&this_thread->SleepCond);
        this_thread->stop_ticker = time(NULL);
}

/*
 * So we now have a sleep command that works with threads but it is in seconds
 */
void CtdlThreadSleep(int secs)
{
        struct timespec wake_time;
        struct timeval time_now;
        
        
        if (!CT)
        {
                syslog(LOG_WARNING, "CtdlThreadSleep() called by something that is not a thread. Should we die?\n");
                return;
        }
        
        memset (&wake_time, 0, sizeof(struct timespec));
        gettimeofday(&time_now, NULL);
        wake_time.tv_sec = time_now.tv_sec + secs;
        wake_time.tv_nsec = time_now.tv_usec * 10;

        ctdl_thread_internal_change_state (CT, CTDL_THREAD_SLEEPING);
        
        citthread_mutex_lock(&CT->ThreadMutex); /* Prevent something asking us to awaken before we've gone to sleep */
        citthread_cond_timedwait(&CT->SleepCond, &CT->ThreadMutex, &wake_time);
        citthread_mutex_unlock(&CT->ThreadMutex);
        
        ctdl_thread_internal_change_state (CT, CTDL_THREAD_RUNNING);
}


/*
 * Routine to clean up our thread function on exit
 */
static void ctdl_internal_thread_cleanup(void *arg)
{
        /*
         * In here we were called by the current thread because it is exiting
         * NB. WE ARE THE CURRENT THREAD
         */
        if (CT)
        {
                const char *name = CT->name;
                const pid_t tid = CT->tid;

                syslog(LOG_NOTICE, "Thread \"%s\" (0x%08lx) exited.\n", name, (unsigned long) tid);
        }
        else 
        {
                syslog(LOG_NOTICE, "some ((unknown ? ? ?) Thread exited.\n");
        }
        
        #ifdef HAVE_BACKTRACE
///     eCrash_UnregisterThread();
        #endif
        
        citthread_mutex_lock(&CT->ThreadMutex);
        CT->state = CTDL_THREAD_EXITED; // needs to be last thing else house keeping will unlink us too early
        citthread_mutex_unlock(&CT->ThreadMutex);
}

/*
 * Garbage collection routine.
 * Gets called by main() in a loop to clean up the thread list periodically.
 */
void CtdlThreadGC (void)
{


        return;
        /* FIXME this is a big deal, but I think it's causing corruption */


        CtdlThreadNode *this_thread, *that_thread;
        int workers = 0, sys_workers;
        int ret=0;

        begin_critical_section(S_THREAD_LIST);
        
        /* Handle exiting of garbage collector thread */
        if(num_threads == 1)
                CtdlThreadList->state = CTDL_THREAD_EXITED;
        
#ifdef WITH_THREADLOG
        syslog(LOG_DEBUG, "Thread system running garbage collection.\n");
#endif
        /*
         * Woke up to do garbage collection
         */
        this_thread = CtdlThreadList;
        while(this_thread)
        {
                that_thread = this_thread;
                this_thread = this_thread->next;
                
                if ((that_thread->state == CTDL_THREAD_STOP_REQ || that_thread->state == CTDL_THREAD_STOPPING)
                        && (!citthread_equal(that_thread->tid, citthread_self())))
                {
                        syslog(LOG_DEBUG, "Waiting for thread %s (0x%08lx) to exit.\n", that_thread->name, that_thread->tid);
                        terminate_stuck_sessions();
                }
                else
                {
                        /**
                         * Catch the situation where a worker was asked to stop but couldn't and we are not
                         * shutting down.
                         */
                        that_thread->stop_ticker = 0;
                }
                
                if (that_thread->stop_ticker + 5 == time(NULL))
                {
                        syslog(LOG_DEBUG, "Thread System: The thread \"%s\" (0x%08lx) failed to self terminate within 5 ticks. It would be cancelled now.\n", that_thread->name, that_thread->tid);
                        if ((that_thread->flags & CTDLTHREAD_WORKER) == 0)
                                syslog(LOG_INFO, "Thread System: A non worker thread would have been canceled this may cause message loss.\n");
//                      that_thread->state = CTDL_THREAD_CANCELLED;
                        that_thread->stop_ticker++;
//                      citthread_cancel(that_thread->tid);
//                      continue;
                }
                
