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| author | Denys Vlasenko <vda.linux@googlemail.com> | 2017-07-25 20:31:14 +0200 |
|---|---|---|
| committer | Denys Vlasenko <vda.linux@googlemail.com> | 2017-07-25 20:31:14 +0200 |
| commit | 1e3e2ccd5dd280371c9ca29c0e0304a0d40592af (patch) | |
| tree | 2a6151351436d06fe61e60b4e71e8deab6378d7c /shell/ash.c | |
| parent | 86981e3ad2d03e77d1f668ac1603a041be448dae (diff) | |
| download | busybox-w32-1e3e2ccd5dd280371c9ca29c0e0304a0d40592af.tar.gz busybox-w32-1e3e2ccd5dd280371c9ca29c0e0304a0d40592af.tar.bz2 busybox-w32-1e3e2ccd5dd280371c9ca29c0e0304a0d40592af.zip | |
ash: [SHELL] Optimize dash -c "command" to avoid a fork
Upstream commit:
Date: Thu, 7 Jul 2011 13:58:48 +0800
[SHELL] Optimize dash -c "command" to avoid a fork
On Sun, Apr 10, 2011 at 07:36:49AM +0000, Jonathan Nieder wrote:
> From: Jilles Tjoelker <jilles@stack.nl>
> Date: Sat, 13 Jun 2009 16:17:45 -0500
>
> This change only affects strings passed to -c, when the -s option is
> not used.
>
> Use the EV_EXIT flag to inform the eval machinery that the string
> being passed is the entirety of input. This way, a fork may be
> omitted in many special cases.
>
> If there are empty lines after the last command, the evalcmd will not
> see the end early enough and forks will not be omitted. The same thing
> seems to happen in bash.
>
> Example:
> sh -c 'ps lT'
> No longer shows a shell process waiting for ps to finish.
>
> [jn: ported from FreeBSD SVN r194128. Bugs are mine.]
>
> Signed-off-by: Jonathan Nieder <jrnieder@gmail.com>
Instead of detecting EOF using the input layer, I'm going to
use the parser instead. In either case, we always have to read
ahead in order to complete the parsing of the previous node.
Therefore we always know whether there is more to come, except
in the case where we see a newline/semicolon or similar.
For the purposes of sh -c, this should be sufficient.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
function old new delta
evalstring 190 224 +34
ash_main 1014 1022 +8
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/0 up/down: 42/0) Total: 42 bytes
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
Diffstat (limited to 'shell/ash.c')
| -rw-r--r-- | shell/ash.c | 18 |
1 files changed, 11 insertions, 7 deletions
diff --git a/shell/ash.c b/shell/ash.c index 42e14cbc8..c96ec939e 100644 --- a/shell/ash.c +++ b/shell/ash.c | |||
| @@ -6128,7 +6128,9 @@ struct backcmd { /* result of evalbackcmd */ | |||
| 6128 | }; | 6128 | }; |
| 6129 | 6129 | ||
| 6130 | /* These forward decls are needed to use "eval" code for backticks handling: */ | 6130 | /* These forward decls are needed to use "eval" code for backticks handling: */ |
| 6131 | #define EV_EXIT 01 /* exit after evaluating tree */ | 6131 | /* flags in argument to evaltree */ |
| 6132 | #define EV_EXIT 01 /* exit after evaluating tree */ | ||
| 6133 | #define EV_TESTED 02 /* exit status is checked; ignore -e flag */ | ||
| 6132 | static int evaltree(union node *, int); | 6134 | static int evaltree(union node *, int); |
| 6133 | 6135 | ||
| 6134 | static void FAST_FUNC | 6136 | static void FAST_FUNC |
| @@ -8345,10 +8347,6 @@ commandcmd(int argc UNUSED_PARAM, char **argv UNUSED_PARAM) | |||
| 8345 | static void *funcblock; /* block to allocate function from */ | 8347 | static void *funcblock; /* block to allocate function from */ |
| 8346 | static char *funcstring_end; /* end of block to allocate strings from */ | 8348 | static char *funcstring_end; /* end of block to allocate strings from */ |
| 8347 | 8349 | ||
| 8348 | /* flags in argument to evaltree */ | ||
| 8349 | #define EV_EXIT 01 /* exit after evaluating tree */ | ||
| 8350 | #define EV_TESTED 02 /* exit status is checked; ignore -e flag */ | ||
| 8351 | |||
| 8352 | static const uint8_t nodesize[N_NUMBER] ALIGN1 = { | 8350 | static const uint8_t nodesize[N_NUMBER] ALIGN1 = { |
| 8353 | [NCMD ] = SHELL_ALIGN(sizeof(struct ncmd)), | 8351 | [NCMD ] = SHELL_ALIGN(sizeof(struct ncmd)), |
| 8354 | [NPIPE ] = SHELL_ALIGN(sizeof(struct npipe)), | 8352 | [NPIPE ] = SHELL_ALIGN(sizeof(struct npipe)), |
| @@ -12491,6 +12489,12 @@ expandstr(const char *ps) | |||
| 12491 | return stackblock(); | 12489 | return stackblock(); |
| 12492 | } | 12490 | } |
| 12493 | 12491 | ||
| 12492 | static inline int | ||
| 12493 | parser_eof(void) | ||
| 12494 | { | ||
| 12495 | return tokpushback && lasttoken == TEOF; | ||
| 12496 | } | ||
| 12497 | |||
| 12494 | /* | 12498 | /* |
| 12495 | * Execute a command or commands contained in a string. | 12499 | * Execute a command or commands contained in a string. |
| 12496 | */ | 12500 | */ |
| @@ -12526,7 +12530,7 @@ evalstring(char *s, int flags) | |||
| 12526 | while ((n = parsecmd(0)) != NODE_EOF) { | 12530 | while ((n = parsecmd(0)) != NODE_EOF) { |
| 12527 | int i; | 12531 | int i; |
| 12528 | 12532 | ||
| 12529 | i = evaltree(n, flags); | 12533 | i = evaltree(n, flags & ~(parser_eof() ? 0 : EV_EXIT)); |
| 12530 | if (n) | 12534 | if (n) |
| 12531 | status = i; | 12535 | status = i; |
| 12532 | popstackmark(&smark); | 12536 | popstackmark(&smark); |
| @@ -13671,7 +13675,7 @@ int ash_main(int argc UNUSED_PARAM, char **argv) | |||
| 13671 | // if (!sflag) g_parsefile->pf_fd = -1; | 13675 | // if (!sflag) g_parsefile->pf_fd = -1; |
| 13672 | // ^^ not necessary since now we special-case fd 0 | 13676 | // ^^ not necessary since now we special-case fd 0 |
| 13673 | // in is_hidden_fd() to not be considered "hidden fd" | 13677 | // in is_hidden_fd() to not be considered "hidden fd" |
| 13674 | evalstring(minusc, 0); | 13678 | evalstring(minusc, sflag ? 0 : EV_EXIT); |
| 13675 | } | 13679 | } |
| 13676 | 13680 | ||
| 13677 | if (sflag || minusc == NULL) { | 13681 | if (sflag || minusc == NULL) { |