Monica
💫 Summary
The video discusses the producer-consumer problem in operating systems, where two parallel processes share a common buffer for producing and consuming items. It explains the code for the producer and consumer, and demonstrates the issue of race condition, where wrong values are produced due to the order of execution.
✨ Highlights📊 Transcript
The producer-consumer problem involves two parallel processes, one producing an item and the other consuming it, with shared resources.
00:01
The producer produces an item and places it in a buffer.
The consumer consumes the item and executes its code.
Both processes share a buffer and a count variable.
The video explains the process of producing and placing items in a buffer in the producer-consumer problem.
03:55
When the buffer is full, the producer gets stuck in an infinite loop.
The position of the next empty slot in the buffer is determined by the "in" variable.
The "in" variable is incremented using the formula (in + 1) mod n, where n is the maximum size of the buffer.
The count variable is also incremented to keep track of the number of items in the buffer.
The section explains how the consumer works in the producer-consumer problem.
07:41
The consumer confirms from the same buffer before consuming an item.
If the buffer is empty (count == 0), the consumer gets stuck in an infinite loop.
The consumer takes out items from the buffer starting from position 0 and incrementing to the next position.
The buffer out position is initially 0 and the value is X1.
The video explains the execution of the instruction "count = count - 1" in the producer-consumer problem.
11:24
The instruction is executed through micro instructions.
The count value is loaded from memory and stored in a register.
The count value is decremented from 1 to 0, indicating that an item has been consumed.
The buffer is empty after the item is consumed.
The producer can continue producing items if there is space in the buffer.
The producer is ready to produce a new item and inserts it into the buffer at the next empty slot.
15:15
The producer inserts the item X4 into the buffer at the third position.
The value of "In" is incremented to indicate the next empty slot.
The count is updated to reflect the total number of items produced.
This section explains the execution sequence of the producer and consumer processes in the producer-consumer problem.
19:03
The CPU searches for new processes in the ready queue.
The consumer process executes the code while (count==0) and finds that there are items to be consumed.
The consumer consumes the item at position 0 in the buffer.
The out value is updated to 1.
The count value is decremented to 2.
The system gets preempted before executing the third instruction.
The video discusses the issue of race condition in the producer-consumer problem.
22:47
The consumer checks the values in the PCB and finds that all values have been executed except for the third one.
The value of count is updated from 4 to 2 in the memory location of count.
The count value does not match the number of items in the buffer, indicating a race condition problem.
00:01Producer consumer problem...
00:02Producer consumer problem is a standard problem of multi process synchronization
00:07Means we've two processes here, one is of producer and one is of consumer
00:13And the assumption is both processes are coming at a same time,
00:16means both are parallel processes And they're sharing something
00:20Means we are talking about cooperative processes,
00:23In cooperative processes, two or more processes... They share something,
00:28it could be code or resources, or memory or some variable also
00:34Something common between them, so we are talking about the cooperative processes only
00:38So one is producer and other one is consumer
00:41This is the code for the consumer and this is the code for the producer
00:45It's just a code written in normal C language
00:48Let's see producer, when producer's code runs then producer produces an Item
00:56And places it in a buffer
00:58And what consumer do is, it consumes the item and to consume it'll execute this whole code
01:04And then finally will bring out the item from the buffer
01:08And then it can process anything it wants
01:11This is the way of how we are doing this
01:14So let's start with the case 1, we are starting with the normal case i.e. best case,
01:21because when we run the program then there could be many cases
01:26I mean when we execute a program in the real world or creates some situation in the real world
01:33then we are not bound with only one or two cases
01:36I have to check all cases, so we are taking a simple case
01:41Like Case1... In case one, producer is producing an item
01:45It's just any random item let's say item is X1
01:49Item name is X1
01:51Now... to producer item X1, producer's process will execute this code
01:57So it's simple... Int count = 0 Count is a global variable that both are sharing
02:04We just talked that there's some share or something common in cooperative
02:09Here in producer consumer problem, this is the buffer which is shared by both the processes
02:15Both processes are sharing this buffer
02:18Buffer is like a memory or space in RAM that both processes are sharing
02:24And one more thing they are sharing is the count variable
02:27Now void producer (void).... Int item p this is the local variable of producer
02:34While (true), which is always true
02:36produce item (item p)... this is a function which will produce an item
02:40So let's say Item P... while (count == n)
02:44n is the size of the buffer I've already picked up n's size as 8
02:49Means the size of buffer is 8 And index is zero to n-1
02:54Means from zero to 8-1 i.e. 7
02:58so already there's numbering, 0,1, 2, 3,... 5, 6 ,7