                /* Do we need to clean up this thread? */
                if ((that_thread->state != CTDL_THREAD_EXITED) && (that_thread->state != CTDL_THREAD_CANCELLED))
                {
                        if(that_thread->flags & CTDLTHREAD_WORKER)
                                workers++;      /* Sanity check on number of worker threads */
                        continue;
                }
                
                if (citthread_equal(that_thread->tid, citthread_self()) && that_thread->thread_func)
                {       /* Sanity check */
                        end_critical_section(S_THREAD_LIST);
                        syslog(LOG_EMERG, "Thread system PANIC, a thread is trying to clean up after itself.\n");
                        abort();
                        return;
                }
                
                if (num_threads <= 0)
                {       /* Sanity check */
                        end_critical_section(S_THREAD_LIST);
                        syslog(LOG_EMERG, "Thread system PANIC, num_threads <= 0 and trying to do Garbage Collection.\n");
                        abort();
                        return;
                }

                if(that_thread->flags & CTDLTHREAD_WORKER)
                        num_workers--;  /* This is a wroker thread so reduce the count. */
                num_threads--;
                /* If we are unlinking the list head then the next becomes the list head */
                if(that_thread->prev)
                        that_thread->prev->next = that_thread->next;
                else
                        CtdlThreadList = that_thread->next;
                if(that_thread->next)
                        that_thread->next->prev = that_thread->prev;
                
                citthread_cond_signal(&that_thread->ThreadCond);
                citthread_cond_signal(&that_thread->SleepCond); // Make sure this thread is awake
                citthread_mutex_lock(&that_thread->ThreadMutex);        // Make sure it has done what its doing
                citthread_mutex_unlock(&that_thread->ThreadMutex);
                /*
                 * Join on the thread to do clean up and prevent memory leaks
                 * Also makes sure the thread has cleaned up after itself before we remove it from the list
                 * We can join on the garbage collector thread the join should just return EDEADLCK
                 */
                ret = citthread_join (that_thread->tid, NULL);
                if (ret == EDEADLK)
                        syslog(LOG_DEBUG, "Garbage collection on own thread.\n");
                else if (ret == EINVAL)
                        syslog(LOG_DEBUG, "Garbage collection, that thread already joined on.\n");
                else if (ret == ESRCH)
                        syslog(LOG_DEBUG, "Garbage collection, no thread to join on.\n");
                else if (ret != 0)
                        syslog(LOG_DEBUG, "Garbage collection, citthread_join returned an unknown error(%d).\n", ret);
                /*
                 * Now we own that thread entry
                 */
                syslog(LOG_INFO, "Garbage Collection for thread \"%s\" (0x%08lx).\n",
                        that_thread->name, that_thread->tid);
                citthread_mutex_destroy(&that_thread->ThreadMutex);
                citthread_cond_destroy(&that_thread->ThreadCond);
                citthread_mutex_destroy(&that_thread->SleepMutex);
                citthread_cond_destroy(&that_thread->SleepCond);
                citthread_attr_destroy(&that_thread->attr);
                free(that_thread);
        }
        sys_workers = num_workers;
        end_critical_section(S_THREAD_LIST);
        
        /* Sanity check number of worker threads */
        if (workers != sys_workers)
        {
                syslog(LOG_EMERG,
                        "Thread system PANIC, discrepancy in number of worker threads. Counted %d, should be %d.\n",
                        workers, sys_workers
                        );
                abort();
        }
}



 
/*
 * Runtime function for a Citadel Thread.
 * This initialises the threads environment and then calls the user supplied thread function
 * Note that this is the REAL thread function and wraps the users thread function.
 */ 
static void *ctdl_internal_thread_func (void *arg)
{
        CtdlThreadNode *this_thread;
        void *ret = NULL;

        /* lock and unlock the thread list.
         * This causes this thread to wait until all its creation stuff has finished before it
         * can continue its execution.
         */
        begin_critical_section(S_THREAD_LIST);
        this_thread = (CtdlThreadNode *) arg;
        gettimeofday(&this_thread->start_time, NULL);           /* Time this thread started */
        
