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Why Pthreads?
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Platformfork() pthread_create()
real user sys real user sysAMD 2.4
GHz Opteron
(8cpus/node)
41.07 60.08 9.01 0.66 0.19 0.43
IBM 1.9 GHz POWER5 p5-575
(8cpus/node)
64.24 30.78 27.68 1.75 0.69 1.10
IBM 1.5 GHz POWER4
(8cpus/node)
104.05 48.64 47.21 2.01 1.00 1.52
INTEL 2.4 GHz Xeon
(2 cpus/node)
54.95 1.54 20.78 1.64 0.67 0.90
INTEL 1.4 GHz
Itanium2 (4 cpus/node)
54.54 1.07 22.22 2.03 1.26 0.67
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Pthread Interface
Pthread 為 POSIX 所定義的 thread 標準界面，它目前已經被移植到許多平台上，因此使用 pthread 會有較好的可移植性。
在 linux 中 pthread 是透過 clone 函式來產生 thread ，因此為 kernel space thread
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執行緒的建立與結束
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Pthread create#include <pthread.h>#include <stdio.h>#define NUM_THREADS 5void *PrintHello(void *threadid){ long tid; tid = (long)threadid; printf("Hello World! It's me, thread #%ld!\n", tid); pthread_exit(NULL);}
int main (int argc, char *argv[]){ pthread_t threads[NUM_THREADS]; int rc; long t; for(t=0; t<NUM_THREADS; t++){ printf("In main: creating thread %ld\n", t); rc = pthread_create(&threads[t], NULL, PrintHello, (void *)t); if (rc){ printf("ERROR; return code from pthread_create() is %d\n",
rc); exit(-1); } } pthread_exit(NULL);}
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Pthread joining
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Joinable or Not?
When a thread is created, one of its attributes defines whether it is joinable or detached. Only threads that are created as joinable can be joined. If a thread is created as detached, it can never be joined.
To explicitly create a thread as joinable or detached, the attr argument in the pthread_create() routine is used. The typical 4 step process is: Declare a pthread attribute variable of the pthread_attr_t data
type Initialize the attribute variable with pthread_attr_init() Set the attribute detached status with
pthread_attr_setdetachstate() When done, free library resources used by the attribute with
pthread_attr_destroy()
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Detaching:
The pthread_detach() routine can be used to explicitly detach a thread even though it was created as joinable.
There is no converse routine.
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例 – thread.c
#include <pthread.h>#include <stdio.h>
void *print_hello(void *argu){ while (1) { printf("Hello,\n"); sleep(1); } return NULL;}
void *print_world(void *argu){ while (1) { printf("World!\n"); sleep(1); } return NULL;}
int main(){ pthread_t thread_id1, thread_id2;
pthread_create(&thread_id1, NULL, &print_hello, NULL);
pthread_create(&thread_id2, NULL, &print_world, NULL);
while (1) { printf("-------------------------\n"); sleep(1); } return 0;}
% gcc –o thread thread.c –lpthread
% ./thread
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例 – thread2.c
#include <pthread.h>#include <stdio.h>#include <string.h>
void *print_hello(void *argu){ while (1) { printf("%s,\n", (char *)argu); sleep(1); } return NULL;}
void *print_world(void *argu){ while (1) { printf("%s!\n", (char *)argu); sleep(1); } return NULL;}
int main(){ pthread_t thread_id1, thread_id2; char thread_argu1[256]; char thread_argu2[256];
strcpy(thread_argu1, "Hello"); strcpy(thread_argu2, "World");
pthread_create(&thread_id1, NULL, &print_hello, thread_argu1);
pthread_create(&thread_id2, NULL, &print_world, thread_argu2);
while (1) { printf("-------------------------\n"); sleep(1); } return 0;}
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等待執行緒結束
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例 – detached.c
#include <pthread.h>#include <stdio.h>
void *print_hello(void *argu){ while (1) { printf("Hello,\n"); sleep(1); }}
void *print_world(void *argu){ while (1) { printf("World!\n"); sleep(1); }}
int main(){ pthread_attr_t attr; pthread_t thread_id1, thread_id2;
/* Create detached threads. */ pthread_attr_init(&attr); pthread_attr_setdetachstate(&attr,
PTHREAD_CREATE_DETACHED);
pthread_create(&thread_id1, &attr, &print_hello, NULL);
pthread_create(&thread_id2, &attr, &print_world, NULL);
return 0;}
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例 – join.c
#include <pthread.h>#include <stdio.h>#include <string.h>void *print_hello(void *argu){ int i; for (i = 0; i < 5; i++) { printf("%s,\n", (char *)argu); sleep(1); } return NULL;}void *print_world(void *argu){ int i; for (i = 0; i < 5; i++) { printf("%s!\n", (char *)argu); sleep(1); } return NULL;}
int main(){ pthread_t thread_id1, thread_id2; char thread_argu1[256]; char thread_argu2[256];
strcpy(thread_argu1, "Hello"); strcpy(thread_argu2, "World");
pthread_create(&thread_id1, NULL, &print_hello, thread_argu1);
pthread_create(&thread_id2, NULL, &print_world, thread_argu2);
pthread_join(thread_id1, NULL); pthread_join(thread_id2, NULL);
printf("--End of The Program.--\n");
return 0;}
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Thread 範例
“serial.c” in the Textbook
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註冊新執行緒產生時所執行的 handler
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process vs. thread
A process = code + control (thread) A thread in a process
Deadlock could happen the "fork-one" model results in duplicating
only the thread that called fork() it is possible that at the time of the call another thread in the
parent owns a lock. This thread is not duplicated in the child, so no thread will unlock this lock in the child. Deadlock occurs if the single thread in the child needs this lock.
The problem is more serious with locks in libraries
