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L19: Monitors (I)
Este texto se distribuye bajo los terminos de la Creative Commons License
Cesar Sanchez
Grado en Ingenierıa InformaticaGrado en Matematicas e Informatica
Universidad Politecnica de Madrid
Wed, 22-April-2015
Underco
nstructi
on! Donot prin
t
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HW9: Multibuffer con Monitores
Homework:HW1: Creacion de threads en JavaHW2: Provocar una condicion de carreraHW3: Garanatizar la exclusion mutua con espera activaHW4: Garantizar la exlusion mutua con semaforosHW5: Almacen de un dato con semaforosHW6: Almacen de varios datos con semaforosHW7: Especificacion de un recurso compartidoHW8: Multibuffer con metodos synchronizedHW9: Multibuffer con “Monitores”
Fecha de Cierre:Lunes 27-Abril-2015 23:59
Entrega online:http://lml.ls.fi.upm.es/~entrega
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HW9: Multibuffer con Monitores
3
HW9: Multibuffer con Monitores
Use cclib.Do not use Java locks&conditions!
4
Conditional Synchronization (with synchronize/notify())
hayDato?
Almacen1
getput(x)
d
prod1
prod2
prod3
cons1
cons2
cons3
example: producer consumer
4
Conditional Synchronization (with synchronize/notify())
hayDato?
Almacen1
getput(x)
d
prod1
prod2
prod3
cons1
cons2
cons3
example: producer consumer
ready queue
wait set
4
Conditional Synchronization (with synchronize/notify())
hayDato?
Almacen1
getput(x)
d
prod1
prod2
prod3
cons1
cons2
cons3
example: producer consumer
= F
alm(7)
alm(2)
4
Conditional Synchronization (with synchronize/notify())
hayDato?
Almacen1
getput(x)
d
example: producer consumer
prod2
cons1
cons2
cons3prod1
prod3
4
Conditional Synchronization (with synchronize/notify())
hayDato?
Almacen1
getput(x)
d
example: producer consumer
prod2
cons1
cons2
cons3prod1
prod3
4
Conditional Synchronization (with synchronize/notify())
hayDato?
Almacen1
getput(x)
d
example: producer consumer
cons1
prod2 cons2
cons3prod1
prod3
4
Conditional Synchronization (with synchronize/notify())
hayDato?
Almacen1
getput(x)
d
example: producer consumer
prod2 cons2
cons3
prod3 cons1
prod1
= T
= 7
CPRE for prod3 is false!
prod2
prod1
4
Conditional Synchronization (with synchronize/notify())
hayDato?
Almacen1
getput(x)
d
example: producer consumer
prod2
prod1
prod2
prod1
cons2
cons3
= T
= 7
prod3cons1
4
Conditional Synchronization (with synchronize/notify())
hayDato?
Almacen1
getput(x)
d
example: producer consumer
prod2
prod1
prod2
prod1
cons2
cons3
prod3
= T
= 7cons1
4
Conditional Synchronization (with synchronize/notify())
hayDato?
Almacen1
getput(x)
d
example: producer consumer
cons2
cons3
cons1
prod3wait-set
prod2
prod1
prod2
prod1
recheck CPRE
= F
4
Conditional Synchronization (with synchronize/notify())
hayDato?
Almacen1
getput(x)
d
example: producer consumer
prod2
prod1
prod2
prod1
cons2
cons3
cons1
prod3
= F
4
Conditional Synchronization (with synchronize/notify())
hayDato?
Almacen1
getput(x)
d
example: producer consumer
prod3
prod2
prod1
prod2
prod1
cons2
cons3
cons1
4
Conditional Synchronization (with synchronize/notify())
hayDato?
Almacen1
getput(x)
d
prod1
prod2
prod3
cons1
cons2
cons3
example: producer consumer
= T
= 3
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Problems with synchronize/notify()
hayDato?
Almacen1
getput(x)
d
prod1
prod2
prod3
cons1
cons2
cons3
= T
= 3
notify() does not guarantee which thread to wake-up
notifyAll() wakes up all threads
The ready queue is not (necessarily) FIFO PROBLEMS:InefficientStarvation
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Monitors
GOAL: Implement resources with Monitors
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Monitors
GOAL: Implement resources with Monitors
One wait-set
Non-deterministic
Java synchronized
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Monitors
GOAL: Implement resources with Monitors
One wait-set Several (associated) wait-sets
Non-deterministic FIFO queues
Java synchronized Monitors
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Monitors (1. Mutual exclusion)
To import the monitors from cclib:
import es.upm.babel.cclib.Monitor;
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Monitors (1. Mutual exclusion)
To create a monitor:
// data members:
Monitor mutex;
// constructor:
mutex = new Monitor();
Monitors are objects.
To import the monitors from cclib:
import es.upm.babel.cclib.Monitor;
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Monitors (1. Mutual exclusion)
To create a monitor:
// data members:
Monitor mutex;
// constructor:
mutex = new Monitor();
Monitors are objects.
To import the monitors from cclib:
import es.upm.babel.cclib.Monitor;
To use the monitor:
public Producto extraer() {
mutex.enter();
//...
mutex.leave();
return result;
}
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Monitors (1. Mutual exclusion)
To create a monitor:
// data members:
Monitor mutex;
// constructor:
mutex = new Monitor();
Monitors are objects.
To import the monitors from cclib:
import es.upm.babel.cclib.Monitor;
To use the monitor:
public Producto extraer() {
mutex.enter();
//...
mutex.leave();
return result;
}
hayDato?
Almacen1
getput(x)
d
= T
= 3
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Monitors (1. Mutual exclusion)
To create a monitor:
// data members:
Monitor mutex;
// constructor:
mutex = new Monitor();
Monitors are objects.