        // Register the cleanup function to take care of when we exit.
        citthread_cleanup_push(ctdl_internal_thread_cleanup, NULL);
        // Get our thread data structure
        CtdlThreadAllocTSD();
        CT = this_thread;
        this_thread->pid = getpid();
        memcpy(&this_thread->last_state_change, &this_thread->start_time, sizeof (struct timeval));     /* Changed state so mark it. */
        /* Only change to running state if we weren't asked to stop during the create cycle
         * Other wise there is a window to allow this threads creation to continue to full grown and
         * therby prevent a shutdown of the server.
         */
        if (!CtdlThreadCheckStop())
        {
                citthread_mutex_lock(&this_thread->ThreadMutex);
                this_thread->state = CTDL_THREAD_RUNNING;
                citthread_mutex_unlock(&this_thread->ThreadMutex);
        }
        end_critical_section(S_THREAD_LIST);
        
        // Register for tracing
        #ifdef HAVE_BACKTRACE
///     eCrash_RegisterThread(this_thread->name, 0);
        #endif
        
        // Tell the world we are here
#if defined(HAVE_SYSCALL_H) && defined (SYS_gettid)
        this_thread->reltid = syscall(SYS_gettid);
#endif
        syslog(LOG_NOTICE, "Created a new thread \"%s\" (0x%08lx).\n",
                this_thread->name, this_thread->tid);
        
        /*
         * run the thread to do the work but only if we haven't been asked to stop
         */
        if (!CtdlThreadCheckStop())
                ret = (this_thread->thread_func)(this_thread->user_args);
        
        /*
         * Our thread is exiting either because it wanted to end or because the server is stopping
         * We need to clean up
         */
        citthread_cleanup_pop(1);       // Execute our cleanup routine and remove it
        
        return(ret);
}




/*
 * Function to initialise an empty thread structure
 */
CtdlThreadNode *ctdl_internal_init_thread_struct(CtdlThreadNode *this_thread, long flags)
{
        int ret = 0;
        
        // Ensuring this is zero'd means we make sure the thread doesn't start doing its thing until we are ready.
        memset (this_thread, 0, sizeof(CtdlThreadNode));
        
        /* Create the mutex's early so we can use them */
        citthread_mutex_init (&(this_thread->ThreadMutex), NULL);
        citthread_cond_init (&(this_thread->ThreadCond), NULL);
        citthread_mutex_init (&(this_thread->SleepMutex), NULL);
        citthread_cond_init (&(this_thread->SleepCond), NULL);
        
        this_thread->state = CTDL_THREAD_CREATE;
        
        if ((ret = citthread_attr_init(&this_thread->attr))) {
                citthread_mutex_unlock(&this_thread->ThreadMutex);
                citthread_mutex_destroy(&(this_thread->ThreadMutex));
                citthread_cond_destroy(&(this_thread->ThreadCond));
                citthread_mutex_destroy(&(this_thread->SleepMutex));
                citthread_cond_destroy(&(this_thread->SleepCond));
                syslog(LOG_EMERG, "Thread system, citthread_attr_init: %s\n", strerror(ret));
                free(this_thread);
                return NULL;
        }

        /* Our per-thread stacks need to be bigger than the default size,
         * otherwise the MIME parser crashes on FreeBSD, and the IMAP service
         * crashes on 64-bit Linux.
         */
        if (flags & CTDLTHREAD_BIGSTACK)
        {
#ifdef WITH_THREADLOG
                syslog(LOG_INFO, "Thread system. Creating BIG STACK thread.\n");
#endif
                if ((ret = citthread_attr_setstacksize(&this_thread->attr, THREADSTACKSIZE))) {
                        citthread_mutex_unlock(&this_thread->ThreadMutex);
                        citthread_mutex_destroy(&(this_thread->ThreadMutex));
                        citthread_cond_destroy(&(this_thread->ThreadCond));
                        citthread_mutex_destroy(&(this_thread->SleepMutex));
                        citthread_cond_destroy(&(this_thread->SleepCond));
                        citthread_attr_destroy(&this_thread->attr);
                        syslog(LOG_EMERG, "Thread system, citthread_attr_setstacksize: %s\n",
                                strerror(ret));
                        free(this_thread);
                        return NULL;
                }
        }

