README.md

@@ -327,16 +327,17 @@ the first request's) stops waiting for a processing slot, or, once it has one,
 gives it back without beginning to encode. A request waiting for a shared
 transcode that stops this way is answered 503 with the error
 `server busy, try again later`, though its own `downstream_timeout` may not have
-ended. libvips cannot stop an encode once it has begun, so an encode keeps its
-slot until it finishes, which can be after `downstream_timeout`. The limit of
-8192 on each side of the source and of the output bounds how long that takes.
-With one libvips thread, as pixad runs it, encoding 8192x8192 random pixels
-takes up to about 1 second as JPEG, 15 as PNG, 16 as GIF, 63 as WebP, 110 as
-AVIF and 96 as JPEG XL, the slowest of 8 or 16 bits per sample, with or without
-an alpha channel. WebP, AVIF and JPEG XL are that slow only with an alpha
-channel: 8-bit RGB takes about 44, 53 and 28 seconds. Decoding such a source
-adds up to about 11 seconds. A WebP, AVIF or JPEG XL encode can therefore hold
-its slot past the default `downstream_timeout` of 60 seconds.
+ended. govips gives pixa no way to stop libvips once an encode has begun, so an
+encode keeps its slot until it finishes, which can be after
+`downstream_timeout`. The limit of 8192 on each side of the source and of the
+output bounds how long that takes. With one libvips thread, as pixad runs it,
+encoding 8192x8192 random pixels takes up to about 1 second as JPEG, 15 as PNG,
+16 as GIF, 63 as WebP, 110 as AVIF and 96 as JPEG XL, the slowest of 8 or 16
+bits per sample, with or without an alpha channel. WebP, AVIF and JPEG XL are
+that slow only with an alpha channel: 8-bit RGB takes about 44, 53 and 28
+seconds. Decoding such a source adds up to about 11 seconds. A WebP, AVIF or
+JPEG XL encode can therefore hold its slot past the default `downstream_timeout`
+of 60 seconds.
 
 The login form (`POST /`) is limited to 5 attempts per minute per client
 address, counting an IPv6 client by its /64; an attempt over the limit is

TODO.md

@@ -65,16 +65,16 @@ P2: security: per-origin rate limiting
   slot back, when the context has ended by the time it has the slot or before it
   encodes. A request that waited for a shared transcode stopped at the first
   request's deadline is answered 503 `server busy, try again later`, not 500,
-  though its own `downstream_timeout` may not have ended. libvips cannot stop an
-  encode once it has begun, so that encode keeps its slot until it finishes; the
-  limit of 8192 on each side of the source and of the output bounds how long
-  that takes. With one libvips thread, 8192x8192 random pixels take up to about
-  1 second to encode as JPEG, 15 as PNG, 16 as GIF, 63 as WebP, 110 as AVIF and
-  96 as JPEG XL, the last three with an alpha channel, plus up to about 11
-  seconds to decode the source; `README.md` gives these times and no longer says
-  the work stops when `downstream_timeout` ends. The settings of the WebP, AVIF
-  and JPEG XL encoders, which can hold a slot past the default
-  `downstream_timeout` of 60 seconds, are unchanged.
+  though its own `downstream_timeout` may not have ended. govips gives pixa no
+  way to stop libvips once an encode has begun, so that encode keeps its slot
+  until it finishes; the limit of 8192 on each side of the source and of the
+  output bounds how long that takes. With one libvips thread, 8192x8192 random
+  pixels take up to about 1 second to encode as JPEG, 15 as PNG, 16 as GIF, 63
+  as WebP, 110 as AVIF and 96 as JPEG XL, the last three with an alpha channel,
+  plus up to about 11 seconds to decode the source; `README.md` gives these
+  times and no longer says the work stops when `downstream_timeout` ends. The
+  settings of the WebP, AVIF and JPEG XL encoders, which can hold a slot past
+  the default `downstream_timeout` of 60 seconds, are unchanged.
 - 2026-10-15 a cached variant is served while its source URL is in the negative
   cache (closes #245): `Get` checked the negative cache before the variant
   cache, so once a fetch of the source failed, as one does when another variant

internal/imageprocessor/imageprocessor.go

@@ -209,8 +209,9 @@ func New(params Params) *ImageProcessor {
 // MaxConcurrentProcessing images are already being processed, it waits up
 // to ProcessingWaitTimeout for one to finish, then fails with
 // ErrTooManyImages. When ctx has ended once Process has a slot, or before it
-// encodes, it returns ctx's error and gives the slot back. libvips cannot stop
-// an encode once it has begun, so an encode keeps its slot until it finishes.
+// encodes, it returns ctx's error and gives the slot back. govips gives pixa
+// no way to stop libvips once an encode has begun, so an encode keeps its
+// slot until it finishes.
 func (p *ImageProcessor) Process(
 	ctx context.Context,
 	input io.Reader,
@@ -532,9 +533,9 @@ func (p *ImageProcessor) resize(
 
 const defaultQuality = 85
 
-// encode encodes an image to the specified format. libvips cannot stop an
-// encode once it has begun, so when ctx has ended encode returns ctx's error
-// without beginning one.
+// encode encodes an image to the specified format. govips gives pixa no way
+// to stop libvips once an encode has begun, so when ctx has ended encode
+// returns ctx's error without beginning one.
 func (p *ImageProcessor) encode(
 	ctx context.Context, img *vips.ImageRef, format Format, quality int,
 ) ([]byte, error) {
@@ -644,10 +645,11 @@ func exportWebP(img *vips.ImageRef, quality int) ([]byte, error) {
 
 // avifEffort is the AVIF effort, from 0 (fastest) to 9; 1 is the lowest
 // govips can set. With one thread, as pixad runs libvips, 1 takes about 51
-// seconds to save an 8192x8192 image of random pixels, the worst case,
-// against the default downstream_timeout of 60 seconds. On an image of
-// milder noise, which 1 saves in about 12 seconds, 2 takes nearly a minute
-// and libvips' default, 4, takes minutes.
+// seconds to save an 8192x8192 RGB image of random pixels, and about 110
+// with an alpha channel, the worst case, against the default
+// downstream_timeout of 60 seconds. On an image of milder noise, which 1
+// saves in about 12 seconds, 2 takes nearly a minute and libvips' default,
+// 4, takes minutes.
 const avifEffort = 1
 
 // avifBitdepth is the AVIF bit depth, 8 bits per sample for every image.