To import the monitors from cclib:
import es.upm.babel.cclib.Monitor;
To use the monitor:
public Producto extraer() {
mutex.enter();
//...
mutex.leave();
return result;
}
hayDato?
Almacen1
getput(x)
d
= T
= 3 mutex
ready queue (FIFO)
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Monitors (2. Conditional Synchronization)
Conditions are also objects!
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Monitors (2. Conditional Synchronization)
Conditions are also objects!
Each Condition has its own FIFO wait-set.
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Monitors (2. Conditional Synchronization)
To create a condition:
// data members:
Monitor.Cond cAlmacenar;
Monitor.Cond cExtraer;
// constructor:
cAlmacenar = mutex.newCond();
cExtraer = mutex.newCond();
Conditions are also objects!
To use the condition:
//...
cExtraer.await();
//...
cExtraer.signal();
//...
Each Condition has its own FIFO wait-set.
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Monitors (2. Conditional Synchronization)
To create a condition:
// data members:
Monitor.Cond cAlmacenar;
Monitor.Cond cExtraer;
// constructor:
cAlmacenar = mutex.newCond();
cExtraer = mutex.newCond();
Conditions are also objects!
To use the condition:
//...
cExtraer.await();
//...
cExtraer.signal();
//...
Each Condition has its own FIFO wait-set.
hayDato?
Almacen1
getput(x)
d
= T
= 3 mutex
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Monitors (2. Conditional Synchronization)
To create a condition:
// data members:
Monitor.Cond cAlmacenar;
Monitor.Cond cExtraer;
// constructor:
cAlmacenar = mutex.newCond();
cExtraer = mutex.newCond();
Conditions are also objects!
To use the condition:
//...
cExtraer.await();
//...
cExtraer.signal();
//...
Each Condition has its own FIFO wait-set.
hayDato?
Almacen1
getput(x)
d
= T
= 3 mutex
cExtraer (FIFO)
cAlmacenar (FIFO)
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Signaling Policies
There are different posible guarantees aboutwhich thread continues running after a signal()
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Signaling Policies
Signal & Continue (SC) : The process who signal keep the mutual exclusionand the signaled will be awaken but need to acquire the mutual exclusionbefore going.
There are different posible guarantees aboutwhich thread continues running after a signal()
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Signaling Policies
Signal & Continue (SC) : The process who signal keep the mutual exclusionand the signaled will be awaken but need to acquire the mutual exclusionbefore going.
Signal & Wait (SW) : The signaler is blocked and must wait for mutualexclusion to continue and the signaled thread is directly awaken and canstart continue its operations.
There are different posible guarantees aboutwhich thread continues running after a signal()
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Signaling Policies
Signal & Continue (SC) : The process who signal keep the mutual exclusionand the signaled will be awaken but need to acquire the mutual exclusionbefore going.
Signal & Wait (SW) : The signaler is blocked and must wait for mutualexclusion to continue and the signaled thread is directly awaken and canstart continue its operations.
Signal & Urgent Wait (SU) : Like SW but the signaler thread has theguarantee than it would go just after the signaled thread
There are different posible guarantees aboutwhich thread continues running after a signal()
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Signaling Policies
Signal & Continue (SC) : The process who signal keep the mutual exclusionand the signaled will be awaken but need to acquire the mutual exclusionbefore going.
Signal & Wait (SW) : The signaler is blocked and must wait for mutualexclusion to continue and the signaled thread is directly awaken and canstart continue its operations.
Signal & Urgent Wait (SU) : Like SW but the signaler thread has theguarantee than it would go just after the signaled thread
Signal & Exit (SX) : The signaler exits from the method directly after thesignal and the signaled thread can start directly.
There are different posible guarantees aboutwhich thread continues running after a signal()
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Signaling Policies
Signal & Continue (SC) : The process who signal keep the mutual exclusionand the signaled will be awaken but need to acquire the mutual exclusionbefore going.
Signal & Wait (SW) : The signaler is blocked and must wait for mutualexclusion to continue and the signaled thread is directly awaken and canstart continue its operations.
Signal & Urgent Wait (SU) : Like SW but the signaler thread has theguarantee than it would go just after the signaled thread
Signal & Exit (SX) : The signaler exits from the method directly after thesignal and the signaled thread can start directly.
There are different posible guarantees aboutwhich thread continues running after a signal()
cclib: SC + signaled thread becomes the first in the ready queue
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Monitors: summary
Syntax:
class Monitor
enter();
leave();
newCond();
class Monitor.Cond
await();
signal();
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Monitors: summary
Syntax:
class Monitor
enter();
leave();
newCond();
class Monitor.Cond
await();
signal();
Semantics:• enter(): grabs the monitor lock• leave(): returns the monitor lock• newCond(): creates a condition associated with the monitor• await(): puts thread to sleep in the wait-set of the condition and frees
the lock of the monitor• signal(): awakes the oldest thread in the wait-set and puts it first in
the ready queue
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Almacen1Monitor.java: almacenar()
public void almacenar(Producto producto) {
// access protocol
mutex.enter();
// CPRE:
if (hayDato) {
cAlmacenar.await();
}
// INV: !hayDato
// Critical Section
almacenado = producto;
hayDato = true;
// End critical section
// synchronization code for extraer() CPRE
cExtraer.signal();
mutex.leave();
}
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Almacen1Monitor.java: extraer()
public Producto extraer() {
Producto result;
// Access protocol
mutex.enter();
// CPRE
if (!hayDato) {
cExtraer.await();
}
// INV: hayDato
// Critical Section
result = almacenado;
almacenado = null;
hayDato = false;
// End critical section
// code for almacenar() CPRE
cAlmacenar.signal();
mutex.leave();
return result;
}
