The document discusses threads at the kernel and user level. It describes threads as the basic unit of CPU utilization consisting of a program counter, register set, and stack space. Threads share code, data, and operating system resources with other threads in a process. The document compares single-threaded and multi-threaded processes and models including one-to-one, many-to-one, and many-to-many. It provides details on thread support in Solaris 2, including lightweight processes (LWPs), and basic thread management.

1. Hilos
Capítulo 5
Silberschatz Galvin

2. Hilos2
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Hilos
Concepto
Beneficios
Hilos a nivel kérnel y a nivel usuario
Modelos multihilos
Hilos de Solaris 2
Hilos de Java

3. Hilos3
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Hilos
Un hilo (o proceso ligero) es una unidad básica de utilización
del CPU; consiste de:
• Contador de programa
• Conjunto de registros
• Espacio de stack

4. Hilos4
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Hilos
Un hilo comparte con sus hilos pares:
• Sección de código
• Sección de datos
• Recursos del sistema operativo
• En conjunto se les conoce como tarea
Un proceso tradicional o pesado, es igual a una tarea con un
hilo.

5. Hilos5
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un proceso
un hilo
varios procesos
un hilo por proceso
varios procesos
varios hilos por proceso
un proceso
varios hilos
Hilos y procesos

6. Hilos6
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Código Datos Archivos Código Datos Archivos
Hilo Hilos
Mono-hilo Multi-hilo
Procesos con un solo hilo y con múltiples
hilos

7. Hilos7
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Bloque de
control
del hilo
Stack
del
usuario
Stack
del
usuario
Stack
del
kernel
Stack
del
Kernel
Espacio de
direcciones
del usuario
Espacio de
direcciones
del usuario
Bloque de
control del
proceso
Bloque
de control
del proceso
Hilo
Modelo de proceso
de un solo hilo
Modelo de proceso
multihilos
Bloque de
control
del hilo
Stack
del
usuario
Stack
del
kernel
Hilo
Bloque de
control
del hilo
Stack
del
usuario
Stack
del
kernel
Hilo
Modelos de procesos de un solo hilo y de
muchos hilos

8. Hilos8
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Multihilo
Sistema operativo que mantiene varios hilos de ejecución
dentro de un mismo proceso.
MS-DOS soporta un solo hilo.
UNIX soporta múltiples procesos de usuarios, pero sólo un hilo
por proceso.
Windows 2000, Solaris, Linux, Mac OS, OS/2 soportan múltiples
hilos.

9. Hilos9
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Hilos
En una tarea donde hay múltiples hilos, mientras un hilo
servidor está bloqueado y esperando, otro hilo en la misma
tarea puede ejecutarse.
• Cooperación de múltiples hilos en la misma tarea aumenta la
tasa de trabajos por unidad tiempo y mejora el rendimiento.
• Aplicaciones que requieren compartir un buffer común
(productor-consumidor) sacan provecho de la utilización de
hilos.

10. Hilos10
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Hilos
Los hilos proveen un mecanismo que permiten a procesos
secuenciales hacer llamadas bloqueantes mientras otros en
paralelo ejecutan otras operaciones.

11. Hilos11
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Beneficios
Compartición de recursos
Economía
Utilización de arquitecturas de múltiples procesadores

12. Hilos12
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Hilos a nivel usuario
El manejo de los hilos lo hace una librería de hilos a nivel
usuario
Ejemplos
- Hilos POSIX
- Mach C-threads
- Hilos de Solaris

13. Hilos13
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Hilos a nivel usuario (un CPU con dos
núcleos)
Nivel kérnel
(sistema
operativo)
Nivel usuario
Proceso de usuario gestiona y
planifica los múltiples hilos
Core CoreCPU
Hardware
Planificador del SO

14. Hilos14
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Ventajas de los hilos a nivel usuario
Los hilos podían implementarse en las aplicaciones que se
ejecutaban en sistemas operativos que no son capaces de
planificar hilos
• Ejemplo: Primeras implementaciones de UNIX

15. Hilos15
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Desventajas de los hilos a nivel usuario
El planificador del sistema operativo solo ve un hilo por proceso
 No ve los hilos a nivel usuario
 Usa un solo núcleo del procesador en un procesador que tiene
más de un núcleo
 No puede distribuir los hilos a nivel el usuario en los dos
núcleos

16. Hilos16
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Hilos a nivel kérnel
Soportados por el kérnel
Ejemplos
• Windows 95/98/NT
• Solaris
• Linux
• Mac OS

17. Hilos17
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Hilos a nivel kernel (con un CPU con un solo
núcleo)
Nivel kérnel
(sistema
operativo)
Nivel usuario
CoreCPU
Hardware
Planificador del SO

