Add support for changing subprocess priority.

Author: yangerhang

include/vcpkg/base/contractual-constants.h

@@ -546,6 +546,7 @@ namespace vcpkg
     inline constexpr StringLiteral EnvironmentVariableVcpkgForceSystemBinaries = "VCPKG_FORCE_SYSTEM_BINARIES";
     inline constexpr StringLiteral EnvironmentVariableVcpkgKeepEnvVars = "VCPKG_KEEP_ENV_VARS";
     inline constexpr StringLiteral EnvironmentVariableVcpkgMaxConcurrency = "VCPKG_MAX_CONCURRENCY";
+    inline constexpr StringLiteral EnvironmentVariableVcpkgSubprocessPriority = "VCPKG_SUBPROCESS_PRIORITY";
     inline constexpr StringLiteral EnvironmentVariableVcpkgNoCi = "VCPKG_NO_CI";
     inline constexpr StringLiteral EnvironmentVariableVcpkgNuGetRepository = "VCPKG_NUGET_REPOSITORY";
     inline constexpr StringLiteral EnvironmentVariableVcpkgOverlayPorts = "VCPKG_OVERLAY_PORTS";

include/vcpkg/base/message-data.inc.h

@@ -1147,6 +1147,11 @@ DECLARE_MESSAGE(EnvInvalidMaxConcurrency,
                 (msg::env_var, msg::value),
                 "{value} is the invalid value of an environment variable",
                 "{env_var} is {value}, must be > 0")
+DECLARE_MESSAGE(EnvInvalidPriority,
+                (msg::env_var, msg::value),
+                "'{value} is a user-supplied value for {env_var} environment variable.'",
+                "invalid value \"{value}\" for {env_var}."
+                "Valid values are '', 'IDLE', 'BELOW_NORMAL', 'NORMAL', 'ABOVE_NORMAL', 'HIGH' and 'REALTIME'")
 DECLARE_MESSAGE(EnvStrFailedToExtract, (), "", "could not expand the environment string:")
 DECLARE_MESSAGE(EnvPlatformNotSupported, (), "", "Build environment commands are not supported on this platform")
 DECLARE_MESSAGE(EnvVarMustBeAbsolutePath, (msg::path, msg::env_var), "", "{env_var} ({path}) was not an absolute path")

include/vcpkg/base/system.h

@@ -62,6 +62,10 @@ namespace vcpkg
     const Optional<Path>& get_program_files_platform_bitness();
 
     unsigned int get_concurrency();
+    
+#if defined(_WIN32)
+    DWORD get_subprocess_priority();
+#endif
 
     Optional<CPUArchitecture> guess_visual_studio_prompt_target_architecture();
 }

src/vcpkg/base/system.cpp

@@ -733,6 +733,53 @@ namespace vcpkg
         return concurrency;
     }
 
+#if defined(_WIN32)
+    DWORD get_subprocess_priority()
+    {
+        static const DWORD priority = []() {
+            const auto opt_user_defined_priority = get_environment_variable(EnvironmentVariableVcpkgSubprocessPriority);
+            if (!opt_user_defined_priority.has_value())
+            {
+                return IDLE_PRIORITY_CLASS;
+            }
+            const auto user_defined_priority = opt_user_defined_priority.value_or_exit(VCPKG_LINE_INFO);
+            if (user_defined_priority.empty() || Strings::case_insensitive_ascii_equals(user_defined_priority, "idle"))
+            {
+                return IDLE_PRIORITY_CLASS;
+            }
+            else if (Strings::case_insensitive_ascii_equals(user_defined_priority, "below_normal"))
+            {
+                return BELOW_NORMAL_PRIORITY_CLASS;
+            }
+            else if (Strings::case_insensitive_ascii_equals(user_defined_priority, "normal"))
+            {
+                return NORMAL_PRIORITY_CLASS;
+            }
+            else if (Strings::case_insensitive_ascii_equals(user_defined_priority, "above_normal"))
+            {
+                return ABOVE_NORMAL_PRIORITY_CLASS;
+            }
+            else if (Strings::case_insensitive_ascii_equals(user_defined_priority, "high"))
+            {
+                return HIGH_PRIORITY_CLASS;
+            }
+            else if (Strings::case_insensitive_ascii_equals(user_defined_priority, "realtime"))
+            {
+                return REALTIME_PRIORITY_CLASS;
+            }
+            else
+            {
+                Checks::msg_exit_with_message(VCPKG_LINE_INFO,
+                                              msgEnvInvalidPriority,
+                                              msg::env_var = EnvironmentVariableVcpkgSubprocessPriority,
+                                              msg::value = user_defined_priority);
+            }
+            return IDLE_PRIORITY_CLASS;
+        }();
+        return priority;
+    }
+#endif
+
     Optional<CPUArchitecture> guess_visual_studio_prompt_target_architecture()
     {
         // Check for the "vsdevcmd" infrastructure used by Visual Studio 2017 and later

src/vcpkg/base/system.process.cpp

@@ -818,6 +818,8 @@ namespace
             call_environment = environment_block.data();
         }
 
+        DWORD dwPriority = get_subprocess_priority();
+
         // Leaking process information handle 'process_info.proc_info.hProcess'
         // /analyze can't tell that we transferred ownership here
         VCPKG_MSVC_WARNING(suppress : 6335)
@@ -826,7 +828,7 @@ namespace
                             nullptr,
                             nullptr,
                             bInheritHandles,
-                            IDLE_PRIORITY_CLASS | CREATE_UNICODE_ENVIRONMENT | EXTENDED_STARTUPINFO_PRESENT |
+                            dwPriority | CREATE_UNICODE_ENVIRONMENT | EXTENDED_STARTUPINFO_PRESENT |
                                 dwCreationFlags,
                             call_environment,
                             working_directory_arg,