        /* Set this new thread with an avg_blocked of 2. We do this so that its creation affects the
         * load average for the system. If we don't do this then we create a mass of threads at the same time 
         * because the creation didn't affect the load average.
         */
        this_thread->avg_blocked = 2;
        
        return (this_thread);
}



 
/*
 * Internal function to create a thread.
 */ 
CtdlThreadNode *ctdl_internal_create_thread(char *name, long flags, void *(*thread_func) (void *arg), void *args)
{
        int ret = 0;
        CtdlThreadNode *this_thread;

        if (num_threads >= 32767)
        {
                syslog(LOG_EMERG, "Thread system. Thread list full.\n");
                return NULL;
        }
                
        this_thread = malloc(sizeof(CtdlThreadNode));
        if (this_thread == NULL) {
                syslog(LOG_EMERG, "Thread system, can't allocate CtdlThreadNode, exiting\n");
                return NULL;
        }
        
        /* Initialise the thread structure */
        if (ctdl_internal_init_thread_struct(this_thread, flags) == NULL)
        {
                free(this_thread);
                syslog(LOG_EMERG, "Thread system, can't initialise CtdlThreadNode, exiting\n");
                return NULL;
        }
        /*
         * If we got here we are going to create the thread so we must initilise the structure
         * first because most implimentations of threading can't create it in a stopped state
         * and it might want to do things with its structure that aren't initialised otherwise.
         */
        if(name)
        {
                this_thread->name = name;
        }
        else
        {
                this_thread->name = "Un-named Thread";
        }
        
        this_thread->flags = flags;
        this_thread->thread_func = thread_func;
        this_thread->user_args = args;
        
        begin_critical_section(S_THREAD_LIST);
        /*
         * We pass this_thread into the thread as its args so that it can find out information
         * about itself and it has a bit of storage space for itself, not to mention that the REAL
         * thread function needs to finish off the setup of the structure
         */
        if ((ret = citthread_create(&this_thread->tid, &this_thread->attr, ctdl_internal_thread_func, this_thread) != 0))
        {
                end_critical_section(S_THREAD_LIST);
                syslog(LOG_ALERT, "Thread system, Can't create thread: %s\n",
                        strerror(ret));
                citthread_mutex_unlock(&this_thread->ThreadMutex);
                citthread_mutex_destroy(&(this_thread->ThreadMutex));
                citthread_cond_destroy(&(this_thread->ThreadCond));
                citthread_mutex_destroy(&(this_thread->SleepMutex));
                citthread_cond_destroy(&(this_thread->SleepCond));
                citthread_attr_destroy(&this_thread->attr);
                free(this_thread);
                return NULL;
        }
        num_threads++;  // Increase the count of threads in the system.
        if(this_thread->flags & CTDLTHREAD_WORKER)
                num_workers++;

        this_thread->next = CtdlThreadList;
        CtdlThreadList = this_thread;
        if (this_thread->next)
                this_thread->next->prev = this_thread;
        
        end_critical_section(S_THREAD_LIST);
        
        return this_thread;
}

/*
 * Wrapper function to create a thread
 * ensures the critical section and other protections are in place.
 * char *name = name to give to thread, if NULL, use generic name
 * int flags = flags to determine type of thread and standard facilities
 */
CtdlThreadNode *CtdlThreadCreate(char *name, long flags, void *(*thread_func) (void *arg), void *args)
{
        CtdlThreadNode *ret = NULL;
        
        ret = ctdl_internal_create_thread(name, flags, thread_func, args);
        return ret;
}



CtdlThreadNode *ctdl_thread_internal_start_scheduled (CtdlThreadNode *this_thread)
{
        int ret = 0;
        
        begin_critical_section(S_THREAD_LIST);
        /*
         * We pass this_thread into the thread as its args so that it can find out information
         * about itself and it has a bit of storage space for itself, not to mention that the REAL
         * thread function needs to finish off the setup of the structure
         */
        if ((ret = citthread_create(&this_thread->tid, &this_thread->attr, ctdl_internal_thread_func, this_thread) != 0))
        {
                end_critical_section(S_THREAD_LIST);
                syslog(LOG_DEBUG, "Failed to start scheduled thread \"%s\": %s\n", this_thread->name, strerror(ret));
                citthread_mutex_destroy(&(this_thread->ThreadMutex));
                citthread_cond_destroy(&(this_thread->ThreadCond));
                citthread_mutex_destroy(&(this_thread->SleepMutex));
                citthread_cond_destroy(&(this_thread->SleepCond));
                citthread_attr_destroy(&this_thread->attr);
                free(this_thread);
                return NULL;
        }
        
        
        num_threads++;  // Increase the count of threads in the system.
        if(this_thread->flags & CTDLTHREAD_WORKER)
                num_workers++;

        this_thread->next = CtdlThreadList;
        CtdlThreadList = this_thread;
        if (this_thread->next)
                this_thread->next->prev = this_thread;
        
        end_critical_section(S_THREAD_LIST);
        
        
        return this_thread;
}



void ctdl_thread_internal_check_scheduled(void)
{
        CtdlThreadNode *this_thread, *that_thread;
        time_t now;
        