18. Hilos18
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Hilos a nivel kernel (con un CPU con doble
núcleo)
Nivel kérnel
(sistema
operativo)
Nivel usuario
Core CoreCPU
Hardware
Planificador del SO

19. Hilos19
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Ventajas de los hilos a nivel kérnel
El proceso de usuario no se tiene que encargar de la
planificación de los hilos
Si tenemos un procesador con más de un núcelo, el Sistema
operativo puede planificar los hilos en diferentes núcleos

20. Hilos20
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Modelos multihilos
Muchos a uno
Uno a uno
Muchos a muchos

21. Hilos21
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Muchos a uno
Muchos hilos a nivel usuario mapeados a un hilo a nivel kérnel.
Usado en sistemas que no soportan hilos a nivel kérnel.

22. Hilos22
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Modelo muchos a uno
kk

23. Hilos23
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EjecuciónListo
Listo
Relaciones entre estados de ULTs y estados
de procesos
Ejecución
Bloqueado
Bloqueado
Listo Ejecución
Bloqueado
Hilo 1
Hilo 2
Proceso B
Kernel
Usuario

24. Hilos24
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Uno a uno
Cada hilo a nivel usuario corresponde a un hilo del kérnel.
Ejemplos:
- Windows 95/98/NT
- OS/2

25. Hilos25
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Modelo uno a uno
kk kk kk kk
Hilo a nivel usuario
Hilo a nivel kérnel

26. Hilos26
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Modelo muchos a muchos
kk kkkk
Hilo a nivel usuario
Hilo a nivel kérnel

27. Hilos27
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Soporte de hilos en Solaris 2
Solaris 2 es una versión de UNIX con soporte para hilos a nivel
kernel y a nivel usuario, procesamiento simétrico y planificación
en tiempo real.

28. Hilos28
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Soporte de hilos en Solaris 2
LWP – Nivel intermedio entre los hilos a nivel kernel y los hilos
a nivel usuario.

29. Hilos29
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Hilos en Solaris 2. Recursos necesarios para
los tipos de hilos
Hilos del kernel
• Estructura de datos pequeña y un stack
• El intercambio de hilos no requiere cambiar la información del
acceso a memoria
• Cambios de hilos relativamente rápidos

30. Hilos30
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Hilos en Solaris 2. Recursos necesarios para
los tipos de hilos
LWP
• PCB con datos de los registros
• Información sobre la memoria
• El intercambio entre LWP es relativamente lento

31. Hilos31
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Hilos en Solaris 2. Recursos necesarios para
los tipos de hilos
Hilos a nivel usuario
• Solo requiere un stack y un contador de programa
• No involucrar al kernel significa un intercambio rápido
• El kernel solo ve los LWP que soporta los hilos a nivel usuario

32. Hilos32
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Usuario
Núcleo
Hardware
Biblioteca
de hilos
Hilo a nivel de
usuario
Hilo del núcleo Proceso ligero Procesador
LL L LL L L L L
L P
P P P P P
Proceso 1 Proceso 2 Proceso 3 Proceso 4 Proceso 5
Ejemplo de la arquitectura multihilo de
Solaris

33. Hilos33
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Gestión de hilos básica
Un hilo tiene :
• Un identificador (ID)
• Una pila
• Una prioridad de ejecución
• Una dirección de inicio de ejecución.

34. Hilos34
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Gestión de hilos básica
(POSIX)
Se dice que un hilo es dinámico si se puede crear en cualquier
instante durante la ejecución.
En POSIX :
• los hilos se crean dinámicamente con la función
pthread_create.
• pthread_exit termina el hilo que la invoca.

35. Hilos35
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Gestión de hilos básica (POSIX), ejemplo:
Programa que crea un hilo donde muestra el mensaje “Hola
Mundo”
Para compilar el programa :
• $ cc -D_REENTRANT thread2.c -o thread2 -lpthread

36. Hilos36
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int main()
{
pthread_create(a_thread,funcion_hilo);
pthread_join(a_thread);
}
funcion_hilo()
{
…
}
Crea un hilo
nuevo
Espera a que
termine el hilo
creado
Hilo principal
Hilo creado con la llamada
pthread_create

37. Hilos37
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Gestión de hilos básica
(POSIX)
Pthread_join()
• Hilo que ejecuta pthread_join, espera a que termine otro hilo
El hilo principal debe esperar a que terminen todos los hilos
creados
• Si el hilo principal no espera a que terminen los hilos creados,
al terminar termina el proceso con todos los hilos.

38. Hilos38
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Hilos en memoria
Código
(compartido)
Datos
(compartidos)
Int cont=0 (var. Global)
Stack (de cada hilo)
Int i
(var local)
Stack (de cada hilo)
Int i
(var local)