1，验证代码转载

#include
#include
#include
#include
#include

sem_t sem_a;
void *task1();

int main(void){

int ret=0;
pthread_t thrd1;
sem_init(&sem_a,0,1);

//create children process
ret=pthread_create(&thrd1,NULL,task1,NULL);

//waiting for children process end
pthread_join(thrd1,NULL);
}

void *task1()
{

int sval = 0;

//holding the semaphore
sem_wait(&sem_a);

sleep(5); //do_nothing
sem_getvalue(&sem_a,&sval);
printf(“sem value = %d\n”,sval);
//release the semaphore
sem_post(&sem_a);

}

执行反馈结果：

sem value = 0

2，gcc -o t_mutex t_mutex -lpthread

备注：pthread库不是Linux系统默认的库，连接时需要使用静态库libpthread.a，所以在线程函数在编译时，需要连接库函数

3，跟踪执行过程

strace -o t1_mutex.str ./t1_mutex

sem value = 0
[root@SZB-L0004396 appcode]# less t1_mutex.str
execve(“./t1_mutex”, [“./t1_mutex”], [/* 19 vars */]) = 0
brk(0) = 0x237e000
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fac07ffe000
access(“/etc/ld.so.preload”, R_OK) = -1 ENOENT (No such file or directory)
open(“/etc/ld.so.cache”, O_RDONLY|O_CLOEXEC) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=72041, …}) = 0
mmap(NULL, 72041, PROT_READ, MAP_PRIVATE, 3, 0) = 0x7fac07fec000
close(3) = 0
open(“/lib64/libpthread.so.0”, O_RDONLY|O_CLOEXEC) = 3
read(3, “\177ELF\2\1\1\0\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\240l\0\0\0\0\0\0″…, 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=141616, …}) = 0
mmap(NULL, 2208864, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fac07bc3000
mprotect(0x7fac07bd9000, 2097152, PROT_NONE) = 0
mmap(0x7fac07dd9000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x16000) = 0x7fac07dd9000
mmap(0x7fac07ddb000, 13408, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fac07ddb000
close(3) = 0
open(“/lib64/libc.so.6”, O_RDONLY|O_CLOEXEC) = 3
read(3, “\177ELF\2\1\1\3\0\0\0\0\0\0\0\0\3\0>\0\1\0\0\0\0\34\2\0\0\0\0\0″…, 832) = 832
fstat(3, {st_mode=S_IFREG|0755, st_size=2107768, …}) = 0
mmap(NULL, 3932736, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x7fac07802000
mprotect(0x7fac079b8000, 2097152, PROT_NONE) = 0
mmap(0x7fac07bb8000, 24576, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1b6000) = 0x7fac07bb8000
mmap(0x7fac07bbe000, 16960, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x7fac07bbe000
close(3) = 0
mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fac07feb000
mmap(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x7fac07fe9000
arch_prctl(ARCH_SET_FS, 0x7fac07fe9740) = 0
mprotect(0x7fac07bb8000, 16384, PROT_READ) = 0
mprotect(0x7fac07dd9000, 4096, PROT_READ) = 0
mprotect(0x600000, 4096, PROT_READ) = 0
mprotect(0x7fac07fff000, 4096, PROT_READ) = 0
munmap(0x7fac07fec000, 72041) = 0
set_tid_address(0x7fac07fe9a10) = 9159
set_robust_list(0x7fac07fe9a20, 24) = 0
rt_sigaction(SIGRTMIN, {0x7fac07bc9780, [], SA_RESTORER|SA_SIGINFO, 0x7fac07bd2130}, NULL, 8) = 0
rt_sigaction(SIGRT_1, {0x7fac07bc9810, [], SA_RESTORER|SA_RESTART|SA_SIGINFO, 0x7fac07bd2130}, NULL, 8) = 0
rt_sigprocmask(SIG_UNBLOCK, [RTMIN RT_1], NULL, 8) = 0
getrlimit(RLIMIT_STACK, {rlim_cur=8192*1024, rlim_max=RLIM64_INFINITY}) = 0
mmap(NULL, 8392704, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS|MAP_STACK, -1, 0) = 0x7fac07001000
brk(0) = 0x237e000
brk(0x239f000) = 0x239f000
brk(0) = 0x239f000
mprotect(0x7fac07001000, 4096, PROT_NONE) = 0
clone(child_stack=0x7fac07800fb0, flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID, parent_tidptr=0x7fac078019d0, tls=0x7fac07801700, child_tidptr=0x7fac078019d0) = 9160
futex(0x7fac078019d0, FUTEX_WAIT, 9160, NULL) = 0
exit_group(0) = ?
+++ exited with 0 +++