        /* Don't start scheduled threads if the system wants single user mode */
        if (CtdlWantSingleUser())
                return;
        
        if (try_critical_section(S_SCHEDULE_LIST))
                return; /* If this list is locked we wait till the next chance */
        
        now = time(NULL);
        
#ifdef WITH_THREADLOG
        syslog(LOG_DEBUG, "Checking for scheduled threads to start.\n");
#endif

        this_thread = CtdlThreadSchedList;
        while(this_thread)
        {
                that_thread = this_thread;
                this_thread = this_thread->next;
                
                if (now > that_thread->when)
                {
                        /* Unlink from schedule list */
                        if (that_thread->prev)
                                that_thread->prev->next = that_thread->next;
                        else
                                CtdlThreadSchedList = that_thread->next;
                        if (that_thread->next)
                                that_thread->next->prev = that_thread->prev;
                                
                        that_thread->next = that_thread->prev = NULL;
#ifdef WITH_THREADLOG
                        syslog(LOG_DEBUG, "About to start scheduled thread \"%s\".\n", that_thread->name);
#endif
                        if (CT->state > CTDL_THREAD_STOP_REQ)
                        {       /* Only start it if the system is not stopping */
                                if (ctdl_thread_internal_start_scheduled (that_thread))
                                {
#ifdef WITH_THREADLOG
                                        syslog(LOG_INFO, "Thread system, Started a scheduled thread \"%s\" (0x%08lx).\n",
                                                that_thread->name, that_thread->tid);
#endif
                                }
                        }
                }
#ifdef WITH_THREADLOG
                else
                {
                        syslog(LOG_DEBUG, "Thread \"%s\" will start in %ld seconds.\n",
                                that_thread->name, that_thread->when - time(NULL));
                }
#endif
        }
        end_critical_section(S_SCHEDULE_LIST);
}


/*
 * A warapper function for select so we can show a thread as blocked
 */
int CtdlThreadSelect(int n, fd_set *readfds, fd_set *writefds, fd_set *exceptfds, struct timeval *timeout)
{
        int ret = 0;
        
        ctdl_thread_internal_change_state(CT, CTDL_THREAD_BLOCKED);
        if (!CtdlThreadCheckStop())
                ret = select(n, readfds, writefds, exceptfds, timeout);
        /**
         * If the select returned <= 0 then it failed due to an error
         * or timeout so this thread could stop if asked to do so.
         * Anything else means it needs to continue unless the system is shutting down
         */
        if (ret > 0)
        {
                /**
                 * The select says this thread needs to do something useful.
                 * This thread was in an idle state so it may have been asked to stop
                 * but if the system isn't shutting down this thread is no longer
                 * idle and select has given it a task to do so it must not stop
                 * In this condition we need to force it into the running state.
                 * CtdlThreadGC will clear its ticker for us.
                 *
                 * FIXME: there is still a small hole here. It is possible for the sequence of locking
                 * to allow the state to get changed to STOP_REQ just after this code if the other thread
                 * has decided to change the state before this lock, it there fore has to wait till the lock
                 * completes but it will continue to change the state. We need something a bit better here.
                 */
                citthread_mutex_lock(&CT->ThreadMutex); /* To prevent race condition of a sleeping thread */
                if (GC_thread->state > CTDL_THREAD_STOP_REQ && CT->state <= CTDL_THREAD_STOP_REQ)
                {
                        syslog(LOG_DEBUG, "Thread %s (0x%08lx) refused stop request.\n", CT->name, CT->tid);
                        CT->state = CTDL_THREAD_RUNNING;
                }
                citthread_mutex_unlock(&CT->ThreadMutex);
        }

        ctdl_thread_internal_change_state(CT, CTDL_THREAD_RUNNING);

        return ret;
}



void *new_worker_thread(void *arg);
extern void close_masters (void);



void go_threading(void)
{
        int i;
        CtdlThreadNode *last_worker;

