kc3-lang/angle

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• Hash : 93b97a59
  Author :
  Date : 2023-11-03T22:07:23
  

  Make link job directly wait on compile job
  
  Previously, program link waited on the compile job on the calling thread
  before launching the link job.  As a result, sequences of intermixed
  compile and link would get largely serialized as such:
  
  Main Thread       Thread 1       Thread 2       Thread 3       Thread 4
   Compile -------> Compile
   Compile -----------|----------> Compile
   Link               |              |
     Wait             |              |
     |                |              |
     |<--------------/--------------/
     \------------------------------------------> Link
   Compile -------> Compile                        |
   Compile -----------|----------> Compile         |
   Link               |              |             |
     Wait             |              |             |
     |                |              |             |
     |<--------------/--------------/              |
     \---------------------------------------------|-----------> Link
   Compile -------> Compile                        |              |
   Compile -----------|----------> Compile         |              |
   Link               |              |             |              |
     Wait             |              |             |              |
     |                |              |             |              |
     ...
  
  With this change, the main thread no longer waits for compilation to
  finish.  It's the link job itself that does the waiting.  This allows
  the main thread to go through Compile and Link commands without
  blocking, generating as many jobs as needed.  The above scenario
  therefore becomes:
  
  Main     T1     T2     T3     T4     T5     T6     T7     T8     T9
   C ----> C
   C ------|----> C
   L ------|------|----> L
   C ------|------|-------W---> C
   C ------|------|-------|-----|----> C
   L ------|------|-------|-----|------|----> L
   C ------|------|-------|-----|------|-------W---> C
   C ------|------|-------|-----|------|-------|-----|----> C
   L ------|------|-------|-----|------|-------|-----|------|----> L
   .        \-----\------>/     |      |       |     |      |       W
   .                     |       \-----\------>/     |      |       |
   .                     |                    |       \-----\------>/
   .                     |                    |                    |
   .                     |                    |                    |
  
  This greatly improves the amount of parallelism compile and link jobs
  get.
  
  The careful observer may note that the link job being blocked on the
  compile job is now wasting a thread from the thread pool.  While this
  change is strictly an improvement, parallelism can be further improved
  if the link job is just not assigned to a thread until the corresponding
  compile jobs are finished.  This is currently not possible, but may be
  if:
  
  - Instead of a thread pool, the operating system's FIFO scheduler is
    used.  Then the operating system would automatically put blocking
    tasks to sleep and pick up another task.  This has the downside of
    requiring threads to be created for each task.
  - The thread pool work scheduler is enhanced to be made aware of
    relationship between tasks and avoid scheduling jobs whose
    dependencies are not yet met.
  
  Alternatively, the number of threads in the pool can be increased by 30%
  and hope for the best.
  
  Bug: angleproject:8297
  Change-Id: If4e6540ade47558a10cfab55e2286f073b904928
  Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5006874
  Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
  Reviewed-by: Geoff Lang <geofflang@chromium.org>
  Reviewed-by: Charlie Lao <cclao@google.com>
  

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