新增PDF生成并发设置

backend/app/services/pdf.py

@@ -1,5 +1,7 @@
+import threading
 from datetime import date, datetime, timedelta
 from pathlib import Path
+from time import monotonic
 
 from PIL import Image, ImageDraw, ImageFont
 
@@ -10,6 +12,35 @@ from app.models import Certificate, CertificateAccessToken, Learner, ProjectCour
 DESIGN_WIDTH = 1024
 DESIGN_HEIGHT = 759
 PDF_BASE_RESOLUTION = 150.0
+PDF_GENERATION_WAIT_TIMEOUT_SECONDS = 120
+
+
+class PdfGenerationBusy(RuntimeError):
+    pass
+
+
+class PdfGenerationLimiter:
+    def __init__(self) -> None:
+        self._condition = threading.Condition()
+        self._active = 0
+
+    def acquire(self, limit: int, timeout_seconds: int = PDF_GENERATION_WAIT_TIMEOUT_SECONDS) -> None:
+        deadline = monotonic() + timeout_seconds
+        with self._condition:
+            while self._active >= limit:
+                remaining = deadline - monotonic()
+                if remaining <= 0:
+                    raise PdfGenerationBusy("当前PDF生成任务较多，请稍后重试")
+                self._condition.wait(remaining)
+            self._active += 1
+
+    def release(self) -> None:
+        with self._condition:
+            self._active = max(0, self._active - 1)
+            self._condition.notify_all()
+
+
+pdf_generation_limiter = PdfGenerationLimiter()
 
 
 def pdf_cache_path(certificate_no: str) -> Path:
@@ -51,6 +82,7 @@ def render_certificate_pdf(
     learner: Learner,
     project: ProjectCourse | None,
     token: CertificateAccessToken,
+    concurrency_limit: int = 2,
 ) -> Path:
     output_path = pdf_cache_path(certificate.certificate_no)
     template_path = certificate_template_path()
@@ -60,8 +92,15 @@ def render_certificate_pdf(
         update_pdf_access_time(certificate)
         return output_path
 
-    image = render_certificate_image(certificate, learner, project)
-    image.save(output_path, "PDF", resolution=pdf_resolution(image))
+    pdf_generation_limiter.acquire(max(1, concurrency_limit))
+    try:
+        if cached_pdf_is_fresh(output_path) and output_path.stat().st_mtime >= latest_renderer_mtime:
+            update_pdf_access_time(certificate)
+            return output_path
+        image = render_certificate_image(certificate, learner, project)
+        image.save(output_path, "PDF", resolution=pdf_resolution(image))
+    finally:
+        pdf_generation_limiter.release()
 
     certificate.pdf_status = "generated"
     certificate.pdf_file_path = str(output_path)