        /*
         * Initialise the thread system
         */
        ctdl_thread_internal_init();

        /* Second call to module init functions now that threading is up */
        initialise_modules(1);
        CtdlThreadCreate("select_on_master", CTDLTHREAD_BIGSTACK, select_on_master, NULL);

        /*
         * This thread is now used for garbage collection of other threads in the thread list
         */
        syslog(LOG_INFO, "Startup thread %ld becoming garbage collector,\n", (long) citthread_self());

        /*
         * We do a lot of locking and unlocking of the thread list in here.
         * We do this so that we can repeatedly release time for other threads
         * that may be waiting on the thread list.
         * We are a low priority thread so we can afford to do this
         */
        
        while (CtdlThreadGetCount())
        {
                if (CT->signal)
                        exit_signal = CT->signal;
                if (exit_signal)
                {
                        CtdlThreadStopAll();
                }
                check_sched_shutdown();
                if (CT->state > CTDL_THREAD_STOP_REQ)
                {
                        begin_critical_section(S_THREAD_LIST);
                        end_critical_section(S_THREAD_LIST);
                        
                        ctdl_thread_internal_check_scheduled(); /* start scheduled threads */
                }
                
                /* Reduce the size of the worker thread pool if necessary. */
                if ((CtdlThreadGetWorkers() > config.c_min_workers + 1) && (CtdlThreadWorkerAvg < 20) && (CT->state > CTDL_THREAD_STOP_REQ))
                {
                        /* Ask a worker thread to stop as we no longer need it */
                        begin_critical_section(S_THREAD_LIST);
                        last_worker = CtdlThreadList;
                        while (last_worker)
                        {
                                citthread_mutex_lock(&last_worker->ThreadMutex);
                                if (last_worker->flags & CTDLTHREAD_WORKER && (last_worker->state > CTDL_THREAD_STOPPING) && (last_worker->Context == NULL))
                                {
                                        citthread_mutex_unlock(&last_worker->ThreadMutex);
                                        break;
                                }
                                citthread_mutex_unlock(&last_worker->ThreadMutex);
                                last_worker = last_worker->next;
                        }
                        end_critical_section(S_THREAD_LIST);
                        if (last_worker)
                        {
#ifdef WITH_THREADLOG
                                syslog(LOG_DEBUG, "Thread system, stopping excess worker thread \"%s\" (0x%08lx).\n",
                                        last_worker->name,
                                        last_worker->tid
                                        );
#endif
                                CtdlThreadStop(last_worker);
                        }
                }
        
                /*
                 * If all our workers are working hard, start some more to help out
                 * with things
                 */
                /* FIXME: come up with a better way to dynamically alter the number of threads
                 * based on the system load
                 */
                if (    (((CtdlThreadGetWorkers() < config.c_max_workers)
                        && (CtdlThreadGetWorkerAvg() > 60))
                        || CtdlThreadGetWorkers() < config.c_min_workers)
                        && (CT->state > CTDL_THREAD_STOP_REQ)
                )
                {
                        /* Only start new threads if we are not going to overload the machine */
                        /* Temporarily set to 10 should be enough to make sure we don't stranglew the server
                         * at least until we make this a config option */
                        if (CtdlThreadGetLoadAvg() < ((double)10.00)) {
                                for (i=0; i<5 ; i++) {
                                        CtdlThreadCreate("Worker Thread",
                                                CTDLTHREAD_BIGSTACK + CTDLTHREAD_WORKER,
                                                worker_thread,
                                                NULL
                                                );
                                }
                        }
                        else
                                syslog(LOG_WARNING, "Server strangled due to machine load average too high.\n");
                }

                CtdlThreadGC();

                if (CtdlThreadGetCount() <= 1) // Shutting down clean up the garbage collector
                {
                        CtdlThreadGC();
                }
                
#ifdef THREADS_USESIGNALS
                if (CtdlThreadGetCount() && CT->state > CTDL_THREAD_STOP_REQ)
#else
                if (CtdlThreadGetCount())
#endif
                        CtdlThreadSleep(1);
        }
        /*
         * If the above loop exits we must be shutting down since we obviously have no threads
         */
        ctdl_thread_internal_cleanup();
}