Linux can create thread

NAME

pthread_create - create a new thread

SYNOPSIS

#include pthread.h> int pthread_create(pthread_t *thread, const pthread_attr_t *attr, void *(*start_routine) (void *), void *arg); Compile and link with -pthread.

DESCRIPTION

The pthread_create() function starts a new thread in the calling process. The new thread starts execution by invoking start_routine(); arg is passed as the sole argument of start_routine(). The new thread terminates in one of the following ways: * It calls pthread_exit(3), specifying an exit status value that is available to another thread in the same process that calls pthread_join(3). * It returns from start_routine(). This is equivalent to calling pthread_exit(3) with the value supplied in the return statement. * It is canceled (see pthread_cancel(3)). * Any of the threads in the process calls exit(3), or the main thread performs a return from main(). This causes the termination of all threads in the process. The attr argument points to a pthread_attr_t structure whose contents are used at thread creation time to determine attributes for the new thread; this structure is initialized using pthread_attr_init(3) and related functions. If attr is NULL, then the thread is created with default attributes. Before returning, a successful call to pthread_create() stores the ID of the new thread in the buffer pointed to by thread; this identifier is used to refer to the thread in subsequent calls to other pthreads functions. The new thread inherits a copy of the creating thread's signal mask (pthread_sigmask(3)). The set of pending signals for the new thread is empty (sigpending(2)). The new thread does not inherit the creating thread's alternate signal stack (sigaltstack(2)). The new thread inherits the calling thread's floating-point environment (fenv(3)). The initial value of the new thread's CPU-time clock is 0 (see pthread_getcpuclockid(3)). Linux-specific details The new thread inherits copies of the calling thread's capability sets (see capabilities(7)) and CPU affinity mask (see sched_setaffinity(2)).

RETURN VALUE

On success, pthread_create() returns 0; on error, it returns an error number, and the contents of *thread are undefined.

ERRORS

EAGAIN Insufficient resources to create another thread. EAGAIN A system-imposed limit on the number of threads was encountered. There are a number of limits that may trigger this error: the RLIMIT_NPROC soft resource limit (set via setrlimit(2)), which limits the number of processes and threads for a real user ID, was reached; the kernel's system-wide limit on the number of processes and threads, /proc/sys/kernel/threads-max, was reached (see proc(5)); or the maximum number of PIDs, /proc/sys/kernel/pid_max, was reached (see proc(5)). EINVAL Invalid settings in attr. EPERM No permission to set the scheduling policy and parameters specified in attr.

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7). ┌─────────────────┬───────────────┬─────────┐ │Interface │ Attribute │ Value │ ├─────────────────┼───────────────┼─────────┤ │pthread_create() │ Thread safety │ MT-Safe │ └─────────────────┴───────────────┴─────────┘

CONFORMING TO

NOTES

See pthread_self(3) for further information on the thread ID returned in *thread by pthread_create(). Unless real-time scheduling policies are being employed, after a call to pthread_create(), it is indeterminate which thread—the caller or the new thread—will next execute. A thread may either be joinable or detached. If a thread is joinable, then another thread can call pthread_join(3) to wait for the thread to terminate and fetch its exit status. Only when a terminated joinable thread has been joined are the last of its resources released back to the system. When a detached thread terminates, its resources are automatically released back to the system: it is not possible to join with the thread in order to obtain its exit status. Making a thread detached is useful for some types of daemon threads whose exit status the application does not need to care about. By default, a new thread is created in a joinable state, unless attr was set to create the thread in a detached state (using pthread_attr_setdetachstate(3)). Under the NPTL threading implementation, if the RLIMIT_STACK soft resource limit at the time the program started has any value other than "unlimited", then it determines the default stack size of new threads. Using pthread_attr_setstacksize(3), the stack size attribute can be explicitly set in the attr argument used to create a thread, in order to obtain a stack size other than the default. If the RLIMIT_STACK resource limit is set to "unlimited", a per-architecture value is used for the stack size. Here is the value for a few architectures: ┌─────────────┬────────────────────┐ │Architecture │ Default stack size │ ├─────────────┼────────────────────┤ │i386 │ 2 MB │ ├─────────────┼────────────────────┤ │IA-64 │ 32 MB │ ├─────────────┼────────────────────┤ │PowerPC │ 4 MB │ ├─────────────┼────────────────────┤ │S/390 │ 2 MB │ ├─────────────┼────────────────────┤ │Sparc-32 │ 2 MB │ ├─────────────┼────────────────────┤ │Sparc-64 │ 4 MB │ ├─────────────┼────────────────────┤ │x86_64 │ 2 MB │ └─────────────┴────────────────────┘