03:01And we are doing increment and decrement by using two local variables
03:08Consumer uses out,
03:14And producer uses In
03:20Now let's say that producer produced an item while (count == n)
03:25What is the meaning of this condition if the count is ==n
03:30Means if the size of count is equal to size of the buffer, it means that the buffer has over flown
03:37If buffer is overflowing, means I can't produce any other item in it
03:42So if I can't do it, then there's a semicolon there
03:47Means this code will stop here definitely Means this producer will get stuck in infinite loop
03:55obviously if my buffer is filled from 0 to 8 completely
04:02Now if counts value is equal to the maximum size of buffer
04:07This is the condition for buffer full Buffer is full
04:13obviously if the buffer is overflow then we can't produce any item
04:18even if I created an item then where will I save it?
04:21Then I have to put it in the buffer but buffer is already full
04:25then here producer will get stuck in infinite loop
04:29But we are taking the normal case where let's say my buffer is initially empty
04:35and producer came and want to produce a new item
04:38So now let's jump to the next line... Item p Buffer [in]
04:43Means whatever the item... Let's say Item is X1 Buffer [in]... by default in
04:52Starting position of in is 0 in tell the address of next empty slot
04:58Means it tell the addresses of empty slot where that item will reside inside the buffer
05:05So now my item is pointing out at int 0 position Means 0th position is empty
05:11Means we are incrementing like this
05:15When item will keep coming then we'll keep incrementing in
05:19And when we'll release item then we'll increment out
05:24Let's say Item P i.e. X1... and buffer in what is the position of in?... Zero
05:31So we filled item X1 in the buffer
05:36we filled item X1 in the buffer in =( in+1) mod n
05:41What is the value of in?... Zero then (0+1) mod 8
05:50n is the maximum size of the buffer i.e. 8 so this 1 mod 8
05:56and we already know this is the reminder 1 mod 8 is equal to 1...
06:00means now in will become increment to 1
06:05so this is a simple case that how we produced an item and placed it in the buffer
06:11now the last condition is count = count +1
06:15Now count variable which is used by both producer and consumer
06:21So I have to increment count variable also
06:25count variable which is initially zero Count says that how many items are there in the buffer
06:30for now there's no item so it's a zero But we added a new item i.e. X1
06:36so count will also change from zero to 1
06:40so this is how the code will execute
06:43now if you see this part
06:47Count = count +1 this is an important part over there
06:51count is a simple instruction This is a simple instruction of C, count = count + 1
06:57but how CPU executes it... this is very important
07:01CPU converts every instruction into micro instruction and then executes it
07:07so how this instruction will convert into micro instruction?
07:12first we'll load count's value from the memory in a register... Let's say register is Rp
07:20Because CPU works on registers first for efficiency and time saving
07:26so what I did? count's value was Zero initially
07:31So I loaded zero in the register
07:36Then increment... INCR is increment Increment of Rp
07:41so Rp's value will change from zero to 1 in the register
07:45and then we store the value of Rp into m [count]
07:49so M [count] will change from 0 to 1
07:53Same..
07:54Let's say how the consumer works
07:58Now whenever consumer wants to consume an item
08:02then it'll confirm from the same buffer Means it'll use the same buffer
08:07means both are sharing the common buffer over there
08:10now they are sharing the common buffer then let's say consumer came and chose item C
08:16This is the while (true) which is always true while (count ==0)
08:21What is the meaning of while (count ==0)? It means if count's value is equal to zero...
08:26count tells how many items are there in the buffer
08:30and if there's no item in the buffer Means my buffer is totally empty
08:36so obviously this will be an infinite loop means consumer don't have anything to consume
08:43so it'll get stuck here in the infinite loop so what this condition is telling us?... Buffer empty
08:53that the buffer is empty... if buffer is empty then there's nothing to consume from the buffer
09:02so consumer's code will stuck in infinite loop
09:06so let's say that there's something always to consume so Item C... Buffer (out)
09:12Now out is what?... out is by default again it's starting from the zero
09:18Means how we are running the items when putting the item then we are putting from 0 to 7
09:25and when we are bringing out items then we'll keep incrementing to next position from 0
09:31and now we are using mod then what is the advantages of mod??
09:34it'll move from 7th position back to 0th position
09:40Let's say buffer out... what is buffer out, out value is initially 0,
09:45because we're always putting out item at 0th position
09:49We are entering item at 0th position and taking out at 0th position also
09:55So let's say buffer out... what is the position of buffer out?... Zero
10:01so whatever value is there in the 0th position, it'll come in the item C
10:05what's the value in this?... X1
10:08There's an item X1 which is primarily produced by producer
10:12so X1 item will come under item C,
10:16now when X1 item will come in item C, then we have to update out
10:21because out will show at the next value
10:24because consumer have already consumed it, so we'll increment out from zero to one
10:32so that consumer have to consume a new item
10:36so it's fine it can consume item from 1 position also
10:39In any case, it maybe possible that my buffer is filled,
