Hi, I did a quick look at the code of the NPTL. I found that the
pthread_self does not return the tid but the address of the struct
pthread which is allocated in the stack (at least on i386 and possibly
on other Arch too). Struct pthread contains various information used
by the pthreaded calls. It created in the stack during pthread
creation. pthread_self just finds the structure from stack and return
its address.
Yes! It is right. I "strace"d the _pid_ file compiled from pid.c, I get
the result as follows(just a snapshot).
clone(child_stack=0xb7f7d4d4,
flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|
CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|
CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID,
parent_tidptr=0xb7f7dbe8,
{entry_number:6, base_addr:0xb7f7dba0, limit:1048575,
seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1,
seg_not_present:0, useable:1},
child_tidptr=0xb7f7dbe8) = 21945
clone(child_stack=0xb757c4d4,
flags=CLONE_VM|CLONE_FS|CLONE_FILES|CLONE_SIGHAND|
CLONE_THREAD|CLONE_SYSVSEM|CLONE_SETTLS|
CLONE_PARENT_SETTID|CLONE_CHILD_CLEARTID,
parent_tidptr=0xb757cbe8,
{entry_number:6, base_addr:0xb757cba0, limit:1048575,
seg_32bit:1, contents:0, read_exec_only:0, limit_in_pages:1,
seg_not_present:0, useable:1},
child_tidptr=0xb757cbe8) = 21946
futex(0xb7f7dbe8, FUTEX_WAIT, 21945, NULL
In the thread 0:posix tid 3086474144
In the thread 0:pid 21944
In the thread 0:tid 21945) = 0
futex(0xb757cbe8, FUTEX_WAIT, 21946, NULL
In the thread 1:posix tid 3075984288
In the thread 1:pid 21944
In the thread 1:tid 21946) = 0
As we see, base_addr:0xb7f7dba0 in the first clone()==
3086474144 in thread 0
while base_addr:0xb757cba0 in the second clone()==
3075984288 in thread 1
Best Regards,
Cheng
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