0000863: Prevent race condition for read/write of savapage.json

Summary	0000863: Prevent race condition for read/write of savapage.json

Revision	2017-09-08 19:34 by rijkr
Description	IST: Sometimes, a "com.fasterxml.jackson.core.JsonParseException: Unexpected end-of-input in field name" is encountered when reading a user's savapage.json file. This indicates that the file is incomplete, which could be due to a read/write "race condition". For example, after a PDF upload, the UserEventService gets a notification from the Linux file system of the newly created PDF, and immediately reads the PDF meta data from the savapage.json file, while at the same time the same json file is being written by another thread. SOLL: Create savapage.json as temp file and do atomic move to target location. NOTE: This issue was observed on VMware with an extra mounted disk (XFS File System) dedicated for temporary files and user inboxes. On the same system it was also observed that an atomic file move sometimes fails, due to the fact that the source file is reported missing, although a Java File.exists(), just before the move, reports that the file is present.

Revision	2017-09-08 20:11 by rijkr
Description	IST: Sometimes, a "com.fasterxml.jackson.core.JsonParseException: Unexpected end-of-input in field name" is encountered when reading a user's savapage.json file. This indicates that the file is incomplete, which could be due to a read/write "race condition". For example, after a PDF upload, the UserEventService gets a notification from the Linux file system of the newly created PDF, and immediately reads the PDF meta data from the savapage.json file, while at the same time the same json file is being written by another thread. SOLL: Create savapage.json as temp file and do atomic move to target location. NOTE: This issue was observed on VMware with an extra mounted disk (XFS File System) dedicated for temporary files and user inboxes.

Revision	2017-09-08 20:34 by rijkr
Description	IST: Sometimes, a "com.fasterxml.jackson.core.JsonParseException: Unexpected end-of-input in field name" is encountered when reading a user's savapage.json file. This indicates that the file is incomplete, which could be due to a read/write "race condition". For example, after a PDF upload, the UserEventService gets a notification from the Linux file system of the newly created PDF, and immediately reads the PDF meta data from the savapage.json file, while at the same time the same json file is being written by another thread. SOLL: Create savapage.json as temp file and do atomic move to target location. NOTE: This issue was observed on VMware with an extra mounted disk (XFS File System) dedicated for temporary files and user inboxes.

Revision	2017-09-08 19:34 by rijkr
Additional Information	2017-09-07 14:56:23,468 ERROR UserEventService:559 - Error parsing from file [/opt/spool/savapage/safepages/0/1/some-userid/savapage.json] [jetty-threadpool-4604] org.savapage.core.SpException: Error parsing from file [/opt/spool/savapage/safepages/0/1/some-userid/savapage.json] at org.savapage.core.services.impl.InboxServiceImpl.readInboxInfo(InboxServiceImpl.java:191) at org.savapage.core.services.impl.InboxServiceImpl.getInboxInfo(InboxServiceImpl.java:244) at org.savapage.core.services.helpers.InboxPageImageChunker.<init>(InboxPageImageChunker.java:212) at org.savapage.core.services.helpers.InboxPageImageChunker.chunk(InboxPageImageChunker.java:663) at org.savapage.core.services.impl.InboxServiceImpl.getPageChunks(InboxServiceImpl.java:754) at org.savapage.server.cometd.UserEventService.getChangedJobsEvent(UserEventService.java:1031) at org.savapage.server.cometd.UserEventService.watchUserFileEvents(UserEventService.java:897) at org.savapage.server.cometd.UserEventService.monitorUserEvent(UserEventService.java:518) ... Caused by: com.fasterxml.jackson.core.JsonParseException: Unexpected end-of-input in field name at [Source: /opt/spool/savapage/safepages/0/1/some-userid/savapage.json; line: 168, column: 4010] at com.fasterxml.jackson.core.JsonParser._constructError(JsonParser.java:1378) .... at org.savapage.core.services.impl.InboxServiceImpl.readInboxInfo(InboxServiceImpl.java:171) ... 32 more 2017-09-07 14:56:23,473 ERROR AppLogServiceImpl:121 - UserEventService: SpException: Error parsing from file [/opt/spool/savapage/safepages/0/1/some-userid/savapage.json] (User "some-userid" at WebApp 127.0.0.1) [jetty-threadpool-4604]

Revision	2017-09-08 20:34 by rijkr
Additional Information	2017-09-07 14:56:23,468 ERROR UserEventService:559 - Error parsing from file [/opt/spool/savapage/safepages/0/1/some-userid/savapage.json] [jetty-threadpool-4604] org.savapage.core.SpException: Error parsing from file [/opt/spool/savapage/safepages/0/1/some-userid/savapage.json] at org.savapage.core.services.impl.InboxServiceImpl.readInboxInfo(InboxServiceImpl.java:191) at org.savapage.core.services.impl.InboxServiceImpl.getInboxInfo(InboxServiceImpl.java:244) at org.savapage.core.services.helpers.InboxPageImageChunker.<init>(InboxPageImageChunker.java:212) at org.savapage.core.services.helpers.InboxPageImageChunker.chunk(InboxPageImageChunker.java:663) at org.savapage.core.services.impl.InboxServiceImpl.getPageChunks(InboxServiceImpl.java:754) at org.savapage.server.cometd.UserEventService.getChangedJobsEvent(UserEventService.java:1031) at org.savapage.server.cometd.UserEventService.watchUserFileEvents(UserEventService.java:897) at org.savapage.server.cometd.UserEventService.monitorUserEvent(UserEventService.java:518) . . . Caused by: com.fasterxml.jackson.core.JsonParseException: Unexpected end-of-input in field name at [Source: /opt/spool/savapage/safepages/0/1/some-userid/savapage.json; line: 168, column: 4010] at com.fasterxml.jackson.core.JsonParser._constructError(JsonParser.java:1378) . . . at org.savapage.core.services.impl.InboxServiceImpl.readInboxInfo(InboxServiceImpl.java:171) ... 32 more 2017-09-07 14:56:23,473 ERROR AppLogServiceImpl:121 - UserEventService: SpException: Error parsing from file [/opt/spool/savapage/safepages/0/1/some-userid/savapage.json] (User "some-userid" at WebApp 127.0.0.1) [jetty-threadpool-4604]

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