10:43then consumer can pick multiple items also one by one
10:49We changed out's value from 0 to 1
10:51now it'll point on 1, if there'll some item then it'll consume from there
10:55then it'll keep moving next, this is the way so out = (out +1) mod n
11:00so out's value in starting is 0, so (0+1) mod n
11:07What is mod n?... n value's 8 so 1 mod 8... i.e. . So out value will be out
11:16so I updated out's value from 0 to 1
11:19now this is again important because count is common in both
11:24Count variable is common in both that's why this is the most important instruction
11:31Count = count - 1 Count -1 means...
11:35we consumed an item, then obviously we have to reduce count's value by 1
11:41so count = count - 1 this is also a normal instruction
11:46We've written a line in C count = count -1
11:49But How does CPU executes it?... again through micro instructions
11:54Let's say what it'll do first? count value from memory...
11:57What is the count value now?... count value is 1
12:01because there was just one value in buffer We entered that one value, so count value is one
12:08so 1 will be loading into the register let's say there's a dedicated register for consumer
12:17so value 1 will get load in that consumer's register
12:20Decrement of Rc... means we decremented value from 1 to 0
12:24and then zero will be loaded into n count
12:28means we again changed count's value from 1 o 0, means stored value from 1 to 0
12:36So it means count's value now is also zero
12:39so count's value zero means that we consumed the item from here
12:45so there's no item which is left over there
12:50obviously there's no item, we saw a simple case, first we produced an item, then placed it in buffer
12:58then consumer consumed the item took out of the buffer
13:02then count changed again from 0 to 1, and then from 1 to 0
13:06we took out the X1 that we produced
13:10now out will point on next one that it wants to read
13:16and if there's next item then it'll use it
13:19In is also there... if I want to produce some item then we'll produce it here
13:27this way we'll keep incrementing when we'll go from 7 to 8
13:31then 8 mod 8... again 0 then again my pointer will move after 7 to 0
13:37This is a normal case, which we generally call best case
13:41that if my code will work in a way that producer came first,
13:46then consumer came, then producer came and again consumer
13:48then there's no problem
13:50this will be perfectly fine, but now we are moving towards the next
13:56Next case is...
14:02Let's say... now we are talking about process synchronization
14:08in process synchronization if these processes aren't synchronized
14:27Let's say... at any point of time producer produced three items
14:36Let's say X1... X2, ... X3
14:40These three items at any point of time, anytime.. this can happen this is one of the case
14:45these three items have been produced so in count it's showing 3
14:49Because there's three items so value in count is 3
14:55In... what In will show here? Always the next empty slot
15:01As we discussed... Next empty slot
15:03because we always keep In's value one extra incremented
15:08so that we can keep getting next value where I have to place the item
15:15and out.... Let's say, that consumer haven't consumed any item until now
15:22so we are starting from zero
15:24Now let's run this program again,
15:28let's say producer is ready to produce one more item
15:33Producer has already produced three items and now wants to produce a new item
15:37so we are running this code again
15:39Let's say producer produced an item while count is == 1
15:46While (count ==n) Count value is 3
15:503==n? NO... false, because still we have empty slots
15:55so we'll easily jump from here to next
15:57Means we came out of the loop
15:59Buffer... Let's say the item is X4
16:06In this case, Let's say the item is X4
16:09So we'll do In X4... What is the In position?... 4
16:134 position is what??...
16:18This is 3... because next empty position is three
16:21So let's say, we'll insert the item in third position
16:26This is the third position... So X4, we inserted X4 here
16:31This statement says X4 will be inserted into buffer in
16:36What is the In value?... 3
16:38So in buffer IN, we inserted an item X4 in 3 value at 3rd place
16:47In = In + 1... Again we incremented In Because In always tells the next empty slot
16:55so that producer can produce next empty slot there
16:59Now let's say count = count + 1 Because we have to increment count
17:04Because now here 4 items came but count is at 3
17:10so obviously we've to update count so my whole producer's code will terminate
17:17But let's say count = count + 1
17:20This one... load Rp, m [ count ] What's the count value now?
17:26Count value is three... Previously count value is 3
17:32Three value will be loaded into the Rp
17:37Let's say there's one register Rp in which we loaded value 3
17:45Now, Increment of Rp... Next section is increment of Rp
17:49Means we incremented Rp form 3-4 When incremented from 3 to 4...
17:56Let's say third instruction is store Rp into m [ load ]
18:00But now we are taking one case that after this 2nd instruction this producer got pre-empted
18:11Means this process has got pre-empted because whenever we run processes in real time
18:17Then process can get pre-empt anytime, reason could be... Interrupt
18:23Maybe some hardware of software got interrupt or some high priority process arrived
18:29or time quantum... that maybe its time quantum got expired
18:34In any case, process can get pre-empt anytime
18:37So let's say it executed 1 & 2 instruction it executed this 1st & 2nd one
18:46entered the value of m [count] i,e, 3 in the Rp Did increment of Rp, it became from 3 to 4
18:52Internal resistor value changed from 3 to 4
18:55But before it would run 3rd instruction, the producer code got pre-empted already
