Tightly Coupled Communicating System

Tightly Coupled Communicating System

Producer

Shared

Consumer

interpretation:

flag=0 means buffer is empty

therefore OK to proceed and produce new value

flag=1 means buffer is full

therefore must wait until contents have been used

flag = number

of valid data items

remaining in buffer

flag=0 means buffer is empty

therefore must wait for new contents

flag=1 means buffer is full

therefore OK to proceed and use contents

while (1)

{ ...

int ok=0;

while (!ok)

{ P(s);

if (flag==0)

ok=1;

V(s);

if (!ok)

sleep(1); }

...

generate new value;

...

P(s);

copy new value into buffer;

flag=1;

V(s);

... }

buffer: data area

flag: int

s: semaphore

while (1)

{ ...

int ok=0;

while (!ok)

{ P(s);

if (flag==1)

ok=1;

V(s);

if (!ok)

sleep(1); }

...

P(s);

copy new value from buffer;

flag=0;

V(s);

...

make use of new value;

... }

Loosely Coupled Communicating System

Producer

Shared

Consumer

QueueFront == NULL

means there is no data

ready for use at the moment.

while (1)

{ link *item=NULL;

...

generate new value;

...

item=new link();

item->data=the new value;

item->next=NULL;

P(s);

if (QueueFront==NULL)

QueueFront=item;

else

QueueBack->next=item;

QueueBack=item;

V(s);

... }

struct link

{ data: whatever;

next: ptr to link; };

QueueFront,

QueueBack: ptr to link;

s: semaphore

while (1)

{ link *item=NULL;

P(s);

if (QueueFront!=NULL)

{ item=QueueFront;

QueueFront=QueueFront->next; }

V(s);

...

if (item==NULL)

sleep(1);

else

{ new value = item->data;

make use of new value;

... }