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+ Wed, 02 Feb 2011 16:12:21 -0000\r
+From: Thomas Schwinge <thomas@schwinge.name>\r
+To: notmuch@notmuchmail.org\r
+Subject: Re: [BUG] Emacs UI dropping every 25th line, roughly\r
+In-Reply-To: <87tygqm7g4.fsf@kepler.schwinge.homeip.net>\r
+References: <87tygqm7g4.fsf@kepler.schwinge.homeip.net>\r
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+Date: Wed, 02 Feb 2011 17:12:16 +0100\r
+Message-ID: <87zkqeiffj.fsf@kepler.schwinge.homeip.net>\r
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+--=-=-=\r
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+\r
+Hallo!\r
+\r
+On Sun, 30 Jan 2011 22:02:03 +0100, I wrote:\r
+> That is, roughly every 25th line is dropped in the Emacs notmuch-search\r
+> buffer! (Via setting notmuch-command to a shell script, I intercepted\r
+> the notmuch / emacs pipeline with tee, and found that what comes out of\r
+> ``notmuch | tee'' is still sane, so I'm fairly sure it's an Emacs /\r
+> notmuch elisp code issue.)\r
+>=20\r
+> And, 25 times the medium length of a ``notmuch search [...]'' output line\r
+> is... 4 KiB, the standard page size. Is this ``just'' a problem in the\r
+> notmuch elisp code, or is Emacs doing something awful with (wild\r
+> speculation...) short reads on buffer page boundaries (or whatever else)?\r
+\r
+I began to analyze this. Here is a dump of my steps.\r
+\r
+I used strace on the (already running) Emacs process. strace would log\r
+to several files: one for the main (Emacs) process, and a new one for\r
+each forked process. I can see that a ``notmuch search [...]'' process\r
+is fork()ed / exec()uted. It does a lot of read()ing from the DB, and\r
+write()s out the results record by record (which in our case means line\r
+by line). Up to the point where I examined, there have been no short\r
+writes. The log:\r
+\r
+ [some write()s for the first two dozen search results]\r
+ 16:26:54.143464 write(1, "thread:00000000000006c7 2009-12-16 [2/2] Th=\r
+omas Schwinge; [subject] ([flags])\n", 135) =3D 135\r
+ [...]\r
+ 16:26:54.266866 write(1, "thread:0000000000000ac4 2009-12-16 [1/1] js=\r
+m28@sourceware.org; [subject] ([flags])\n", 181) =3D 181\r
+\r
+At this / in the middle of this point, the 4 KiB size is hit. After\r
+accumulating some more (notice the 3.6 seconds delay), Emacs read()s the\r
+first chunk (line breaks inserted for clarity):\r
+\r
+ 16:26:57.928798 read(8, "[first two dozen results]"\r
+ "thread:00000000000006c7 2009-12-16 [2/2] Tho=\r
+mas Schwinge; [subject] ([flags])\n"\r
+ "t", 4096) =3D 4095\r
+\r
+The last result line is obviously incomplete, only the `t' so far.\r
+\r
+There is more to be read, so Emacs quickly goes on with the next chunk:\r
+\r
+ 16:26:57.966247 read(8, "hread:0000000000000ac4 2009-12-16 [1/1] jsm2=\r
+8@sourceware.org; [subject] ([flags])\n"\r
+ "[more results]", 4096) =3D 4095\r
+\r
+That's the remainder of the partial line, plus further results. This is\r
+all fine. It's now Emacs' job to re-assemble the two partial lines\r
+(thread ac4). I note that indeed this search result is missing in the\r
+notmuch-search buffer.\r
+\r
+(By the way, I wonder why read() returns 4095 bytes instead of 4096?)\r
+\r
+I'll next move on to debugging what actually appears at the elisp layer.\r
+I somehow don't think the Emacs core is faulty; probably rather our\r
+asynchronous results presentation layer handles partial lines\r
+incorrectly? More to come later.\r
+\r
+\r
+Gr=C3=BC=C3=9Fe,\r
+ Thomas\r
+\r
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+--=-=-=--\r
projects / notmuch-archives.git / commitdiff