Praca s vlaknami

Vlakna v pthreade maju niekolko zakuti:

pthread_cond_wait v kombinacii so pthread_cond_signal moze skoncit v neprijemnom death-locku: 1. vlakno sa snazi nieco poslat 2. vlakno pocuva a v pripade zaujimavej udalosti zavola funkciu DataReceive

1. vlakno vola: lock Application lock Library pthread_cond_wait unlock Library unlock Application

2. vlakno vola dokolecka: lock Library kontrola_spojenia ak send presiel: pthread_cond_signal unlock Library (*) … … lock Library (*) ak zaujimava udalost zavola DataReceive unlock Library

Problem nastane vtedy ak DataReceive bude v sebe obsahovat Lock Application (napr. na aplikacne data - co moze byt korektna poziadavka). Ak sa stane, ze sa system nepresheduluje medzi unlock a lock Library (oznacene *) tak sa ani nikdy z cond_waitu nedostane thread, lebo ostane v mutexe ktory drzi aj DataReceive.

TODO: obrazok, lebo je to neprehladne

Majme situaciu, ze niektore vlakno co by nemalo stoji na locku. Zsitit ktoremu vlaknu patri lock sa da cez gdb v premennej pthreadu data.owner:

(gdb) thread 2 - prepneme do vlakna 2
[Switching to thread 2 (Thread 0xb6d94b90 (LWP 22026))]#0  0xb771f424 in __kernel_vsyscall ()
(gdb) bt
#0  0xb771f424 in __kernel_vsyscall ()
#1  0xb76fec99 in __lll_lock_wait () from /lib/i686/cmov/libpthread.so.0
#2  0xb76fa0c4 in _L_lock_89 () from /lib/i686/cmov/libpthread.so.0
#3  0xb76f99f2 in pthread_mutex_lock () from /lib/i686/cmov/libpthread.so.0
#4  0x080484a6 in thread (x=0x0) at mutex_owner.c:8
#5  0xb76f84c0 in start_thread () from /lib/i686/cmov/libpthread.so.0
#6  0xb767784e in clone () from /lib/i686/cmov/libc.so.6
(gdb) up 4 - vo framestacku sa dostaneme na uroven 4 (v QtCreatore staci klik :-) )
#4  0x080484a6 in thread (x=0x0) at mutex_owner.c:8
8               pthread_mutex_lock(&mutex);
(gdb) print mutex.__data.__owner - vypiseme ttid
$1 = 22025
(gdb)

Ktore vlakno to je sa da cez:

ps -eLf

pripade vypis debug infa to zobrazuje ako LWP.

Hrubym su relativne caso pouzivane funkcie.

asctime() basename() catgets() crypt() ctime() dbm_clearerr() dbm_close() dbm_delete() dbm_error() dbm_fetch() dbm_firstkey() dbm_nextkey() dbm_open() dbm_store() dirname() dlerror() drand48() ecvt() encrypt() endgrent() endpwent() endutxent() fcvt() ftw() gcvt() getc_unlocked() getchar_unlocked() getdate() getenv() getgrent() getgrgid() getgrnam() gethostbyaddr() gethostbyname() gethostent() getlogin() getnetbyaddr() getnetbyname() getnetent() getopt() getprotobyname() getprotobynumber() getprotoent() getpwent() getpwnam() getpwuid() getservbyname() getservbyport() getservent() getutxent() getutxid() getutxline() gmtime() hcreate() hdestroy() hsearch() inet_ntoa() l64a() lgamma() lgammaf() lgammal() localeconv() localtime() lrand48() mrand48() nftw() nl_langinfo() ptsname() putc_unlocked() putchar_unlocked() putenv() pututxline() rand() readdir() setenv() setgrent() setkey() setpwent() setutxent() strerror() strtok() ttyname() unsetenv() wcstombs() wctomb()