9e933d9bf
Denys Vlasenko
2011-05-20
Subject
tail: optimize "tail -c HUGENUM REGULAR_FILE". Closes 3763.
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Commit Diff GitHub →
coreutils/tail.c+21 -15
| @@ -59,7 +59,8 @@ static const struct suffix_mult tail_suffixes[] = { | |
| }; | |
| struct globals { | |
| - | bool status; |
| + | bool from_top; |
| + | bool exitcode; |
| } FIX_ALIASING; | |
| #define G (*(struct globals*)&bb_common_bufsiz1) | |
| @@ -85,7 +86,7 @@ static ssize_t tail_read(int fd, char *buf, size_t count) | |
| r = full_read(fd, buf, count); | |
| if (r < 0) { | |
| bb_perror_msg(bb_msg_read_error); | |
| - | G.status = EXIT_FAILURE; |
| + | G.exitcode = EXIT_FAILURE; |
| } | |
| return r; | |
| @@ -99,7 +100,7 @@ static unsigned eat_num(const char *p) | |
| p++; | |
| else if (*p == '+') { | |
| p++; | |
| - | G.status = 1; /* mark that we saw "+" */ |
| + | G.from_top = 1; |
| } | |
| return xatou_sfx(p, tail_suffixes); | |
| } | |
| @@ -109,7 +110,6 @@ int tail_main(int argc, char **argv) | |
| { | |
| unsigned count = 10; | |
| unsigned sleep_period = 1; | |
| - | bool from_top; |
| const char *str_c, *str_n; | |
| char *tailbuf; | |
| @@ -152,8 +152,6 @@ int tail_main(int argc, char **argv) | |
| #endif | |
| argc -= optind; | |
| argv += optind; | |
| - | from_top = G.status; /* 1 if there was "-c +N" or "-n +N" */ |
| - | G.status = EXIT_SUCCESS; |
| /* open all the files */ | |
| fds = xmalloc(sizeof(fds[0]) * (argc + 1)); | |
| @@ -171,7 +169,7 @@ int tail_main(int argc, char **argv) | |
| do { | |
| int fd = open_or_warn_stdin(argv[i]); | |
| if (fd < 0 && !FOLLOW_RETRY) { | |
| - | G.status = EXIT_FAILURE; |
| + | G.exitcode = EXIT_FAILURE; |
| continue; | |
| } | |
| fds[nfiles] = fd; | |
| @@ -183,15 +181,19 @@ int tail_main(int argc, char **argv) | |
| /* prepare the buffer */ | |
| tailbufsize = BUFSIZ; | |
| - | if (!from_top && COUNT_BYTES) { |
| + | if (!G.from_top && COUNT_BYTES) { |
| if (tailbufsize < count + BUFSIZ) { | |
| tailbufsize = count + BUFSIZ; | |
| } | |
| } | |
| - | tailbuf = xmalloc(tailbufsize); |
| + | /* tail -c1024m REGULAR_FILE doesn't really need 1G mem block. |
| + | * (In fact, it doesn't need ANY memory). So delay allocation. |
| + | */ |
| + | tailbuf = NULL; |
| /* tail the files */ | |
| - | fmt = header_fmt_str + 1; /* skip header leading newline on first output */ |
| + | |
| + | fmt = header_fmt_str + 1; /* skip leading newline in the header on the first output */ |
| i = 0; | |
| do { | |
| char *buf; | |
| @@ -209,7 +211,7 @@ int tail_main(int argc, char **argv) | |
| fmt = header_fmt_str; | |
| } | |
| - | if (!from_top) { |
| + | if (!G.from_top) { |
| off_t current = lseek(fd, 0, SEEK_END); | |
| if (current > 0) { | |
| unsigned off; | |
| @@ -242,6 +244,9 @@ int tail_main(int argc, char **argv) | |
| } | |
| } | |
| + | if (!tailbuf) |
| + | tailbuf = xmalloc(tailbufsize); |
| + | |
| buf = tailbuf; | |
| taillen = 0; | |
| /* "We saw 1st line/byte". | |
| @@ -249,7 +254,7 @@ int tail_main(int argc, char **argv) | |
| seen = 1; | |
| newlines_seen = 0; | |
| while ((nread = tail_read(fd, buf, tailbufsize-taillen)) > 0) { | |
| - | if (from_top) { |
| + | if (G.from_top) { |
| int nwrite = nread; | |
| if (seen < count) { | |
| /* We need to skip a few more bytes/lines */ | |
| @@ -313,7 +318,7 @@ int tail_main(int argc, char **argv) | |
| buf = tailbuf + taillen; | |
| } | |
| } /* while (tail_read() > 0) */ | |
| - | if (!from_top) { |
| + | if (!G.from_top) { |
| xwrite(STDOUT_FILENO, tailbuf, taillen); | |
| } | |
| } while (++i < nfiles); | |
| @@ -368,10 +373,11 @@ int tail_main(int argc, char **argv) | |
| xwrite(STDOUT_FILENO, tailbuf, nread); | |
| } | |
| } while (++i < nfiles); | |
| - | } |
| + | } /* while (1) */ |
| + | |
| if (ENABLE_FEATURE_CLEAN_UP) { | |
| free(fds); | |
| free(tailbuf); | |
| } | |
| - | return G.status; |
| + | return G.exitcode; |
| } | |