Atomic manipulation in Nginx

Nginx provides its own atomic operation on a processor that does not support atomic operations, but the atomic operation is simulated using the C language:

Static Ngx_inline Ngx_atomic_uint_tngx_atomic_cmp_set (ngx_atomic_t *lock, ngx_atomic_uint_t old,     ngx_atomic_ uint_t set) {     if (*lock = = old) {         *lock = set;         return 1;     }     return 0;}

Static Ngx_inline Ngx_atomic_int_tngx_atomic_fetch_add (ngx_atomic_t *value, ngx_atomic_int_t add) {     ngx_atomic_ int_t old  ;     Old = *value;     *value + = add;     return old;}

for processors that support atomic operations (take x86 as an example):

#define Ngx_smp_lock  "LOCK;" /** "Cmpxchgl  R, [m]":* *     if (eax = = [M]) {*         ZF = 1;*         [m] = r;*     } else {*         ZF = 0;*         eax = [m];*< c8/>}*** the "R" means the general register.* the "=a" and "a" is the%eax register.* although we can return result in an Y register, we use the "a" because it is* used in Cmpxchgl anyway.  The result is actually in%al but not in%eax,* However, as the code was inlined gcc can test%al as well as%eax,* and ICC Adds "Movzbl%al,%eax" by itself.** the "CC" means that flags were changed.*/static ngx_inline Ngx_atomic_uint_tngx_atom Ic_cmp_set (ngx_atomic_t *lock, ngx_atomic_uint_t old,    ngx_atomic_uint_t set) {    U_char  res;    __asm__ volatile (         ngx_smp_lock    "    cmpxchgl  %3,%1;   "    "    Sete      %0;       "    :" =a "(res):" M "(*lock)," a "(old)," R "(SET):" CC "," Memory ");    return res;}

/** "Xaddl  R, [m]":* *     temp = [m];*     [m] + = r;*     r = temp;*** the "+r" means the general register.* the "CC" means that flags were changed.*/static ngx_inline ngx_atomic_int_tngx_atomic_fetch_add (ngx_atomic_t *value, ngx_atomic _int_t add) {    ngx_atomic_uint_t old  ;    __asm__ volatile (         ngx_smp_lock    "    xaddl  %2,%1;   "    : "=a" (old): "M" (*value), "a" (add): "CC" , "Memory");    return old;}

Spin Lock:

/* old ' as ' does not ' support ' pause ' opcode */#define NGX_CPU_PAUSE ()         __asm__ (". Byte 0xf3, 0x90") #define Ngx_sched_yi Eld ()  Sched_yield () voidngx_spinlock (ngx_atomic_t *lock, ngx_atomic_int_t value, ngx_uint_t spin) {#if (ngx_have_ Atomic_ops)    ngx_uint_t  i, N;    for (;;) {        if (*lock = = 0 && ngx_atomic_cmp_set (lock, 0, value)) {            return;        }        if (Ngx_ncpu > 1) {for            (n = 1; n < spin, n <<= 1) {for                (i = 0; i < n; i++) {                    Ngx_cpu_pause ( );                }                if (*lock = = 0 && ngx_atomic_cmp_set (lock, 0, value)) {                    return;                }}        }        Ngx_sched_yield ();    }

Signal:

Ngx_int_tngx_init_signals (ngx_log_t *log) {    ngx_signal_t      *sig;    struct sigaction   sa;    for (sig = Signals; Sig->signo! = 0; sig++) {        Ngx_memzero (&sa, sizeof (struct sigaction));        Sa.sa_handler = sig->handler;        Sigemptyset (&sa.sa_mask);        if (Sigaction (Sig->signo, &sa, NULL) = =-1) {#if (ngx_valgrind)            ngx_log_error (Ngx_log_alert, log, Ngx_errno,                          "Sigaction (%s) failed, ignored", sig->signame); #else            ngx_log_error (Ngx_log_emerg, log, Ngx_errno,                          "Sigaction (%s) failed", sig->signame);            return ngx_error; #endif        }    }    return NGX_OK;}

The above describes the operation of the atom in Nginx, including the aspects of the content, I hope that the PHP tutorial interested in a friend helpful.

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