multithreading, possible problems

[stmfc]

i have implemented famous producer consumer example for multi-threading tutorials, to have some insight about multi-threading.
there is producer thread which inserts into a buffer, if the buffer is not full.
if the buffer is full it waits.
there is a consumer thread which removes from the buffer, if the buffer is not empty. if the buffer is empty it waits.

although my implementation works succesfully, i am suspicious about my design,
it may cause dead locks:

here is the pseudo code:

thread_inserter:  
buffer.push();
inside push method:  if(storedItems>0)  notify();
inside push method:  if(storedItems==MAX_SIZE)   wait();  else insertData();
 
thread_remover:
buffer.pop():
inside pop method:  if(storedItems<MAX_SIZE)  notify();
inside pop method:  if(storedItems==0)  wait();  else removeData();
 

do you think that there is a problem with my locating both wait and notify methods in the same methods ?

[JosAH]

i have implemented famous producer consumer example for multi-threading tutorials, to have some insight about multi-threading.
there is producer thread which inserts into a buffer, if the buffer is not full.
if the buffer is full it waits.
there is a consumer thread which removes from the buffer, if the buffer is not empty. if the buffer is empty it waits.

although my implementation works succesfully, i am suspicious about my design,
it may cause dead locks:

here is the pseudo code:

thread_inserter:  
buffer.push();
inside push method:  if(storedItems>0)  notify();
inside push method:  if(storedItems==MAX_SIZE)   wait();  else insertData();
 
thread_remover:
buffer.pop():
inside pop method:  if(storedItems<MAX_SIZE)  notify();
inside pop method:  if(storedItems==0)  wait();  else removeData();
 

do you think that there is a problem with my locating both wait and notify methods in the same methods ?

Yup; the logic is not correct; read about the wait() call: it should be the body
of a while loop checking the condition. I hope you did synchronize on the buffer
which is the shared resource.

The producer should first wait on a full buffer, i.e. it shouldn't wait when another
item can be pushed into it. The consumeer should wait on an empty buffer, i.e.
it shouldn't wait when the buffer contains items. After the pushing (the producer)
and after the popping (the consumer) the waiting 'others' should be notified,
all of them.

kind regards,

Jos