Improve performance of entropy build action (#1407)

* Use multiple threads for entropy builds

* Verify builds parameter

* Revert "Verify builds parameter"

This reverts commit 460d3d3b55.

* Use options instead

* Seed fix

* 256 samples on push

tools/multi-prepare.ps1

@@ -0,0 +1,81 @@
+if ($args.count -lt 2) {
+    Write-Error "Requires 2 args: job matrix number and number of builds for this job."
+    exit 1
+}
+
+function Get-BaseSeed {
+    Param (
+        [int]$Matrix
+    )
+
+    # GITHUB_SHA is the commit hash. This means the entropy files will be consistent
+    # unless you push a new commit.
+    $sha = [System.Convert]::ToUInt32($env:GITHUB_SHA.Substring(0, 8), 16)
+
+    # Mask off the last 16 bits
+    $base_seed = ($sha -band 0xffff0000)
+
+    # Add the matrix number * 256. We can run 256 unique builds on this job.
+    return $base_seed + ($Matrix -shl 8)
+}
+
+$MatrixNo = [int]$args[0]
+$BuildCount = [int]$args[1]
+$base_seed = $(Get-BaseSeed -Matrix $MatrixNo)
+
+$build_ids = 0..($BuildCount - 1)
+
+$build_dirs   = foreach($i in $build_ids) { "build$i" }
+$stdout_files = foreach($i in $build_ids) { "stdout$i.txt" }
+$stderr_files = foreach($i in $build_ids) { "stderr$i.txt" }
+
+$procs = New-Object System.Collections.Generic.List[System.Diagnostics.Process]
+
+foreach($i in $build_ids) {
+    # Create the entropy file
+    $entropy_file = "entropy$i.h"
+    $seed = $base_seed + $i
+
+    Write-Output "Using seed: $seed (instance $i)"
+    python3 tools/entropy.py $seed > $entropy_file
+
+    # Prepare to build
+    $params = @{
+        FilePath = "cmake"
+        PassThru = $null
+        ArgumentList = @(
+            "-B", $build_dirs[$i],
+            "-DCMAKE_BUILD_TYPE=RelWithDebInfo",
+            "-DISLE_INCLUDE_ENTROPY=ON",
+            "-DISLE_ENTROPY_FILENAME=$entropy_file",
+            "-G", "`"NMake Makefiles`""
+        )
+    }
+
+    # For the first job, display stdout and stderr.
+    # Else dump to file so we don't see 50 at once.
+    if ($i -eq 0) {
+        $params.Add("NoNewWindow", $null)
+    } else {
+        $params.Add("RedirectStandardOutput", $stdout_files[$i])
+        $params.Add("RedirectStandardError", $stderr_files[$i])
+    }
+
+    $procs.Add($(Start-Process @params))
+}
+
+$failed = $false
+try { Wait-Process -InputObject $procs } catch { $failed = $true }
+
+# Check for failure
+foreach($i in $build_ids) {
+    if ($procs[$i].ExitCode -ne 0) {
+        if ($i -ne 0) {
+            Get-Content $stdout_files[$i] -Tail 10
+            Get-Content $stderr_files[$i] -Tail 10
+        }
+        $failed = $true
+    }
+}
+
+if ($failed) { exit 1 }