19:03CPU will always search for new processes,
19:06if there's any other process in the ready queue that it can change to running
19:10yes, there's one more process
19:13Now see, consumer came and run this code... while (count==0)
19:19we have already a lot of items to be consumed, so this is false
19:24so it came in, buffer out... what is out value?... Out value is Zero
19:29means we can read something with zero value here...
19:32What is value at 0th position?.... X1
19:35So it'll put X1 in item C... will consume it Out = (out+1 ) mod n
19:41The same....out value is zero 0+1 mod 8 i.e. 1
19:46so we shifted value from zero to one here and item x1 got consumed from here
19:54obviously when it placed item in its local variable then item left the buffer
20:01We did out = out +1 Count = count -1
20:05The next instruction is count = count -1
20:09m [count]... same What is the m [count] over there
20:12m [ count] is 3... count value is 3
20:16it entered count value 3 in the register Let's take a register here... Rc
20:24In Rc register we entered value i.e. 3,
20:30count's value is 3 because it didn't get updated until now and system already got pre-empted
20:36so my count value here came 3... decrement of Rc i.e. 2
20:43It got decremented... but same Before I would execute third instruction,
20:47system got pre-empted already before it
20:50let me write here for your easiness... Case: In this case what we are doing
20:55First of all producer came... producer is executing the instruction I & II
21:06This instruction I & II
21:10But before it would execute instruction III, consumer already arrived
21:17This is how we are doing it first producer came, executed item 1 and instruction 2
21:23after that, consumer arrived consumer executed instruction 1 and instruction 2
21:29This is instruction I & II...
21:32but before it would execute III, it got pre-empted and producer came again
21:43When producer came again, then it has already executed up to here
21:49So this value will be same in the PCB that we have the process executed up to here
21:55So we'll resume it, we'll never restart it otherwise our CPU's efficiency will get so much reduced
22:02So PCB will indicate that we've done up to here Only third instruction was left
22:06So we executed third information that's i3
22:10The moment we executed i3, what is the value of Rp?... 4
22:16Value of Rp is 4 in the local register So we loaded 4 value in the count
22:26Now the count is updated with 4
22:30Count is updated with 4 means third instruction got executed
22:35Code got terminated because this process has ended
22:39So when it got over then it got terminated
22:42when it got terminated then the consumer will get the control back
22:47so in consumer also we'll check in PCB, all these values were executed already
22:53In count also, this one and two was already done Just third one was left
22:57So which is the third one again?... consumer's i3
23:03This is the flow...
23:09which will help you how to execute this
23:14So consumer came and run the last instruction i.e. i3 The moment it ran i3
23:21What is Rc... In Rc the value in register is 2 We'll load 2 value... memory count
23:29Memory location of count... What is memory location of count?... This
23:33So we again updated the value from 4 to 2 Now the value of count is 2
23:39What is the meaning of that?
23:42here this statement got executed, means this code is also executed,
23:46when this code got executed then this also got terminate
23:50so when both process got terminated... Now value of count is 2
23:56So it means I have 2 items in the buffer But just check the buffer...
24:03How many items are there in the buffer 1... 2.... 3
24:07there are 3 items in the buffer But the count is wrong over there
24:14And obviously it should be 3...
24:15we had 3 items, out of them, 1 we produced and then consumed one
24:21so it became 4 and should be 3 back again but here count says that there are 2 values only
24:28But there are 3...
24:31So there are 3 values in buffer and count says 2, so this is the problem
24:36This is again race condition problem We checked it out in the last video also
24:40This is again called the race condition where wrong values are competing
24:46if we ran producer here first,
24:48if you'll run consumer first then producer then there must be something else value
24:53But three value won't arrive so this is the case because of which
24:57we failed to achieve process synchronization so here we are getting wrong value
25:03So you just focus on producer, then i1, i2 of producer then consumer i1, i2 of consumer
25:13then again producer... just make a note of that
25:20If you have any doubt in middle then you can revive the video and play it again
25:25This is the flow that how we deal with the producer- consumer problem
25:31Now some of the viewers might be thinking that why this case has been made
25:38Because I said already that when we bring a situation in real world
25:43even if we brings a software in the market, so when we do its testing
25:47then we don't see 3-4 cases in testing
25:50we tries to get maximum situations to test the case, that's the best
25:55so there could be a lot of cases to execute this
25:59but does processes are getting synchronize in all cases?... NO
26:05So there's one case if we'll execute it like this in this way... here problem will create
26:14So this is the problem count is telling 2, but right one is 3
26:18so this is again the problem, if the process synchronization is not done then this problem can arise
26:24now we can remove it again using the binary semaphore, using monitors,
26:28using locks and other methods are there, which we'll see in the future videos
26:33Thank You guys!!
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FAQs about This YouTube Video

