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imperfect_notes/pragy/operating systems 3.md
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@ -70,7 +70,7 @@ Critical Section
Use smaller atomic operation to create large, custom atomic operation Use smaller atomic operation to create large, custom atomic operation
![96915cd0.png](:storage/b4659e19-c2c4-4830-adf6-413c1cc30e92/be23bceb.png) ![96915cd0.png](attachments/be23bceb.png)
-- -- -- --
@ -100,7 +100,7 @@ Opposite - starvation
Peterson's Solution Peterson's Solution
------------------- -------------------
![6b9b2f89.png](:storage/b4659e19-c2c4-4830-adf6-413c1cc30e92/6b9b2f89.png) ![6b9b2f89.png](attachments/6b9b2f89.png)
- flag: tells the other guy to wait - flag: tells the other guy to wait
- turn: to prevent a deadlock where everyone is waiting. Ensures that atleast 1 is running CS. - turn: to prevent a deadlock where everyone is waiting. Ensures that atleast 1 is running CS.
@ -110,11 +110,11 @@ Peterson's Solution
MuteX MuteX
----- -----
![28b6ef71.png](:storage/b4659e19-c2c4-4830-adf6-413c1cc30e92/28b6ef71.png) ![28b6ef71.png](attachments/28b6ef71.png)
Note: aquiring and releasing locks is atomic Note: aquiring and releasing locks is atomic
![5407fbc7.png](:storage/b4659e19-c2c4-4830-adf6-413c1cc30e92/5407fbc7.png) ![5407fbc7.png](attachments/5407fbc7.png)
cons: busy wait - splinlocks cons: busy wait - splinlocks
pros: no context switch pros: no context switch
@ -125,9 +125,9 @@ Semaphores
- integer variables - integer variables
- wait and signal, both atomic, only 2 operations defined - wait and signal, both atomic, only 2 operations defined
![b824a258.png](:storage/b4659e19-c2c4-4830-adf6-413c1cc30e92/b824a258.png) ![b824a258.png](attachments/b824a258.png)
![301d7713.png](:storage/b4659e19-c2c4-4830-adf6-413c1cc30e92/301d7713.png) ![301d7713.png](attachments/301d7713.png)
Note that S++, S-- is atomic here Note that S++, S-- is atomic here
On single processors this can be implemented by disabling interrupts during the execution of wait and signal; Multiprocessor systems have to use more complex methods, including the use of spinlocking. On single processors this can be implemented by disabling interrupts during the execution of wait and signal; Multiprocessor systems have to use more complex methods, including the use of spinlocking.
@ -135,7 +135,7 @@ On single processors this can be implemented by disabling interrupts during the
Binary Semaphore -> Mutex Binary Semaphore -> Mutex
------------------------- -------------------------
![fb5970c7.png](:storage/b4659e19-c2c4-4830-adf6-413c1cc30e92/fb5970c7.png) ![fb5970c7.png](attachments/fb5970c7.png)
Counting Semaphore Counting Semaphore
------------------ ------------------
@ -148,7 +148,7 @@ Integer values
Resource Allocation graph & Deadlocks revisited Resource Allocation graph & Deadlocks revisited
----------------------------------------------- -----------------------------------------------
![3598cec9.png](:storage/b4659e19-c2c4-4830-adf6-413c1cc30e92/3598cec9.png) ![3598cec9.png](attachments/3598cec9.png)
Conditions Conditions
1. Mutual Exclusion 1. Mutual Exclusion
@ -157,7 +157,7 @@ Conditions
4. Circular Wait 4. Circular Wait
![02fe9460.png](:storage/b4659e19-c2c4-4830-adf6-413c1cc30e92/02fe9460.png) ![02fe9460.png](attachments/02fe9460.png)
no cycle = no deadlock no cycle = no deadlock
cycle and only one of each resource = deadlock cycle and only one of each resource = deadlock
@ -223,4 +223,4 @@ sem.release()
[Semaphore (Java Platform SE 7 )](https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/Semaphore.html) [Semaphore (Java Platform SE 7 )](https://docs.oracle.com/javase/7/docs/api/java/util/concurrent/Semaphore.html)
[Semaphores](http://tutorials.jenkov.com/java-concurrency/semaphores.html) [Semaphores](http://tutorials.jenkov.com/java-concurrency/semaphores.html)