BUGS

EXAMPLE

The program below demonstrates the use of pthread_create(), as well as a number of other functions in the pthreads API. In the following run, on a system providing the NPTL threading implementation, the stack size defaults to the value given by the "stack size" resource limit: $ ulimit -s 8192 # The stack size limit is 8 MB (0x800000 bytes) $ ./a.out hola salut servus Thread 1: top of stack near 0xb7dd03b8; argv_string=hola Thread 2: top of stack near 0xb75cf3b8; argv_string=salut Thread 3: top of stack near 0xb6dce3b8; argv_string=servus Joined with thread 1; returned value was HOLA Joined with thread 2; returned value was SALUT Joined with thread 3; returned value was SERVUS In the next run, the program explicitly sets a stack size of 1 MB (using pthread_attr_setstacksize(3)) for the created threads: $ ./a.out -s 0x100000 hola salut servus Thread 1: top of stack near 0xb7d723b8; argv_string=hola Thread 2: top of stack near 0xb7c713b8; argv_string=salut Thread 3: top of stack near 0xb7b703b8; argv_string=servus Joined with thread 1; returned value was HOLA Joined with thread 2; returned value was SALUT Joined with thread 3; returned value was SERVUS Program source #include pthread.h> #include string.h> #include stdio.h> #include stdlib.h> #include unistd.h> #include errno.h> #include ctype.h> #define handle_error_en(en, msg) \ do < errno = en; perror(msg); exit(EXIT_FAILURE); > while (0) #define handle_error(msg) \ do < perror(msg); exit(EXIT_FAILURE); > while (0) struct thread_info < /* Used as argument to thread_start() */ pthread_t thread_id; /* ID returned by pthread_create() */ int thread_num; /* Application-defined thread # */ char *argv_string; /* From command-line argument */ >; /* Thread start function: display address near top of our stack, and return upper-cased copy of argv_string */ static void * thread_start(void *arg) < struct thread_info *tinfo = arg; char *uargv, *p; printf("Thread %d: top of stack near %p; argv_string=%s\n", tinfo->thread_num, &p, tinfo->argv_string); uargv = strdup(tinfo->argv_string); if (uargv == NULL) handle_error("strdup"); for (p = uargv; *p != '\0'; p++) *p = toupper(*p); return uargv; > int main(int argc, char *argv[]) < int s, tnum, opt, num_threads; struct thread_info *tinfo; pthread_attr_t attr; int stack_size; void *res; /* The "-s" option specifies a stack size for our threads */ stack_size = -1; while ((opt = getopt(argc, argv, "s:")) != -1) < switch (opt) < case 's': stack_size = strtoul(optarg, NULL, 0); break; default: fprintf(stderr, "Usage: %s [-s stack-size] arg. \n", argv[0]); exit(EXIT_FAILURE); >> num_threads = argc - optind; /* Initialize thread creation attributes */ s = pthread_attr_init(&attr); if (s != 0) handle_error_en(s, "pthread_attr_init"); if (stack_size > 0) < s = pthread_attr_setstacksize(&attr, stack_size); if (s != 0) handle_error_en(s, "pthread_attr_setstacksize"); >/* Allocate memory for pthread_create() arguments */ tinfo = calloc(num_threads, sizeof(struct thread_info)); if (tinfo == NULL) handle_error("calloc"); /* Create one thread for each command-line argument */ for (tnum = 0; tnum < num_threads; tnum++) < tinfo[tnum].thread_num = tnum + 1; tinfo[tnum].argv_string = argv[optind + tnum]; /* The pthread_create() call stores the thread ID into corresponding element of tinfo[] */ s = pthread_create(&tinfo[tnum].thread_id, &attr, &thread_start, &tinfo[tnum]); if (s != 0) handle_error_en(s, "pthread_create"); >/* Destroy the thread attributes object, since it is no longer needed */ s = pthread_attr_destroy(&attr); if (s != 0) handle_error_en(s, "pthread_attr_destroy"); /* Now join with each thread, and display its returned value */ for (tnum = 0; tnum < num_threads; tnum++) < s = pthread_join(tinfo[tnum].thread_id, &res); if (s != 0) handle_error_en(s, "pthread_join"); printf("Joined with thread %d; returned value was %s\n", tinfo[tnum].thread_num, (char *) res); free(res); /* Free memory allocated by thread */ >free(tinfo); exit(EXIT_SUCCESS); >