1. What is the producer-consumer problem in operating systems?

The producer-consumer problem in operating systems involves two parallel processes that share a common buffer. The producer produces items and places them in the buffer, while the consumer consumes the items from the buffer. However, there is a race condition issue where the count variable does not accurately reflect the number of items in the buffer, leading to synchronization problems.

2. How does the producer-consumer problem impact synchronization in operating systems?

The producer-consumer problem impacts synchronization in operating systems by causing race condition issues. These issues occur when the count variable does not accurately reflect the number of items in the buffer, leading to synchronization problems between the producer and consumer processes.

3. What are the challenges posed by the producer-consumer problem in operating systems?

The challenges posed by the producer-consumer problem in operating systems include synchronization issues, race conditions, and inaccuracies in the count variable. These challenges can lead to inefficiencies and errors in the producer-consumer process.

4. How can race conditions be addressed in the producer-consumer problem?

Race conditions in the producer-consumer problem can be addressed through various synchronization techniques such as mutex, semaphore, or conditional variables. These techniques help in coordinating the access to the shared buffer and preventing the count variable from becoming inaccurate.

5. What are the solutions to the synchronization problems caused by the producer-consumer problem?

The synchronization problems caused by the producer-consumer problem can be addressed by implementing synchronization mechanisms like mutex and semaphores. These mechanisms help in ensuring that the producer and consumer processes access the shared buffer in a coordinated manner, thus preventing synchronization problems.

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