On 12/18/06, Vlad Seryakov <[EMAIL PROTECTED]> wrote:
Still, even without the last free and with mutex around it, it core
dumps in free(gPtr) during the loop.
OK. Still doesn't mean your program is bug free :-)
There's a lot of extra stuff going on in your example program that
makes it hard to see what's going on. I simplified it to this:
#include <tcl.h>
#include <stdlib.h>
#include <assert.h>
#define MemAlloc ckalloc
#define MemFree ckfree
void *gPtr = NULL; /* Global pointer to memory. */
void
Thread(void *arg)
{
assert(gPtr != NULL);
MemFree(gPtr);
gPtr = NULL;
}
int
main (int argc, char **argv)
{
Tcl_ThreadId tid;
int i;
for (i = 0; i < 100000; ++i) {
gPtr = MemAlloc(1024);
assert(gPtr != NULL);
Tcl_CreateThread(&tid, Thread, NULL,
TCL_THREAD_STACK_DEFAULT, TCL_THREAD_JOINABLE);
Tcl_JoinThread(tid, NULL);
assert(gPtr == NULL);
}
}
Works for me.
I say you can allocate memory in one thread and free it in another.
Let me know what the bug turns out to be..!
Stephen Deasey wrote:
> On 12/18/06, Vlad Seryakov <[EMAIL PROTECTED]> wrote:
>> I tried to run this program, it crahses with all allocators on free when
>> it was allocated in other thread. zippy does it as well, i amnot sure
>> how Naviserver works then.
>
>
> I don't think allocate in one thread, free in another is an unusual
> strategy. Googling around I see a lot of people doing it. There must
> be some bugs in your program. Here's one:
>
> At the end of MemThread() gPtr is checked and freed, but the gMutex is
> not held. This thread may have finished it's tight loop, but the other
> 3 threads could still be running. Also, the gPtr is not set to NULL
> after the free(), leading to a double free when the next thread checks
> it.
>
>
>> #include <tcl.h>
>>
>> #define MemAlloc ckalloc
>> #define MemFree ckfree
>>
>> int nbuffer = 16384;
>> int nloops = 50000;
>> int nthreads = 4;
>>
>> int gAllocs = 0;
>> void *gPtr = NULL;
>> Tcl_Mutex gLock;
>>
>> void MemThread(void *arg)
>> {
>> int i,n;
>> void *ptr = NULL;
>>
>> for (i = 0; i < nloops; ++i) {
>> n = 1 + (int) (nbuffer * (rand() / (RAND_MAX + 1.0)));
>> if (ptr != NULL) {
>> MemFree(ptr);
>> }
>> ptr = MemAlloc(n);
>> // Testing inter-thread alloc/free
>> if (n % 5 == 0) {
>> Tcl_MutexLock(&gLock);
>> if (gPtr != NULL) {
>> MemFree(gPtr);
>> }
>> gPtr = MemAlloc(n);
>> gAllocs++;
>> Tcl_MutexUnlock(&gLock);
>> }
>> }
>> if (ptr != NULL) {
>> MemFree(ptr);
>> }
>> if (gPtr != NULL) {
>> MemFree(gPtr);
>> }
>> }
>>
>> void MemTime()
>> {
>> int i;
>> Tcl_ThreadId *tids;
>> tids = (Tcl_ThreadId *)malloc(sizeof(Tcl_ThreadId) * nthreads);
>>
>> for (i = 0; i < nthreads; ++i) {
>> Tcl_CreateThread( &tids[i], MemThread, NULL,
>> TCL_THREAD_STACK_DEFAULT, TCL_THREAD_JOINABLE);
>> }
>> for (i = 0; i < nthreads; ++i) {
>> Tcl_JoinThread(tids[i], NULL);
>> }
>> }
>>
>> int main (int argc, char **argv)
>> {
>> MemTime();
>> }
>
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--
Vlad Seryakov
571 262-8608 office
[EMAIL PROTECTED]
http://www.crystalballinc.com/vlad/
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