COLOPHON

This page is part of release 5.05 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

Источник

Introduction to Linux – Create Thread (Part 15/24)

We know about thread in Linux. In this tutorial, I will explain how to create thread in Linux with the help of a programming example. Thread must be executed in process. It is much similar to a process. We can say that thread is light weight process and shares the same address space, data and attribute of process. Thread is single sequence stream within the process. It is like some mathematical or some small function of code which is run within the process. Refer to the tutorial Thread in Linux.

Fig. 1: Overview of Thread in LINUX

The POSIX thread libraries are available which include different functions regarding the thread. It is a standard library named .

You can create a new thread by pthread_t data type.

System Call pthread_create ( )

System call pthread_create ( ) creates a new thread in the current process.

int pthread_create (pthread_t *thread, const pthread_attr_t *attr, void *(*start_routine) (void *), void *arg);

Execution of new thread starts by invoking start_routine ( ) and arg is passing argument of routine. New thread name is pointed by thread and the attr argument points to a pthread_attr_t structure whose contents are used to determine attributes for the new thread. The thread is created with default attributes if attr is NULL. If pthread_create ( ) is successfully called, it stores the ID of new thread in buffer pointed to thread.

The system call pthread_create() returns zero if new thread is successfully created and it returns error number if not created due to any one of the following errors:

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EAGAIN – Requirement of resources are not fully satisfied to create another thread.

EAGAIN – This error will occur when the number of thread creation limits reaches at threshold level.

EINVAL – It indicates the attr is not valid for creating new thread

EPERM – No permission to set the scheduling policy and parameters specified in attr.

Let’s explain how to create thread by system call thread_create ( ) and how to work upon it. Here I have described a simple demo of creation of thread in c programming. If you are unaware about the basics of C language, refer to the tutorial how to make first C programming in Linux.

void *eventToPrint( void *str );

pthread_t thread1, thread2;

printf(“n Thread 1 created successfullyn”);

perror(“Sorry….Thread 1 is not created. n”);

printf (“n Thread 2 created successfullyn”);

perror(“Sorry….Thread 2 is not created. n”);

pthread_join( thread1, NULL);

pthread_join( thread2, NULL);

void *eventToPrint( void *str )

Save the file in directory and compile it. After the successful compilation, run the executable file from command terminal. You may refer to the tutorial how to make first C programming in Linux if you not aware of compilation and execution process.

Here I have created two new threads for display message. First thread displays “Welcome User” and second thread displays “Hello Enigneersgarage” on screen. Before calling pthread_ create ( ), I have assigned address to thread by thread_t data type. When pthread_create ( ) is calling it will be passed by first argument pthread_t *thread and it will store the ID in address space.

The function eventToPrint ( ) displays the thread message on screen. Message is displayed by routine function eventToPrint ( ) which is passed as sub routine argument in system call. I declared the message of first thread as outside of system call and passed by reference. Message of second thread is directly defined in argument arg with system call pthread_create ( ).

If first thread is created successfully, it returns zero and displays the following message in screen:

Thread 1 created successfully

It displays the error number with following message if creation of thread is failed:

Sorry….Thread 1 is not created.

Same thing happens when second thread is created.

The system call pthread_join ( ) waits for completion of the task of thread. If you do not join the thread, it terminates as soon as it is completed. If pthread_join ( ) is cancelled to join thread, it returns zero and current thread remains joined. I attached both the threads by pthread_join ( ) waiting for one thread when another thread is being executed.

Output of above code will be printed on screen as follows:

Thread 1 created successfully

Thread 2 created successfully

Welcome User

Hello Engineersgarage

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Источник

Linux can create thread