SystemLayerImplSelect: libev: avoid timers firing early (#28434) #28740
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PR #28740: Size comparison from a40963d to 5182250 Increases (11 builds for bl602, bl702, psoc6, telink)
Decreases (12 builds for bl702l, efr32, esp32, k32w, nrfconnect, psoc6, telink)
Full report (60 builds for bl602, bl702, bl702l, cc32xx, cyw30739, efr32, esp32, k32w, linux, mbed, nrfconnect, psoc6, qpg, telink)
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PR #28740: Size comparison from cbc3865 to 2ccd2c3 Increases (11 builds for bl602, bl702, cyw30739, esp32, nrfconnect, telink)
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…roject-chip#28434) This fixes a ReportEngine problem that was caused by libev based timers firing slightly (in the range of 20mS) too early, because libev by default uses the time when events started processing as the "now" reference for relative timers for efficiency reasons. To ensure timers cannot fire early, timer setup must compensate for any difference between ev_now() which is the time events started processing and ev_time(), which is the actual current time (but is a bit less efficient to obtain). # Conflicts: # src/system/SystemLayerImplSelect.cpp
libev based regular builds do not need a separate I/O wakeup thread, so the wakeup thread can be eliminated in CHIP_SYSTEM_CONFIG_USE_LIBEV case. In normal operation, libev based builds also never call Signal(), so if it is still called it now emits a error log message, to indicate something might be wrong in the setup. However we keep Signal() and related LayerSocketsLoop methods, following the Darwin dispatch implementation, as fallback to select-based event handling seems to be needed for some I/O tests. As noted in a comment to the original libev PR [1], eventually, the select() based mainloop and external mainloop based solutions like Darwin Dispatch and libev should be detangled and extracted into separate classes, adapting all the tests that somehow rely on the select() fallback. As a single self-funded developer however, I cannot possibly be expected to solve this for Apple ;-) [1] project-chip#24232 (review)
- the fix prevents them in normal libev case - however the caller MUST NOT rely on timers *never* firing a bit early
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PR #28740: Size comparison from 96c6c7a to d201208 Decreases (1 build for efr32)
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…#28434) (project-chip#28740) * SystemLayerImplSelect: libev: avoid timers firing slightly too early (project-chip#28434) This fixes a ReportEngine problem that was caused by libev based timers firing slightly (in the range of 20mS) too early, because libev by default uses the time when events started processing as the "now" reference for relative timers for efficiency reasons. To ensure timers cannot fire early, timer setup must compensate for any difference between ev_now() which is the time events started processing and ev_time(), which is the actual current time (but is a bit less efficient to obtain). # Conflicts: # src/system/SystemLayerImplSelect.cpp * SystemLayerImplSelect: libev: eliminate I/O wakeup thread libev based regular builds do not need a separate I/O wakeup thread, so the wakeup thread can be eliminated in CHIP_SYSTEM_CONFIG_USE_LIBEV case. In normal operation, libev based builds also never call Signal(), so if it is still called it now emits a error log message, to indicate something might be wrong in the setup. However we keep Signal() and related LayerSocketsLoop methods, following the Darwin dispatch implementation, as fallback to select-based event handling seems to be needed for some I/O tests. As noted in a comment to the original libev PR [1], eventually, the select() based mainloop and external mainloop based solutions like Darwin Dispatch and libev should be detangled and extracted into separate classes, adapting all the tests that somehow rely on the select() fallback. As a single self-funded developer however, I cannot possibly be expected to solve this for Apple ;-) [1] project-chip#24232 (review) * SystemLayerImplSelect: reword comment: early firing timers can happen - the fix prevents them in normal libev case - however the caller MUST NOT rely on timers *never* firing a bit early
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Fixes #28434
This fixes a ReportEngine problem that was caused by libev-based timers firing slightly (in the range of 20mS) too early, because libev by default uses the time when events started processing as the "now" reference for relative timers for efficiency reasons.
To ensure timers cannot fire early, timer setup must compensate for any difference between ev_now() which is the time events started processing and ev_time(), which is the actual current time (but is a bit less efficient to obtain).
The PR also avoids and warns about useless (but harmless) calls to Signal() in libev case.